TCP/IPOSI Open Systems InterconnectionISO International Organization for Standardization Each TCP/IP application typically chooses to use either TCP or UDP based on the applications requirements. For example TCP provides error recovery, but to do so, it consumes more bandwidth and uses more processing cycles. UDP does not do error recovery, but it takes less bandwidth and uses fewer process cycles. TCP provides a variety of useful features, including error recovery, in fact, TCP is best known for its error-recovery feature. TCP/IP defines a large collection of protocols that allow computer to communicate.

TCP/IP defines the details of each of these protocols inside documents calledRFC Requests For CommentsThe TCP/IP transport layer consist of two main protocol options The Transmission control Protocol (TCP)andThe User Datagram Protocol (UDP).Same-Layer interaction on different computers:The two computers use a protocol to communicate with the same layer on another computer. The Protocol defined by each layer uses a header that is transmitted between the computers. To communicate what each computer want to do.Adjacent-layer interaction on the same computer: On a single computer, one layer provides a service to a higher layer. The software or hardware that implements the higher layer requests that the next lower layer perform the needed function.

. TCP/IP Network Interface Layer (Data Link layer)The network interface layer defines the protocols and hardware required to deliver data across some physical network. The term network interface refers to the fact that this layer defines how to connect the host computer, which is not part of the network, to the network; it is the interface between the computer and the network. The Internet protocol suite includes not only lower-level specifications (such as TCP and IP), but specifications for such common applications as electronic mail, terminal emulation, and file transfer. Figure 1 shows some of the more important Internet protocols and their relationship to the OSI Reference Model.The Internet protocols are the most widely implemented multivendor protocol suite in use today. Support for at least part of the Internet protocol suite is available from virtually every computer vendor.TCP/IP TechnologyThis section describes technical aspects of TCP, IP, related protocols, and the environments in which these protocols operate. Because the primary focus of this document is routing (a layer 3 function), the discussion of TCP (a layer 4 protocol) will be relatively brief.TCPTCP is a connection-oriented transport protocol that sends data as an unstructured stream of bytes. By using sequence numbers and acknowledgment messages, TCP can provide a sending node with delivery information about packets transmitted to a destination node. Where data has been lost in transit from source to destination, TCP can retransmit the data until either a timeout condition is reached or until successful delivery has been achieved. TCP can also recognize duplicate messages and will discard them appropriately. If the sending computer is transmitting too fast for the receiving computer, TCP can employ flow control mechanisms to slow data transfer. TCP can also communicate delivery information to the upper-layer protocols and applications it supports.IPIP is the primary layer 3 protocol in the Internet suite. In addition to internetwork routing, IP provides error reporting and fragmentation and reassembly of information units called datagrams for transmission over networks with different maximum data unit sizes. IP represents the heart of the Internet protocol suite.IP addresses are globally unique, 32-bit numbers assigned by the Network Information Center. Globally unique addresses permit IP networks anywhere in the world to communicate with each other.An IP address is divided into three parts. The first part designates the network address, the second part designates the subnet address, and the third part designates the host address. IP addressing supports three different network classes. Class A networks are intended mainly for use with a few very large networks, because they provide only 8 bits for the network address field. Class B networks allocate 16 bits, and Class C networks allocate 24 bits for the network address field. Class C networks only provide 8 bits for the host field, however, so the number of hosts per network may be a limiting factor. In all three cases, the leftmost bit(s) indicate the network class. IP addresses are written in dotted decimal format; for example, 34.0.0.1. Figure 2 shows the address formats for Class A, B, and C IP networks.IP networks also can be divided into smaller units called subnetworks or "subnets." Subnets provide extra flexibility for the network administrator. For example, assume that a network has been assigned a Class A address and all the nodes on the network use a Class A address. Further assume that the dotted decimal representation of this network's address is 34.0.0.0. (All zeros in the host field of an address specify the entire network.) The administrator can subdivide the network using subnetting. This is done by "borrowing" bits from the host portion of the address and using them as a subnet field.If the network administrator has chosen to use 8 bits of subnetting, the second octet of a Class A IP address provides the subnet number. In our example, address 34.1.0.0 refers to network 34, subnet 1; address 34.2.0.0 refers to network 34, subnet 2, and so on.The number of bits that can be borrowed for the subnet address varies. To specify how many bits are used and where they are located in the host field, IP provides subnet masks. Subnet masks use the same format and representation technique as IP addresses. Subnet masks have ones in all bits except those that specify the host field. For example, the subnet mask that specifies 8 bits of subnetting for Class A address 34.0.0.0 is 255.255.0.0. The subnet mask that specifies 16 bits of subnetting for Class A address 34.0.0.0 is 255.255.255.0. Both of these subnet masks are pictured in Figure 4. Subnet masks can be passed through a network on demand so that new nodes can learn how many bits of subnetting are being used on their network.As IP subnets have grown, administrators have looked for ways to use their address space more efficiently. One of the techniques that has resulted is called Variable Length Subnet Masks (VLSM). With VLSM, a network administrator can use a long mask on networks with few hosts and a short mask on subnets with many hosts. However, this technique is more complex than making them all one size, and addresses must be assigned carefully.Of course in order to use VLSM, a network administrator must use a routing protocol that supports it. Cisco routers support VLSM with Open Shortest Path First (OSPF), Integrated Intermediate System to Intermediate System (Integrated IS-IS), Enhanced Interior Gateway Routing Protocol (Enhanced IGRP), and static routing.On some media, such as IEEE 802 LANs, IP addresses are dynamically discovered through the use of two other members of the Internet protocol suite: Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP). ARP uses broadcast messages to determine the hardware (MAC layer) address corresponding to a particular network-layer address. ARP is sufficiently generic to allow use of IP with virtually any type of underlying media access mechanism. RARP uses broadcast messages to determine the network-layer address associated with a particular hardware address. RARP is especially important to diskless nodes, for which network-layer addresses usually are unknown at boot time.

TCP/IP Architectural Model and ExamplesTCP/IP Architecture LayerExample ProtocolsApplicationHTTP, SMTP,TFTP, SMTP, FTP, TELNET TransportTCP, UDP InternetIPNetwork AccessEthernet, FDDI, ATM, Frame Relay

TCP/IP Architectural Model OSI Model

Application LayersProtocolsApplication (7) Application

(6) Prentation

Data Flow LayersTransport (4) Transport (5) Session

NetworksInternet (3) Network

Network Access (2) Data Link

Physical

TCP/IP protocolApplication ---------------------------------- (HTTP)Transport ------------------------------------ (UDP, TCP)Internet---------------------------------------- (IP) **********OnlyNetwork Access -------------------- (Ethernet, PPP, HDLC, Frame Relay)

PC sends out Frames which holds Packets which holds Segments which hold IP Packets headers which holds the source and destination address and data from the application data hold IP address and Data from the Application layer. TCP/IP Encapsulation Frame(L2)L Packet (only adds header (L3)) Segment(L4)

Internet IPTCP & DataApplicationTransportInternetEthernet (LH) Ethernet (LT)

LANS WAN WANLayers-------------------

Routers Routers PC and Switches

Network Access uses WAN and LAN protocols used to move Packets from the source to the destination. Based on where the frame is in the network decides what Network Access protocol to use WAN or LAN protocolsLAN Protocols = Ethernet Protocol (Mac addresses)Wan Protocols = PPP, HDLC, Frame Relay (holds the type of packet)LANS protocols work with = PC Switch PCWANS protocols work with = Router Router IP is the only Transport protocol layer in TCP/IP.TCP/IP Encapsulation1) Application = Data2) TCP + Data = Transport3) IP + TCP + Data = Internet = Packet4) LH + IP + TCP + Data + LT = Network Access = Frame5) Transmit Frame*****LH = Link Header*****LT = Link TrailerEthernet Headers and Trailer hold the source MAC address and Destination MAC address. Maximum Bytes is 1500bytes MTU in 802.3 standard Ethernet.

802.3 -------------------Standard Ethernet10mbps10base T100m(Copper)802.3u ----------------------- Fast Ethernet 100mbps1000basetx100m(Copper)802.3z --------------------Gigabit Ethernet1000mbps1000baseLX5kilo(Fiber)1000baseSX550m(Fiber)802.3ab--------------------Gigabit Ethernet 1000mbps1000bseeT100m(Copper)

T= Twisted PairTX= Fast Ethernet

Typical Features of OSI Layer 3A Protocol that defines routing and addressing is considered to be a Network Layer 3, Protocol. OSI does define a unique Layer 3 protocol called Connectionless Network Services (CLNS). Layer 3 Protocols which deals with ROUTING and ADDRESSING:Internet Protocol (IP) Novell Internetwork Packet Exchange (IPX)AppleTalk Datagram Delivery Protocol (DDP)*****Ethernet LANs use MAC*****TCP/IP use IP address to get from one pc to another (Route).NETWORK LAYER (LAYER 3) ADDRESSINGIn TCP/IP this group is called a NETWORK or SUBNET. In IPX, it is called a NetworkIn Apple talk the grouping is called a CABLE RANGEThese groupings work just like U.S.P.S ZIP codes, allowing the routers (Mail Sorters) to speedily route (sort) lots of packets (letters).The routing table from each network layer protocol can have one entry for the group, not one entry for each individual IP address. A router needing to forward packets to any of those hosts needs one entry in its IP routing table. This basic fact is one of the key reason that router can scale to allow tens and hundreds of thousands of devices. A ROUTING PROTOCOL learns routes and puts those routes in a routing table.A ROUTED PROTOCOL is the type of packet forwarded or routed, thought a network.IP would be the ROUTED PROTOCOL Routing Information Protocol (RIP) which is used to learn routes would be considered the ROUTING PROTOCOL.Typical Features of OSI Layer 4The Transport layer (LAYER 4) defines several functions, the most important of which are Error Recovery and Flow Control. Router discard packets for many reasons including: BIT Errors

Network Congestion

INSTANCES WHICH THERE ARE NO ROUTES KNOWN

OSI Transport Layer Features: Connection-Oriented or Connections-Less

Error Recovery

Reliability

Flow Control

Segmenting

TCP provides a variety of useful features including error recovery. In fact, TCP is best known for its error-recovery feature but it does more. TCP performs the following functions: Multiplexing using port number

Error Recovery (reliability)

Flow control using windowing

Connection establishment and termination

End-to end ordered data transfer

Segmentation

TCP relies on IP for end-to-end delivery of the data, including routing issues.

TCP and UDP both use a concept called multiplexing.

UDP data transfer differs form TCP data transfer in that no reordering or recovery is accomplished.

The Transmission control Protocol (TCP) and the User Datagram Protocol (UDP) are two specific transport layer protocols they are Layer 4 protocols.

Typical Features of OSI Layer 4The transport layer (Layer 4) Defines several function, the most important of which are: Connection-Oriented or Connectionless Defines whether the protocol establishes some correlation between to end ports before any user data is allowed to be transferred (connection oriented) or not(Connectionless)

Error recovery The process of noticing errors or lost segments and causing them to be resent.

Reliability Another term for error recovery.

Flow Control- Process that control the rate at which data is transferred between two endpoints.

Segmenting application data Application layer protocols may need to send large chunks of data much larger than can fit inside one IP packet. The transport layer is responsible for segmenting the larger data into pieces, called SEGMENTS that can fit inside a packet.

Multiplexing using TCP port NumbersTCP and UDP both use a concept called multiplexing.Multiplexing by TCP and UDP involves the process of how a computer thins when receiving data. The computer might be running may application, such as a web browser, and e-mal package, or an FTP client. TCP and UDP multiplexing enables the receiving computer to know which application to give the data to.TCP and UDP solve this problem by using a port number field in the TCP or UDP header, respectively. Multiplexing relies on the use of a concept called a SOCKET. A socket consists of three things: IP address (xxxx.xxxx.xxxx.xxxx)

A Transport Protocol (UDP, TCP)

A Port number (23, 21, 53, 110)

The fact that each connection between tow sockets is unique means that you can use multiple application at the same time talking to application running on the same or different computer; multiplexing, based on sockets, ensures that the data is delivered to the correct applications. Transport Protocols UDP and TCP uses Port numbers also. 1030 is a port number used by the TCP/UDP connection. Port Numbers stat at 1024 because ports below 1024 are reserved for well know applications, such as web servers port 80.PC clients are required to include both the Source and the Destination Port numbers the port number used by the servers must be the well know.Source Port Numbers (Sockets)Destination Port numbers (Sockets)PC client ports Web Server ports102480103080104080 TCP header and the Data (Application) field together are called a TCP segment or L4PDU Layer 4 Protocol Data Unit.

Popular application and their well known Prot numbersPort NumberProtocolApplication

20TCPFTP data21TCPFTP control23TCPTelnet25TCPSMTP53UDP/TCPDNS67, 68UDP/TCPDHCP69UPPTFTP80TCPHTTP (WWW)110TCPPOP3161UDPSNMPError Recovery (Reliably)TCP provides for reliable data transfer, which is also called RELIABILITY or ERROR Recovery, depending of what document you read. To accomplish reliability, TCP numbers data bytes using the Sequence and Acknowledgment fields in the TCP header, TCP achieves reliability in both directions, using the Sequence Number field and one direction combined with the Acknowledgment field in the opposite direction.Flow control using WindowingTCP implement flow control by taking advantage of the sequence and Acknowledgment fields in the TCP header, along with another field called the Window field. This window field implies the maximum number of unacknowledged bytes allowed outstanding at any instant in time. The window starts small and then grows until errors occur. The window then slides up and down based on network performance. So it is sometimes called a Sliding Window. When the window is full, the sender will not send, which controls the flow of data.

Connection Establishment and TerminationTCP connection establishment occurs before any of the other TCP features can begin their work. Connection establishment refers to the process of initializing sequence and acknowledgment fields and agreeing to port numbers used. TCP connection- Establishment is a THREE WAY CONNECTION ESTABLISHMEN flow must be completed before data can begin. The connection exists between the two sockets, although there is no single socket field in TCP header. Of the three pats of a socket, IP address are implied based on the source and destination IP address in the IP header. TCP is implied because TCP header is in use,

TCP connection termination. This is a four- way termination sequence is straightforward and uses an additional flag, called the FIN bit. (FIN is short for FINISHED

Connectionless and Connection-Oriented ProtocolsThe terms connection-oriented and connectionless have some relatively well-known connotations inside the world of networking protocols. The meaning of the term is intertwined with error recovery and flow control, but they are not the same. Connections-Oriented protocol A protocol either that requires an exchange of misusages before data transfer begins or that has a required pre-established correlation between two end points.

Connectionless protocol A protocol that does not require an exchange of messages and that does not require a pre-established correlation between two endpoints.

TCP is indeed connection oriented because of the set of three messages that establish a TCP connection. Likewise Sequenced Packet Exchange (SPX), a transport layer protocol form Novell, is connection oriented. When using permanent virtual circuits (PVC), Frame relay does not require any messages to be send ahead of time, but it does require predefinition in the Frame Relay switches. Establishing a connection between Two Frame Relay attached devices. Many people confuse the real meaning of connection-Oriented with the definition of a reliable or error-recovering, protocol. TCP happens to do both, but just because a protocol is connection-oriented does not mean that is also performs error recovery.

Protocol Characteristics: Recover and Connections:Connected?Reliable?Examples

Connection-OrientedYESLLC TYPE 2(802.2), TCP, NOVELL SPX

Connection-OrientedNOFrame Relay VC, ATM VCs, PPP

ConnectionlessYESFTTP, NetWare NCP (No Packet Burst)

ConnectionlessNoUDP, IP, Most Layer 3 ProtocolsData Segmentation and Ordered Data TransferEach different type of data link protocol typically has a limit on the Maximum Transmission Unit (MTU) that can be sent. MTU refers to the size of the data according to the data link-Layer in other words, the size of the Layer 3 Packet that sits inside the data field of a frame. For many data link protocols, Ethernet included, the MTU is 1500 bytesTCP handles the fact that an application might give it millions of bytes to send by Segmenting the data into smaller pieces, called segments. Because an IP packet can often be no more the 1500 bytes, and because IP and TCP header are 20 bytes each, TCP typically segments large data into 1460 bytes (or smaller)segments. You should also be aware of some terminology related to TCP segmentation. The TCP header, along with the data field, together is called a TCP SEGMENT.

The term L4PDU can also be used instead of the term TCP segment because TCP is a Layer 4 Protocol

TCP FUNCTION SummaryFunctionMultiplexing Function that allows receiving host to decide the correct application, for which the data is destined, based on the port number.Error recover (reliability) Process of numbering and acknowledging data with Sequence and Acknowledgment header fields.Flow control using Windowing Process that uses window sizes to protect buffer space and routing devices.Connection Establishment and Termination Process used to initialize port numbers and sequence Acknowledgments fields.Ordered data transfer and data segmentation Continuous steam of Bytes for upper-layer process that is segmented for transmission and delivery to upper-Layer process at the receiving device, with the bytes in the same orderThe User Datagram ProtocolUDP provides a service for application to exchange messages. Unlike TCP, UDP is connectionless and Provides NO: NO Reliability NO Windowing NO Re-Ordering of the received data

However UDP provides some function of TCP:Does Provide Does Do Data Transfers Does Do Segmentation Does Do Multiplexing using port numbers.

And it does it with fewer bytes of overhead and with less processing required.

IP ADDRESSING DEFINITIONSIf a device wants to communicate using TCP/IP, it needs an IP address.When the device has an IP address and the appropriate software and hardware, it can send and receive IP packets. Any device that can send and receive IP packets is called an IP host.IP address consists of a 32-bit number, usually written in dotted-decimal notation. The decimal part of the term comes form the fact that each byte (8 bits) of the 32-bit address is converted to its decimal equivalent. The four resulting decimal numbers are written in sequence, with dots, or decimal points, separating the numbers hence the name dotted-decimal. Each of the decimal number in an IP address is called an octet. The term octet is just a vendor-neutral term instead of byte. So, for an IP address of 168.1.1.1, the first octet is 168, the second octet is 1, and son on. The range of decimal numbers in each octet is between 0 and 255, inclusive.

Data Encapsulation The term encapsulation describes the process of putting headers and trailer around some data.

The complete process of data encapsulation with TCP/IP is a FIVE STEP process.

This included the typical encapsulation by the application, Transport, network, and network interface (referred to as data link) layers as steps 1 through 4 in the five step processes. The fifth step was the physical layers transmission of the bit stream. STEP 1Create the application data and headers This simply means that the application has the data to send.STEP 2Package the data for transport In other words, the transport layer (TCP or UDP) creates the transport header and places the data behind it.STEP 3Add the destination and source network layer addresses to the data- The network layer creates the network header, which includes the network layer address, and places the data behind it. STEP 4Add the destination and source data link layer addresses to the data The data link layer creates the data link header, places the data behind it, and places the data link trailer at the end.STEP 5Transmit the bits- The physical layer encodes a signal onto the medium to transmit the frame.

Internet Protocols

Background

Internet Protocol (IP) The Internet Protocol (IP) is a network-layer (Layer 3) protocol that contains addressing information and some control information that enables packets to be routed. IP is documented in RFC 791 and is the primary network-layer protocol in the Internet protocol suite. Along with the Transmission Control Protocol (TCP), IP represents the heart of the Internet protocols. IP has two primary responsibilities: providing connectionless, best-effort delivery of datagrams through an internetwork; and providing fragmentation and reassembly of datagrams to support data links with different maximum-transmission unit (MTU) sizes.

IP Addressing As with any other network-layer protocol, the IP addressing scheme is integral to the process of routing IP datagrams through an internetwork. Each IP address has specific components and follows a basic format. These IP addresses can be subdivided and used to create addresses for subnetworks, as discussed in more detail later in this chapter. Each host on a TCP/IP network is assigned a unique 32-bit logical address that is divided into two main parts: the network number and the host number. The network number identifies a network and must be assigned by the Internet Network Information Center (InterNIC) if the network is to be part of the Internet. An Internet Service Provider (ISP) can obtain blocks of network addresses from the InterNIC and can itself assign address space as necessary. The host number identifies a host on a network and is assigned by the local network administrator. IP Address Format The 32-bit IP address is grouped eight bits at a time, separated by dots, and represented in decimal format (known as dotted decimal notation). Each bit in the octet has a binary weight (128, 64, 32, 16, 8, 4, 2, 1). The minimum value for an octet is 0, and the maximum value for an octet is 255. illustrates the basic format of an IP address. Figure30-3 An IP address consists of 32 bits, grouped into four octets.

I

IP Address Classes IP addressing supports five different address classes: A, B,C, D, and E. Only classes A, B, and C are available for commercial use. The left-most (high-order) bits indicate the network class. provides reference information about the five IP address classes. Table30-1 Reference Information About the Five IP Address Classes IP Address Class Format Purpose High-Order Bit(s) Address Range No. Bits Network/Host Max. Hosts

A N.H.H.H1 Few large organizations 0 1.0.0.0 to 126.0.0.0 7/24 167772142 (224 - 2)

B N.N.H.H Medium-size organizations 1, 0 128.1.0.0 to 191.254.0.0 14/16 65534 (216 - 2)

C N.N.N.H Relatively small organizations 1, 1, 0 192.0.1.0 to 223.255.254.0 21/8 254 (28 - 2)

D N/A Multicast groups (RFC 1112) 1, 1, 1, 0 224.0.0.0 to 239.255.255.255 N/A (not for commercial use) N/A

E N/A Experimental 1, 1, 1, 1 240.0.0.0 to 254.255.255.255 N/A N/A

1 N = Network number, H = Host number. 2 One address is reserved for the broadcast address, and one address is reserved for the network.

illustrates the format of the commercial IP address classes. (Note the high-order bits in each class.) Figure30-4 IP address formats A, B, and C are available for commercial use.

The class of address can be determined easily by examining the first octet of the address and mapping that value to a class range in the following table. In an IP address of 172.31.1.2, for example, the first octet is 172. Because 172 falls between 128 and 191, 172.31.1.2 is a Class B address. summarizes the range of possible values for the first octet of each address class. Figure30-5 A range of possible values exists for the first octet of each address class.

IP Subnet Addressing IP networks can be divided into smaller networks called subnetworks (or subnets). Subnetting provides the network administrator with several benefits, including extra flexibility, more efficient use of network addresses, and the capability to contain broadcast traffic (a broadcast will not cross a router). Subnets are under local administration. As such, the outside world sees an organization as a single network and has no detailed knowledge of the organization's internal structure. A given network address can be broken up into many subnetworks. For example, 172.16.1.0, 172.16.2.0, 172.16.3.0, and 172.16.4.0 are all subnets within network 171.16.0.0. (All 0s in the host portion of an address specifies the entire network.)

IP Subnet Mask A subnet address is created by "borrowing" bits from the host field and designating them as the subnet field. The number of borrowed bits varies and is specified by the subnet mask. shows how bits are borrowed from the host address field to create the subnet address field. Figure30-6 Bits are borrowed from the host address field to create the subnet address field.

Subnet masks use the same format and representation technique as IP addresses. The subnet mask, however, has binary 1s in all bits specifying the network and subnetwork fields, and binary 0s in all bits specifying the host field. illustrates a sample subnet mask. Figure30-7 A sample subnet mask consists of all binary 1s and 0s.

Subnet mask bits should come from the high-order (left-most) bits of the host field, as illustrates. Details of Class B and C subnet mask types follow. Class A addresses are not discussed in this chapter because they generally are subnetted on an 8-bit boundary.

Figure30-8 Subnet mask bits come from the high-order bits of the host field.

Various types of subnet masks exist for Class B and C subnets. The default subnet mask for a Class B address that has no subnetting is 255.255.0.0, while the subnet mask for a Class B address 171.16.0.0 that specifies eight bits of subnetting is 255.255.255.0. The reason for this is that eight bits of subnetting or 28 - 2 (1 for the network address and 1 for the broadcast address) = 254 subnets possible, with 28 - 2 = 254 hosts per subnet. The subnet mask for a Class C address 192.168.2.0 that specifies five bits of subnetting is 255.255.255.248.With five bits available for subnetting, 25 - 2 = 30 subnets possible, with 23 - 2 = 6 hosts per subnet. The reference charts shown in table 30-2 and table 30-3 can be used when planning Class B and C networks to determine the required number of subnets and hosts, and the appropriate subnet mask.

Table30-2 Class B Subnetting Reference Chart Number of Bits Subnet Mask Number of Subnets Number of Hosts

2 255.255.192.0 2 16382

3 255.255.224.0 6 8190

4 255.255.240.0 14 4094

5 255.255.248.0 30 2046

6 255.255.252.0 62 1022

7 255.255.254.0 126 510

8 255.255.255.0 254 254

9 255.255.255.128 510 126

10 255.255.255.192 1022 62

11 255.255.255.224 2046 30

12 255.255.255.240 4094 14

13 255.255.255.248 8190 6

14 255.255.255.252 16382 2

Table30-3 Class C Subnetting Reference Chart Number of Bits Subnet Mask Number of Subnets Number of Hosts

2 255.255.255.192 2 62

3 255.255.255.224 6 30

4 255.255.255.240 14 14

5 255.255.255.248 30 6

6 255.255.255.252 62 2

How Subnet Masks are Used to Determine the Network Number The router performs a set process to determine the network (or more specifically, the subnetwork) address. First, the router extracts the IP destination address from the incoming packet and retrieves the internal subnet mask. It then performs a logical AND operation to obtain the network number. This causes the host portion of the IP destination address to be removed, while the destination network number remains. The router then looks up the destination network number and matches it with an outgoing interface. Finally, it forwards the frame to the destination IP address. Specifics regarding the logical AND operation are discussed in the following section.

Logical AND Operation Three basic rules govern logically "ANDing" two binary numbers. First, 1 "ANDed" with 1 yields 1. Second, 1 "ANDed" with 0 yields 0. Finally, 0 "ANDed" with 0 yields 0. The truth table provided in table 30-4 illustrates the rules for logical AND operations. Table30-4 Rules for Logical AND Operations Input Input Output

1 1 1

1 0 0

0 1 0

0 0 0

Two simple guidelines exist for remembering logical AND operations: Logically "ANDing" a 1 with a 1 yields the original value, and logically "ANDing" a 0 with any number yields 0. illustrates that when a logical AND of the destination IP address and the subnet mask is performed, the subnetwork number remains, which the router uses to forward the packet. Figure30-9 Applying a logical AND the destination IP address and the subnet mask produces the subnetwork number.

Address Resolution Protocol (ARP) Overview For two machines on a given network to communicate, they must know the other machine's physical (or MAC) addresses. By broadcasting Address Resolution Protocols (ARPs), a host can dynamically discover the MAC-layer address corresponding to a particular IP network-layer address. After receiving a MAC-layer address, IP devices create an ARP cache to store the recently acquired IP-to-MAC address mapping, thus avoiding having to broadcast ARPS when they want to recontact a device. If the device does not respond within a specified time frame, the cache entry is flushed. In addition to the Reverse Address Resolution Protocol (RARP) is used to map MAC-layer addresses to IP addresses. RARP, which is the logical inverse of ARP, might be used by diskless workstations that do not know their IP addresses when they boot. RARP relies on the presence of a RARP server with table entries of MAC-layer-to-IP address mappings. Internet Routing Internet routing devices traditionally have been called gateways. In today's terminology, however, the term gateway refers specifically to a device that performs application-layer protocol translation between devices. Interior gateways refer to devices that perform these protocol functions between machines or networks under the same administrative control or authority, such as a corporation's internal network. These are known as autonomous systems. Exterior gateways perform protocol functions between independent networks. Routers within the Internet are organized hierarchically. Routers used for information exchange within autonomous systems are called interior routers, which use a variety of Interior Gateway Protocols (IGPs) to accomplish this purpose. The Routing Information Protocol (RIP) is an example of an IGP. Routers that move information between autonomous systems are called exterior routers. These routers use an exterior gateway protocol to exchange information between autonomous systems. The Border Gateway Protocol (BGP) is an example of an exterior gateway protocol.

NoteSpecific routing protocols, including BGP and RIP, are addressed in individual chapters presented in Part 6 later in this book.

IP Routing IP routing protocols are dynamic. Dynamic routing calls for routes to be calculated automatically at regular intervals by software in routing devices. This contrasts with static routing, where routers are established by the network administrator and do not change until the network administrator changes them. An IP routing table, which consists of destination address/next hop pairs, is used to enable dynamic routing. An entry in this table, for example, would be interpreted as follows: to get to network 172.31.0.0, send the packet out Ethernet interface 0 (E0). IP routing specifies that IP datagrams travel through internetworks one hop at a time. The entire route is not known at the onset of the journey, however. Instead, at each stop, the next destination is calculated by matching the destination address within the datagram with an entry in the current node's routing table. Each node's involvement in the routing process is limited to forwarding packets based on internal information. The nodes do not monitor whether the packets get to their final destination, nor does IP provide for error reporting back to the source when routing anomalies occur. This task is left to another Internet protocol, the Internet Control-Message Protocol (ICMP), which is discussed in the following section. Internet Control Message Protocol (ICMP) The Internet Control Message Protocol (ICMP) is a network-layer Internet protocol that provides message packets to report errors and other information regarding IP packet processing back to the source. ICMP is documented in RFC 792. ICMP Messages ICMPs generate several kinds of useful messages, including Destination Unreachable, Echo Request and Reply, Redirect, Time Exceeded, and Router Advertisement and Router Solicitation. If an ICMP message cannot be delivered, no second one is generated. This is to avoid an endless flood of ICMP messages. When an ICMP destination-unreachable message is sent by a router, it means that the router is unable to send the package to its final destination. The router then discards the original packet. Two reasons exist for why a destination might be unreachable. Most commonly, the source host has specified a nonexistent address. Less frequently, the router does not have a route to the destination. Destination-unreachable messages include four basic types: network unreachable, host unreachable, protocol unreachable, and port unreachable. Network-unreachable messages usually mean that a failure has occurred in the routing or addressing of a packet. Host-unreachable messages usually indicates delivery failure, such as a wrong subnet mask. Protocol-unreachable messages generally mean that the destination does not support the upper-layer protocol specified in the packet. Port-unreachable messages imply that the TCP socket or port is not available. An ICMP echo-request message, which is generated by the ping command, is sent by any host to test node reachability across an internetwork. The ICMP echo-reply message indicates that the node can be successfully reached. An ICMP Redirect message is sent by the router to the source host to stimulate more efficient routing. The router still forwards the original packet to the destination. ICMP redirects allow host routing tables to remain small because it is necessary to know the address of only one router, even if that router does not provide the best path. Even after receiving an ICMP Redirect message, some devices might continue using the less-efficient route. An ICMP Time-exceeded message is sent by the router if an IP packet's Time-to-Live field (expressed in hops or seconds) reaches zero. The Time-to-Live field prevents packets from continuously circulating the internetwork if the internetwork contains a routing loop. The router then discards the original packet.

ICMP Router-Discovery Protocol (IDRP) IDRP uses Router-Advertisement and Router-Solicitation messages to discover the addresses of routers on directly attached subnets. Each router periodically multicasts Router-Advertisement messages from each of its interfaces. Hosts then discover addresses of routers on directly attached subnets by listening for these messages. Hosts can use Router-Solicitation messages to request immediate advertisements rather than waiting for unsolicited messages. IRDP offers several advantages over other methods of discovering addresses of neighboring routers. Primarily, it does not require hosts to recognize routing protocols, nor does it require manual configuration by an administrator. Router-Advertisement messages enable hosts to discover the existence of neighboring routers, but not which router is best to reach a particular destination. If a host uses a poor first-hop router to reach a particular destination, it receives a Redirect message identifying a better choice.

Transmission Control Protocol (TCP) The TCP provides reliable transmission of data in an IP environment. TCP corresponds to the transport layer (Layer 4) of the OSI reference model. Among the services TCP provides are stream data transfer, reliability, efficient flow control, full-duplex operation, and multiplexing. With stream data transfer, TCP delivers an unstructured stream of bytes identified by sequence numbers. This service benefits applications because they do not have to chop data into blocks before handing it off to TCP. Instead, TCP groups bytes into segments and passes them to IP for delivery. TCP offers reliability by providing connection-oriented, end-to-end reliable packet delivery through an internetwork. It does this by sequencing bytes with a forwarding acknowledgment number that indicates to the destination the next byte the source expects to receive. Bytes not acknowledged within a specified time period are retransmitted. The reliability mechanism of TCP allows devices to deal with lost, delayed, duplicate, or misread packets. A time-out mechanism allows devices to detect lost packets and request retransmission. TCP offers efficient flow control, which means that, when sending acknowledgments back to the source, the receiving TCP process indicates the highest sequence number it can receive without overflowing its internal buffers. Full-duplex operation means that TCP processes can both send and receive at the same time. Finally, TCP's multiplexing means that numerous simultaneous upper-layer conversations can be multiplexed over a single connection.

TCP Connection Establishment To use reliable transport services, TCP hosts must establish a connection-oriented session with one another. Connection establishment is performed by using a "three-way handshake" mechanism. A three-way handshake synchronizes both ends of a connection by allowing both sides to agree upon initial sequence numbers. This mechanism also guarantees that both sides are ready to transmit data and know that the other side is ready to transmit as well. This is necessary so that packets are not transmitted or retransmitted during session establishment or after session termination. Each host randomly chooses a sequence number used to track bytes within the stream it is sending and receiving. Then, the three-way handshake proceeds in the following manner: The first host (Host A) initiates a connection by sending a packet with the initial sequence number (X) and SYN bit set to indicate a connection request. The second host (HostB) receives the SYN, records the sequence number X, and replies by acknowledging the SYN (with an ACK = X + 1). HostB includes its own initial sequence number (SEQ = Y). An ACK = 20 means the host has received bytes 0 through 19 and expects byte 20 next. This technique is called forward acknowledgment. Host A then acknowledges all bytes Host B sent with a forward acknowledgment indicating the next byte Host A expects to receive (ACK = Y + 1). Data transfer then can begin.

TCP Sliding Window A TCP sliding window provides more efficient use of network bandwidth than PAR because it enables hosts to send multiple bytes or packets before waiting for an acknowledgment. In TCP, the receiver specifies the current window size in every packet. Because TCP provides a byte-stream connection, window sizes are expressed in bytes. This means that a window is the number of data bytes that the sender is allowed to send before waiting for an acknowledgment. Initial window sizes are indicated at connection setup, but might vary throughout the data transfer to provide flow control. A window size of zero, for instance, means "Send no data." In a TCP sliding-window operation, for example, the sender might have a sequence of bytes to send (numbered 1 to 10) to a receiver who has a window size of five. The sender then would place a window around the first five bytes and transmit them together. It would then wait for an acknowledgment. The receiver would respond with an ACK = 6, indicating that it has received bytes 1 to 5 and is expecting byte 6 next. In the same packet, the receiver would indicate that its window size is 5. The sender then would move the sliding window five bytes to the right and transmit bytes 6 to 10. The receiver would respond with an ACK = 11, indicating that it is expecting sequenced byte 11 next. In this packet, the receiver might indicate that its window size is 0 (because, for example, its internal buffers are full). At this point, the sender cannot send any more bytes until the receiver sends another packet with a window size greater than 0.

TCP Packet Format illustrates the fields and overall format of a TCP packet. Figure30-10 Twelve fields comprise a TCP packet.

TCP Packet Field Descriptions The following descriptions summarize the TCP packet fields illustrated in : Source Port and Destination PortIdentifies points at which upper-layer source and destination processes receive TCP services. Sequence NumberUsually specifies the number assigned to the first byte of data in the current message. In the connection-establishment phase, this field also can be used to identify an initial sequence number to be used in an upcoming transmission. Acknowledgment NumberContains the sequence number of the next byte of data the sender of the packet expects to receive. Data OffsetIndicates the number of 32-bit words in the TCP header. ReservedRemains reserved for future use. FlagsCarries a variety of control information, including the SYN and ACK bits used for connection establishment, and the FIN bit used for connection termination. WindowSpecifies the size of the sender's receive window (that is, the buffer space available for incoming data). ChecksumIndicates whether the header was damaged in transit. Urgent PointerPoints to the first urgent data byte in the packet. OptionsSpecifies various TCP options. DataContains upper-layer information. User Datagram Protocol (UDP) The User Datagram Protocol (UDP) is a connectionless transport-layer protocol (Layer 4) that belongs to the Internet protocol family. UDP is basically an interface between IP and upper-layer processes. UDP protocol ports distinguish multiple applications running on a single device from one another. Unlike the TCP, UDP adds no reliability, flow-control, or error-recovery functions to IP. Because of UDP's simplicity, UDP headers contain fewer bytes and consume less network overhead than TCP. UDP is useful in situations where the reliability mechanisms of TCP are not necessary, such as in cases where a higher-layer protocol might provide error and flow control. UDP is the transport protocol for several well-known application-layer protocols, including Network File System (NFS), Simple Network Management Protocol (SNMP), Domain Name System (DNS), and Trivial File Transfer Protocol (TFTP). The UDP packet format contains four fields, as shown in . These include source and destination ports, length, and checksum fields. Figure30-11 A UDP packet consists of four fields.

Source and destination ports contain the 16-bit UDP protocol port numbers used to demultiplex datagrams for receiving application-layer processes. A length field specifies the length of the UDP header and data. Checksum provides an (optional) integrity check on the UDP header and data. Internet Protocols Application-Layer Protocols The Internet protocol suite includes many application-layer protocols that represent a wide variety of applications, including the following: File Transfer Protocol (FTP)Moves files between devices Simple Network-Management Protocol (SNMP)Primarily reports anomalous network conditions and sets network threshold values TelnetServes as a terminal emulation protocol X WindowsServes as a distributed windowing and graphics system used for communication between X terminals and UNIX workstations Network File System (NFS), External Data Representation (XDR), and Remote Procedure Call (RPC)Work together to enable transparent access to remote network resources Simple Mail Transfer Protocol (SMTP)Provides electronic mail services Domain Name System (DNS)Translates the names of network nodes into network addresses

lists these higher-layer protocols and the applications that they support. Table30-5 Higher-Layer Protocols and Their Applications Application Protocols

File transfer FTP

Terminal emulation Telnet

Electronic mail SMTP

Network management SNMP

Distributed file services NFS, XDR, RPC, X Windows

Internet Protocol IPIP Addressing First Octet Rage - XXXX.xxxx.xxxx.xxxxXXXX = Class of the IP addressIP Address is equal to 32 bytes broken down in to 4 OCTETS of 8 bytes (4*8=32) 8 bytes. 8bytes. 8bytes. 8bytesEx: 130.23120.35The IP address is broken down into 2/3 parts NETWORK, SUBNETWORK, and HOSTsNetwork part can be one of three types:CLASS A- Network with a range of1.0.0.0 to 126.0.0.0CLASS B- Network with a range of128.0.0.0 to 191.254.0.0CLASS C- Network with a range of192.0.1.0 to 223.255.254.0

When Subnetting a Network, A third part of an IP address appears in the middle of the address- Namely the SUBNET part of the address. This field is created by stealing or borrowing bits form the host part of the address. The size of the network part of the address never shrinks- In other words, Class A,B and C rules still apply when defining the size of the network part of the address. The host part of the address shrinks to make room for the subnet part of the address.The x^x 2 represents the two reserved IP address that cannot be used as an IP address the Broadcast subnet and the Zero subnet address. Both for the HOST address and the Subnetwok.One reserved subnet, the subnet that has all binary 0sClass A network ex: 45.125.0(binary -0000000).25In the subnet field, is called ZERO-SUBNET. The subnet with all binary 1s is the subnet field called the Broadcast Subnet and it is also reserved.

The Mask is a 32 bit binary number usually written in dotted-decimal format. The purpose of the mask is to define the structure of an IP address.Class A network ex: 45.125.256 (binary 1111111).25 IP address = 32 bits or 8 bytes

Four OCTETS make up the address with each OCTET = 8bytes or 32 bitsIP address: 1111111.00000000.00000000.11111111Or : 255.0.0.255Based on the size to the NETWORK you will know how many host bits you have to work with.Broadcast address 255.255.255.256Reserved IP address networks are0.0.0.0 Used as a broadcast address 127.0.0.0 - Loop back address128.0.0.0191.255.0.0192.0.0.0223.255.255.0Are all reserved and cannot be used in the public network.CLASS A Network with a range ofIP Range 1.0.0.0 to 126.0.0.0Number of Networks of this Class 2^7 2 Number of Hosts per Network 2^24 2Size of the Network Part of the address (bytes)1 byte or 8 bits Size of the Host Pat of Address (bytes) 3 bytes or 24 bitsDefault Mask for A Class network255.0.0.0

CLASS B Network with a range ofIP Range128.0.0.0 to 191.254.0.0Number of Networks of this Class 2^14 2 Number of Hosts per Network 2^16 2Size of the Network Part of the address (bytes)2 byte or 16 bits Size of the Host Pat of Address (bytes) 2 bytes or 16 bitsDefault Mask for A Class network255.255.0.0

CLASS C Network with a range ofIP Range 192.0.1.0 to 223.255.254.0Number of Networks of this Class 2^21 2 Number of Hosts per Network 2^8 2Size of the Network Part of the address (bytes)3 byte or 8 bits Size of the Host Pat of Address (bytes) 1 bytes or 24 bitsDefault Mask for A Class network255.255.255.0Broadcast address 255.255.255.256Converting IP Address from Decimal to Binary and back againBinary (0 or 1) =11111111Conversion Table1286432168421Binary Format =11111111Decimal format = 256Every OCTET must be compared to the table to produce a decimal value.

The Boolean AND operationA Boolean AND is a math operation performed to a pair of one-digit binary numbers. The result is another one-digit binary number. 0 AND 0 Yields a 00 AND 1 Yields a 01 AND 0 Yields a 01 AND 1 Yields a 1

To discover the Subnet Number in which a particular IP address resides, you perform a BITWISE AND between the IP address and the SUBNET MASK.Decimal ValueBinary Value

Address 150.150.2.110010110100101100000001000000001Mask 255.255.255.011111111111111111111111100000000Result 150.150.2.010010110100101100000001000000000

The Result is the SUBNET NUMBER

Decimal to Binary CalculationBit Position87654321Bit Value1286432168421

Counting in Mask Possible values128+64+32+16+8+4+2+1||=======Possible values128192224240248252254255Calculation of Subnets values256 256 256 256 256 256 256 256 128-192-224-240-248-252-254-255128 64 32 16 8 4 2 1256128 64 32 16 8 4 2192 96 48 24 12 6 3256128 64 32 16 8 4160 80 40 20 10 5192 96 48 24 12 6 224 112 56 28 14 7256 128 64 32 16 8 144 72 36 18 9160 80 40 20 10|| || || || ||Last Possible Values256 256 256 256 256

Prefix NotationTo understand prefix notation it is important to know that all subnet masks have some number of consecutive binary 1s, followed by binary 0s. In other words, a subnet mast cannot have 1s and 0s interspersed thought the mask- the makes always has some number of binary 1s followed by binary 0s.Prefix notation is simply denotes the number of binary 1s in a mask, preceded by a /. In other words, for subnet mask 255.255.255.0 = 11111111.1111111.1111111.00000000 = /24 in Prefix notation.24 represent the 24 consecutive 1s in the mask address. (8*3 = 24)255.255.0.0 = /16255.0.0.0 =/8IP addressNumber ofNumber ofClass/Networks NetworksHostsSubnet Mask Host bitsA1-1262^7 -22^24-2255.0.0.0 24 (2^24)B128-1912^14 22^14- 2255.255.0.0 16C192-2232^24-22^8-2255.255.255.0 8D224-239MulticastingE240-254Test network Computer uses the mask to define the size of the network.

Counting in binary 2^ =1,2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4056 2^4 = 162^8 = 256*maximum value for a mask is 255. 256 is the broadcast value.Reserved Address0000.0000.0000.0000 - reserved0.0.0.0 Broadcast Address (Zero Subnet)1.1.1.1Broadcast subnet127.0.0.0Loop back Address128.0.0.0 Reserved191.255.0.0Reserved192.0.0.0Reserved223.255.255.255 ReservedPrivate Address10.0.0.0 - 10.255.255.2558172.16.0.0 172.31.255.25512192.168.0.0 -192.168.255.25516

Mask is a 32 bit binary number255.255 .255.08bits.8bits.8bits.8.bits = 32 bitsMask Brake downPlace Value for Binary 128, 64, 32,16,8,4,2,18bits16bits24bits32bits255.255.255.255

Decimal to Binary conversion Calculation with Mask ValuesDecimalBinaryBits00000 0000 0 1281000 00001=256-128=128 hosts per subnet1921100 00002=256-192=64 Hosts per subnet2241110 00003=256-224=32 Hosts per subnet2401111 00004=256-240=16 Hosts per subnet2481111 10005=256-248=8 Hosts per subnet2521111 11006=256-252=4 Hosts per subnet2541111 11107=256-254=2 Hosts per subnet2551111 11118=256-255=1 Hosts per subnet

HOW MANY HOSTS and HOW MANY SUBNETSThe following facts tell you how to find the sizes of the network, subnet, and host parts of an IP address: The network part of the address always is defined by class rules.

The host pat of the address always is defined by the mask: binary 0s in the mask mean that the corresponding address bits are part of the host field.

The subnet part of the address is whats left over in the 32-bit address.

To find the amount of HOSTs and SUBNETs BITS1) Get the IP address 8.1.4.5 (Class A network)2) Get the MASK 255.255.0.0 = 1111111.1111111.00000000.0000000 (16 bits)3) Number of Network BITS = Class A network has 8 bits Defined by Network Class4) Number of Host Bits = Class A networks has 16 HOST BITS1) Number of SUBNETS = 8

32 network size bits 8 + Host size bits 16 =

32 (8 + 16) = 32- 24 = 8 bits

Number of network bits 8Number of host bits 16Number of subnet bits 8

INTERESTING MASK is a (Non 255 default value for mask)IP Address: 130.4.102.1MASK: 255.255.252.0CLASS B Network with a range ofThe number of host bits implied by a mask becomes more apparent after converting the mask to binary. In the first mask 255.255.252.0 there are ten binary 0sDecimal 255.255.252.0Convert to binaryBinary11111111.1111111.11111100.00000000 (252)Implying a 10 bit host field.Because that mask is used with a Class B address (130.4.102.1), implying 16 network bits, there are 6 remaining subnet bits. The class rules define the network part

The mask binary 0s define the host part

Whats left over defines the size of the subnet part

Binary11111111.1111111.11111100.0000000016 bits network -6 remaining subnet bits- 10 bit host field

Chart to know 1 Decimal and Binary Values in a Single Octet of a Valid Subnet MaskDecimal ValueBinary Value00000 00001281000 00001921100 00002241110 00002401111 00002481111 10002521111 11002541111 11102551111 1111

To find the subnet a IP address is a part of:1) Get the ip address

IP Address:130. 4.102.1 and Subnet Mask 255.255.252.0

2) Find the interesting mask 255.255.252.0 ( any number not 255)

3) Subtract the interesting (252) octet from 256

256- 252 = 4 (which is the Magic number) 4) Divide the corresponding interesting matching octave with to the magic number:102 / 4 = 25 Then take the result and multiply it by the magic number25 * 4 = 100 This give you the subnet that ip address in.4) To find the subnet value just put a zero at the end of new address130.4.100.0 (Subnet number)Add one to the Subnet number and that will give you the First Valid IP address:130.4.100.1 (First Valid IP address in the subnet)Broadcast address is calculated by Subtracting 1 away from the next valid IP address:130.4.100.0 +4 (Amount of subnets in that network)130.4.104.0 (Is the next subnet) -1130.4.103.255 (Broadcast address for the 130.4.100.0 Network) Network bits are all 1s 1111 1111.1111 1111.1111 1111.0 Host bits are all 0s 11111111.00000000.00000000.00000000 255 is the last valid address in any type of network 256 is not used.

GIVEN THE IP ADDRESS AND MASK, HOW MANY SUBNETS ARE THERE? And how many hosts are there is a single subnet?Calculations:Number of SUBNETS = 2^number of subnets bits 2(Based on whether or not it is ClassFull or ClassLess)Number of Host = 2^number of host bits - 2STEP 1 Identify the structure of the IP addressIP Address 8.1.4.5 /16STEP 2- Identify the size of the network part of the address, based on Class A,B and C rulesThis is a Class A network = 8 bitsSTEP 3 Identify the size of the host part of the address, based on the number of binary 0s in the mask. If the mask is tricky, us the chart of typical mask values to convert the mask to binary more quickly. 255.255.0.0 Or /16 = 1111 1111.1111 1111.0000 0000.0000 0000Host is equal to 16 bits (16 0s)STEP 4 The size of the subnet part is whats left over; mathematically, it is 32- (Number of network bits+ Host Bits)32 (8 + 16) = 8Size of the Subnet Part is = 8 bits STEP 5 Declare the number of subnets, which is 2^ (number of subnets) 2= 2^8 2 = 254STEP 6 Declare the number of host per subnet, which is 2^ (number of host bits) 2= 2^16 2 = 65,534

GIVEN THE IP ADDRESS AND MASK, HOW MANY SUBNETS ARE THERE? And how many hosts are there is a single subnet?1) IP Address: 130.4.102.1 / 22/22 = 1111 1111.1111 1111.1111 1100.0000 0000 or 255.255.252.02)Class B Network 3)Network Bits 16Host 104)32 (16 + 10) = 6 bits for SUBNET5)2^6 - 2 = 62 Number of SUBNETS2) 2^10 2 = 1022 HOSTs

Finding the SUBNET BROADCAST ADDRESSThe SUBNET BROADCAST address, sometimes called the DIRECTED BROADCATS ADDRESS, can be used to send a packet to every device in a single subnet. However, few tools and protocols use the subnet address anymore. How ever by calculating the subnet broadcast address, you easily can calculate the largest valid IP address in the subnet, which is important part of answering Subnetting questions.There is a binary math operation to calculate the subnet broadcast address. However, there is a much easier process, especially if you already have the subnet number in binary:Change all the HOST bit values in the subnet number to binary 1s.DecimalBinaryIP Address 199.1.1.100 =1100 0111.0000 0001.0000 0001.0110 0100Mask255.255.255.0 =1111 1111.1111.1111.1111 1111.0000 0000SubnetAND Result 199.1.1.0 =1100 0111.0000.0001.0000.0001.0000 0000Broadcast 199.1.1.255 = 1100 0111.0000 0001.0000 0001.1111 1111

FINDING THE RANGE OF VALID IP ADDRESS IN A SUBNETThe SUBNET number is the numerically smallest number in the subnet, and the broadcast address is the numerically largest number. So, the rang of valid IP addresses starts with one more than the SUBNET number and ends with the address that is one less than the broadcast address.DecimalBinaryIP Address 199.1.1.100 =1100 0111.0000 0001.0000 0001.0110 0100Mask255.255.255.0 =1111 1111.1111.1111.1111 1111.0000 0000SubnetAND Result 199.1.1.0 =1100 0111.0000.0001.0000.0001.0000 0000First address 199.1.1.1 = ( + 1 to the subnet address)Broadcast 199.1.1.255 = 1100 0111.0000 0001.0000 0001.1111 1111LAST Address 199.1.1.254 (-1 from the Broadcast address)Easier Math with Easy MasksOf all the possible subnet masks, three mask,255.0.0.0255.255.0.0 255.255.255.0 These are called easy masks because you can find the subnet number and broadcast address easily, without any real math tricks. In fact, of the theses three masks, 255.0.0.0 does not actually case any Subnetting. So, this section worries about only how to use the two easy masks that can be used for Subnetting.255.255.0.0 or 255.255.255.0, do the following:Step 1 Copy the first tow (mask 255.255.0.0) or the first three (mask 255.255.255.0) octets for the original IP address.Step 2 Write down 0s in the last two octets (mask 255.255.0.0) or the last octet (mask 255.255.255.0).Finding the subnet broadcast address is just as easy:Do the same thing that you did for finding the SUBNET, but instead of writhing down 0s in the last octet or two, write down 255s.When you know the subnet number and the broadcast address, you easily can find the first and the last IP addresses in the subnet, using the same simple logic covered earlier: To find the first valid IP address in the subnet, copy the subnet numbers, but add 1 to the fourth octet.

To find the last valid IP address in the subnet, copy the broadcast address, but subtract 1 from the fourth octet.

Easier Math with Difficult MasksWhen the subnet mask is not 255.255.0.0 or 255.255, these are considered Difficult Mask.The following Process help you find the SUBNET number and BROADCAST address without binary math when using a difficult mask.The unusual part of this shortcut begins when you draw a box around the interesting octet in the table. The interesting octet is a mask octet that is not 255 or 0 it is called the interesting octet because it is the one which give the most problems. First you put in the IP address and the mask. Next you should complete the chart for everything to the left of the box. To complete the chart, look at the original I address octets to the left of the box, and copy those into the subnet, first valid address, broadcast, and last valid address fields. Not that only octets fully to the left of the box should be copied- the interesting octet, which is inside the box, should not be copied.

To find the subnet number the first step is easy. In the SUBNET number, for any octets fully to the right of the box, write down a 0. That should leave you with one octet of the subnet number missing- the interesting octetNext comes the tricky part of this shortcut, which gives tyou the value of the SUBNET NUMBER in the interesting octet.First, you find the MAGIC NUMBER which is =256 (The mask INTERESTING OCTET)Or for this question256 252 = 4 (MAGIC NUMBER)Then you find the multiple of the magic number that is the closest to the address interesting octet, and this multiple is less that or equal to 102.4 * 25 = 100 < 102 or 102 / 4 = 25.5 rounding give you 25 * 4 = 100So the Subnet number is equal to 100Steps for finding the SUBNET Networks Step 1 Find the magic number, which is 256 the value of the masks interesting octet.

Step 2 Find the multiple of the magic number that is closet to, but not greater than the address interesting octet.

Step 3 Write down the multiple of the magic number as the value of the subnet numbers interesting octet.

The magic number is 256 minus the masks interesting octet. In this case, you have 256 -252, or a magic number of 4. Then you add the magic number to the interesting octet value of the subnet number and subtract 1. The result is the broadcast addresss value in the interesting octet.

100 + 4 (magic number) 1 = 103 (Gives you the BROADCAST ADDRESS)

When you know the broadcast address, you easily can find the last valid IP address in the subnet:

To find the last valid IP address in the subnet, copy the broadcast address, but subtract 1 form the fourth octet.

To find the broadcast addresss interesting octet value, take the subnet numbers interesting octet value, add the magic number, and subtract 1.

Step 1 Create and complete the easy parts of the subnet chart Create a generic subnet chart. Write down the iP address and subnet mask in the first two rows of the chart. Draw a box around the column of the interesting octet Copy the address octets to the left of the line or the box ion into the final four rows of the chart.

Step 2 Derive the subnet number and the first valid IP address. Write down 0s in the subnet number for the octets to the right of the box. Find the magic number, which is 256 minus the value of the masks interesting octet.

Find the multiple of the magic number that is closet to but not greater that the addresss interesting octet.

Write down that multiple of the magic number as the value for the subnet numbers interesting octet.

To find the first valid IP address in the subnet, copy the subnet number, but add 1 to the fourth octet.

Step 3 Derive the broadcast address and the last valid IP address. Write down 255 in the broadcast address octet to the right of the ling or the box

To find the broadcast addresss interesting octet value, take the subnet number interesting octet value, add the magic umber, and subtract 1.

To find the last valid IP address in the subnet, copy the broadcast address, but subtract 1 form the fourth octet.

What Subnet Masks Meet the Stated Design Requirements?Your are using a Class B network x, and your need to have 200 subnets, with at most 200 host per subnet. Which of the following subnets masks can be used? To find the correct answer to these types of question, you first need to decide how may subnets bits and host bits you need to meet the requirements. Basically, the number of hosts per subnet is 2^x 2 where x is the number of host bits in the address. Likewise, the number of subnets of a network, assuming that the same subnet mask is used all over the network, is bits and shot bits are required, you can figure out what mask, or mask, meet the stated design goals in the question.Examples : Your network can use Class B network 130.1.0.0 what subnet masks meet the requirement that you plan to allow at most 200 subnets, with at most 200 hosts per subnet?First you need to figure out how many subnet bits allow for 200 subnet. You simply can use the formula 2^x 2 and plug in values for x, until one of the number is at least 200. In this case, x turns out to be 8 in other words, you need at least 8 subnet bits to allow for 200 subnets.

Number of bits inMaximum Number of the host or subnet fieldHost of Subnets (2^x 2)xCheckX=10(2^1- 2 =0)X=22(2^2 - 2 = 2)X=36 ( 2^3 -2 = 6)X=414 (2 ^4 - 2 = 14)X=530 (2^5- 2 = 30)X=662 (2 ^6 - 2 = 60)X=7126 (2^7 - 2 = 126)X=8*******254 (2^8 - 2 = 254)X=9510 (2^9 - 2 = 510)X=101,022 (2^10 - 2 = 1,022)X=112,046 (2^11 - 2 = 2,046)X=124,094(2^12 - 2 = 2,046)X=138,190(2^13 - 2 = 8,190)X=1416,382(2^14 - 2 = 16,382) 2^X-2 = XXX or 2^X IS ONLY USED TO DETERMIN WEATHER OR NOT TO USE THE ZEOR SUBNET. DEFINED WHEN THE ROUTING PROTOCOL IS USED ClassLess or ClassFull. IT will tell you weather or not you can use a SUBNET. The Host Calculation will never change 2^x-2= xxxx

7 subnet bits are not enough because that allows for only 126 subnets. You need 8 subnet bits, and similarly, because your need up to 200 hosts per subnet, you need 8 host bits.2^8 2 = 254 ( with 8 subnet bits gives you 254 hosts)2^7 2 = 126 ( with 7 subnet bits gives you 126 hosts)Finally, you need to decide somehow what mask(s) to use, knowing that you have Class B network and that you must have at least 8 subnet bits and 8 host bits. Using the letter N to represent network bits, the letter S to represent subnet bits, and the letter H to represent host bits, the following test shows the size of the various fields.NNNN NNNN.NNNN NNNN.SSSS SSSS. HHHH HHHHAll that is let is to derive the actual subnet mask. Because you need 8 bits for the subnet field and 8 for the host field, and the network field takes up to 16 bits, you already have allocated all 32 bits of the address structure. So, only one possible subnet mask works. To figure out the mask, you need to write down the 32-bit subnet mask, applying the following fact and subnet masks Subnet bits in a subnet mask are, by definition, all binary 1sSimilarly, The host bits in a subnet mask are, by definition, all binary 0s.So, the only valid subnet masks, in binary; is this1111 1111.1111 1111.1111 1111.0000 0000When converted to Decimal, this is 255.255.255.0Your network can use Class B network 130.1.0.0. What subnet masks meet the requirement that you plan to allow at most 50 subnets, what at most 200 host per subnetFor this design, you still need at least 8 host bits, but now you need only at least 6 subnet bits. Six subnet bits would allow for 2^6 2 = 62 (closes to 50 subnets), subnets. Following the same conversion as before, but now using an x for bits that can either subnet or host bits, the format of address structure work be as follows:NNNN NNNN.NNNN NNNN.SSSS SSXX.HHHH HHHH

In other words, the address will have 16 network bits, at least 6 subnet bits, and at least 8 host bits. This example actually allows for three valid subnet masks, whose structure is as follows:8 subnet, 8 hosts BITSNNNN NNNN.NNNN NNNN.SSSS SSSS.HHHH HHHH1111 1111.1111 1111.1111 1111.0000 0000Binary = 255.255.255.07 SUBNET, 9 HOSTS BITSNNNN NNNN.NNNN NNNN.SSSS SSsH.HHHH HHHH1111 1111.1111 1111.1111 1110.0000 0000BINARY = 255.255.2546 SUBNET, 10 HOST BITSNNNN NNNN.NNNN NNNN.SSSS SSHH.HHHH HHHH1111 1111.1111 1111.1111 1111.0000 0000BINARY = 255.255.252.0

What are the other SUBNET numbers? First the question needs a better definition or at least, a more complete one. The question might be better stated like this;If the same subnet mask is used for all subnets of this Class A,B, or C network, what are the valid subnets?IP design conversions do not require the engineer to use the same mask for every subnet. Unless specifically stated, the question : What are all the subnets? Probably assumes that the same mask is used for all subnets, unless the question specifically state that different mask can be used on different subnets.

The three Step process for finding the other subnet values.Three-Step process Generic Subnet List Chart.

Check-- 8 SUBNET BITS = 2^6 2 = 62 AND 248 / 4 = 6262 SUBNETS SHOULD BE CONFIGURED.1) Write down the Network IP address number and subnet mask in the first two rows for the subnet list chart.

2) Write down the network number in the third row. This is the zero subnet. Which is one of the two reserved subnets.

3) Do the follow two tasks, stopping when the next number that you would write down is the interesting column is 256.

a. Copy three non-interesting octets form the previous line.

b. Add the magic number to the previous interesting octet, and write that down as the value for the interesting octet.

IP Routing and SubnetsThis article describes the basics of IP routing. We will consider the example of a simple network and trace the life of a packet as it gets routed from one node to another. The routing tables at each node will be discussed.Before we go into depth of IP routing, we need to understand IP addresses. This is covered in the next section.IP Address ClassificationIP addresses are 32 bit integers which are represented in the familiar dot based notation. The dot based notation is nothing but a decimal representation for each byte of the IP address. For example, an IP address with a hex value of 0x800A080B is represented as 128.10.8.11.The internet, as the name suggests, is a network of networks. Thus to uniquely identify a host on the internet, one needs to know the network's id and the host's id in the network. Thus IP address consist of two components, the network id and the host id. The network id is the number assigned to a network in the internet. Host id represents the id assigned to a host in the network.The figure below shows different classes of IP addresses. These addresses differ in the number of bits assigned to the network and host ids. Different classes of addresses serve different needs. For example, a class A IP address is suitable when the internet consists of a small number of networks but each network consists of a large number of hosts. On the other extreme, class C addressing is suitable for internets with a very large number of networks, with a small number of hosts per network.

An Example InternetSubnetsThe figure below describes a small internet consisting of three networks 128.8, 128.9.1 and 128.9.2. Strictly speaking, the internet consists of 128.8 network and 128.9.1 and 128.9.2 sub-networks (subnets). As we have seen in the previous section, 128.8 and 128.9 should have been classified as the network portion of a class B IP address. In this network 128.9 has been divided into two sub-networks (128.9.1 and 128.9.2) by using one of the bytes of the two byte host id as sub-network id.Another way to look at this is that the first three bytes of IP addresses in 128.9.1 and 128.9.2 subnets are used for routing the packet. The other bits in the IP address are don't care from routing point of view. The specification of bits that should be used for routing is specified by associating a subnet mask with a routing entry. In this example, the subnet mask is 255.255.255.0 (0xFFFFFF00).IP RoutingNetworks in the internet are connected to each other via routers. Routers carry traffic from one network/subnet to another. Routers maintain a routing table to decide how to route the IP packets. Each routing entry consists of the destination address, subnet mask and "route to" field. When a message needs to be routed to an IP address, the following steps are followed:1. The destination IP address is masked with the subnet mask and then compared with the destination field for all entries in the routing table. 2. This comparison may yield a match with more than one entry the entry with the longest subnet mask will be selected. E.g. , a packet destined for 128.8.1.2 reaching Host A would match the entries corresponding to 128.8.1.2 and 128.8.0. The entry corresponding to 128.8.1.2 will be selected, as it has a longer subnet mask. 3. Once an entry has been selected, the "route to" field is consulted and the action taken depends on the contents of this field: If the "route to" field contains SELF the packet is meant for this node. The IP packet is passed to the OS for application processing If the "route to" field contains a LAN interface id, the packet is destined for a LAN that is directly connected to the router/host. In this case, the packet is routed directly on the LAN. If the "route to" field contains an IP address, the packet is forwarded to the IP address specified. Further routing of the packet will be carried out by the specified IP address. Note: IP routing also supports a default entry. If the packet does not match any other entry, it is routed according to the default entry.

Multiple IP AddressesAnother important aspect of internets is a node in the internet can have multiple IP addresses. There will be one IP address per interface. For example, the Router in the figure above has three IP addresses, viz. 128.8.1.1, 128.9.1.1 and 128.9.2.1.

Routing of a Packet from Host A to Host CHere we will trace the path taken by an IP packet sent from Host A to Host C. Routing related fields in the Ethernet MAC header and IP header are shown.Host A originates an IP packet towards Host C1. Application sends a message to Host C by sending it to 128.9.2.2 IP address (Host C's IP address). 2. This IP address matches the entry corresponding to 128.9.0.0. The "route to" field for the selected entry contains another IP address - 128.8.1.1. This is the IP address of the Router. 3. The IP routing table is accessed again for 128.8.1.1. 4. The entry that matches 128.8.1.1 contains LAN 0 interface id. This specifies that the destination node is directly connected to the host. 5. This packet is passed to the device driver. 6. Device driver consults the ARP cache to identify the Ethernet MAC address corresponding to the 128.8.1.1. (ARP is covered in another article). 7. Ethernet frame is sent to the MAC address found by ARP. The packet sent on the 128.8 LAN is:Ethernet MAC HeaderIP Packet Payload

Destination MAC AddressSource MAC AddressDestination IP AddressSource IP AddressPayload

Router MAC AddressHost A MAC Address128.9.2.2128.8.1.2

Router send the IP packet to Host C1. Router receives the Ethernet frame and passes it to the IP layer. 2. IP routing table is consulted and a matching entry is found corresponding to 128.9.2 subnet. 3. Packet is routed on the LAN 2 interface. 4. Host C's MAC address is found from the ARP cache. 5. Ethernet frame is addressed to Host C MAC Address.

The packet sent over the 128.9.2 LAN is:Ethernet MAC HeaderIP Packet Payload

Destination MAC AddressSource MAC AddressDestination IP AddressSource IP AddressPayload

Host C MAC AddressRouter MAC Address128.9.2.2128.8.1.2

Host C receives the IP packet1. Host C receives the Ethernet frame and passes it to the IP layer. 2. IP routing table is searched and a match is detected with 128.9.2.2 entry. 3. The "route to" field contains SELF, so the message is passed to the higher layer for delivery to the application.

CIDR Classless Inter-domain Routing

NAT- Network addresses Translation.CIDR**********RFC 1817 - Which calls for (combine) or aggregating multiple network numbers into a single routing entity. Has to be consecutive network numbers.

Private AddressingRFC 1918 Some computer will never be connected to the internet. These computer IP addresses could be duplicates of registered IP address in the internet.Private Address Space RFC 1918Class Network10.0.0.0 to 10.255.255.255.255A172.16.0.0 to 172.31.255.255B192.168.0.0 to 192.168.255.255C

NATRFC 1631 Allows a host that does not have a valid registered IP address to communicate with other host through the Internet.NAT achieves its goals by using a valid registered IP address to represent the private address to the Rest of the Network.Types of NAT Static NAT one to one mapping with 254 static maps per IP outside address.

Dynamic NAT Automate mapping of IP Inside to Public addressing using a pool of IP address

PAT Overloading with Port Address Translation.

Cisco calls private IP addresses used In the INSIDE network is called the Inside Local And On the OUTSIDE or internet inside are called GLOBAL address

Terminology MeaningPrivate = Local or Inside addressPublic = GlobalOutside = InternetOutside public = Outside of the network.Outside global = or Internet ready IP address.Outside local = Internet IP address.

Outside NetworkPublic Network (Internet)Change to a INSIDE GLOBALIP address which is outside Routable.Inside NetworkPrivate NetworkPrivet IP addressINSIDE LOCALNot able to be routed out side. Private Router ISP PUBLIC Router

>------CHANGE ---------

10.1.1.2100.34.45.6The Source IP Address and Source Port (if the PORT is all ready used Only can be used ONE per PAT IP Address) has to change to an IP address which is GLOBALLY Routable. That is when NAT Changes the Inside Local to an Inside Global address. The Inside Global IP Address is what Web servers send back requested information to. The Inside Global Address is what the ISP sees since the serial link to the ISP interfaces are on the same Subnet. The web servers will send information to the Private Router Serial interface IP address which is Globally Routable.

Overloading with PAT Overloading allows NAT to scale to support many clients with only a few public IP address. This is based on each ip connection being supplied a port number during the communications. Nat uses the overload command to perform its functions. PAT Port addressing Translation can use more than 65,000 ports.

NAT ConfigurationStatic Commands:Router (config) # Int e0/0Router (config-int) # Ip address 10.1.1.3 255.255.255Router (config-int) # ip nat insideRouter (config) # Int s0/0Router (config-int) # Ip address 200.1.1.3 255.255.255Router (config-int) # ip Nat outside To Show the map of Inside and Outside IP mapping table.Command:>Router # Show ip Nat translations

PAT can use the same OUTSIDE Global IP ADDRESS for different computers IP Address but the Port number cannot be the same.

To show the Translations this means Source IP Address changed to a Global IP address table.Command:Router # Show IP NAT Translations

To show the connections how may time NAT was used Misses and Hits and Expired.Command:Router # Show ip NAT Statistics Dynamic NAT configurationsRouter # ip Nat inside ----------- Ethernet interface (LAN)Router# ip Nat outside ---------- Serial interface (WAN)Router# ip Nat pool Fred 200.1.1.1 200.1.1.2 255.255.255.252 ip Nat pool - command for dynamic nat configuration Fred access list named Fred 200.1.1.1 200.1.1.2 range of valid inside global address.

Router# Ip Nat pool FredRouter# Nat inside source list pool FredRouter# access list 1 permits 10.1.1.2Router# access list 1 permits 10.1.1.3Router# Clear IP NAT Translation Clears all mapping made in the routersRouter# debug IP NAT

NAT OVERLOAD configurations All the rest is the same except the Overload command which must be used.

Full command to use NAT once the Interfaces have been set up with IP NAT INSIDE and IP NAT Outside Commands.Router # IP NAT INSIDE / Source LIST ACL-number/Interface type-and-number overloadRouter# ip Nat inside source list 3 interface serial 0/1/0 over loadRouter # access-list 3 permit 172.22.0.0 0.0.255.255 (Permit ONLY =Access-List IP range must match to be able to use the NAT PAT Translations (UP to 65,000 translations for NAT PAT.)

To fine tune the balance of the traffic flow two commands are used:First The:# Variance X Command which means any additional routs to the same subnet with a metric lower then X it will be considered equal to the same metric as the route with the lowest metric.# Variance 4 command -----would mean metric 200 < 400 = 400The lowest metric is 400.Second the:Router# Traffic-Share min Command used by IGRP tells the router to only use the route which has the lowest metric when there are multiple routes to the same subnet. If this is not used the router will balance the traffic across multiple paths based on the metrics of the routs in the routing table. Metrics are generated by using Bandwidth and Delay in the calculation for the route metric.

Internet Control Message ProtocolTCP/IP includes a protocol specifically to help manage and control the operation of a TCP/IP network called the Internet Control Message Protocol (ICMP). The ICMP protocol provides a wide variety of information about the health and operation status of a network, Control Message is the most descriptive part of the name

ICMP - defines messages that helps control and manage the work of IP and, therefore, is considered to be part of TCP/IPs network layer. Because ICMP helps control IP, it can provide useful troubleshooting information.

In fact, the ICMP messages sit inside an IP packet, with no transport layer header at all so it is truly just an extension of the TCP/IP network layer.

ICMP defined - Occasionally a gateway (router) or destination host will communicate with a source host for example, to report an error in a datagram processing. For such purposes, this protocol, the Internet Control Message Protocol (ICMP, is used. ICMP uses the basic support of IP as if it were a higher level protocol; however, ICMP is actually an integral part of IP and must be implemented by every IP module.ICMP Message TypesMessage PurposeDestination unreachableThis tell the source host that there is a problem delivering a packet

Time exceededThe time that it takes a packet to be delivered has expired; the packet has been discarded.

RedirectThe router sending this message has received some packets for which another router would have had a better route; the message tell the sender to use the better route.

EchoThis is used by the ping command to verify connectivity.ICMP Echo Request and Echo ReplyThe ICMP echo request and echo reply messages are sent and received by the ping command. In Fact when people say that they sent a ping packet they really mean that they sent an ICMP echo request.

These two messages are very self-explanatory. The echo request simply means that the host to which it is addressed should reply to the packet. The echo reply is the ICMP message type that should be used in the reply.

The echo request includes some data that com be specified by the ping command; whatever data is sent in the echo request is sent back in the echo reply.

The ping command sends a packet to the stated destination address. The TCP/IP software at the destination then replies to the ping packet with a similar packet.

The ping command sends the first packet and waits for a response. If a response is received, the command displays an exclamation mark (!) If no response is received with in the the default timeout of 2 secons, the ping command displays a period(.).

The IOS ping command sends five of these packets by default.

We should look at a feature of the Cisco ping (and trace) command tat lets up specify a source address so that we can test connectivity form any interface. This is called the extended ping feature and work only in privilege mode. Basic ping will work in both user and privileges modes. The feature is implemented by typing ping at the prompt without a destination address. You then see a series of prompts offering choices. Extended Ping CommandsRouter# ping without any destination address this will give you additional Choices to chose the type of Ping and location you want to Ping from.Destination Unreachable ICMP messageThe ICMP Destination Unreachable message is sent when a message cannot be delivered completely to the application at the destination host. Because packet deliver can fail for many reasons, there are five separate unreachable function (codes) using this single ICMP unreachable message. All five code types pertain directly to an IP, TCP, or UDP feature.ICMP Unreachable codesUnreachable CodeWhen is it used What it typically is sent byNetwork UnreachableThere is no match in routing table RouterFor the packets destination

Host UnreachableThe packet can be routed to a routerRouterConnected to the destination subnet,But the host is not responding.

Cant fragmentThe packet has the Dont Fragment bitRouterset, and a router must fragment it to forward The packet.

Protocol unreachableThe packet is delivered to the destination Endpoint hostHost but, the transport layer protocol is not available that host.

Port unreachableThe packet is delivered to the destination Endpoint host Host, but the destination port has not been Opened by an application. One key to troubleshooting with the ping command is understanding the various codes the command uses to signify the various responses it can receive.

Codes that the ping Command is uses to signify the various responses it can receive.PingCommand CodeDescription!ICMP Echo Reply received.Nothing was received before the ping command timed out.UICMP unreachable (destination)NICMP unreachable (network) receivedPICMP unreachable (port) receivedQICMP source quench receivedMICMP Cant fragment messages received?Unknown packet received

IP Naming CommandsWhen using the IOS CLI, you will want to refer to names instead of IP addresses. Particularly for the trace, ping, and telnet commands, the IP address or host name nust be supplied. IOS can use statically configured name as well as refer to one or more DNSs.Command:Ip host mark 10.1.1.1Ip host Sam 10.23.23.45

CIDR*******CIDR is a convention defined in RFC 1817 that calls for aggregating multiple network numbers into a single routing entity. CIDR actually was created to help the scalability of the Internet router- imagine a router in the Internet with a route to every Class A,B, and C network on the planet! There are actually a little more than two million Class C networks alone! By aggregating the routes, Internet router have a significantly smaller number of routs in their routing tables.Priv