Internetworking With TCP/IP

IPv4 Addressing in

Ethernet, IEEE 802.3, Token Ring, X.25, SNA, FDDI, ….

TCP UDP

Telnet Gopher NFS

FTP X Win TFTP

SMTP SNMP

REXEC DNS RPC

Application Layer

Transport Layer

Network Layer

Link Interface

ICMP IGMPIP RARPARP

Parviz Kermani

Legends

Back to previous foil

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2IP Addressing

Acknowledgement

Part of the following pages were taken from materials provided by other authors and companies

CiscoLecture slides of “Computer Networking: A Top Down Approach” by Jim Kurose and Keith Ross“CCENT/CCNA ICND1 & 2- Official Exam Certification Guide”, Wendell Odom, Cisco Press

3IP Addressing

Internet in a Nutshell

Ethernet, IEEE 802.3, Token Ring, X.25, SNA, FDDI, ….

TCP UDP

Telnet Gopher NFS

FTP X Win TFTP

SMTP SNMP

REXEC DNS RPC

Application Layer

Transport Layer

Network Layer

Link Interface

ICMP IGMPIP RARPARP

4IP Addressing

Addresses & Names

Hardware (Layer 2)Lowest levelEthernet (MAC), Serial point-to-point, ..

Network (Layer 3)IPIPX, SNA, others

Application (layer 5?)Names (URL), alias, ..

All are important and neededUltimately, all deliveries move over the physical layerNote: Port address not under discussion (Transport)

5IP Addressing

Layer 2 Addressing

Uses MAC address Assigned to end devices

6IP Addressing

Layer 3 Addressing

Each Network Architecture has its own Layer 3 address format. OSI uses NSAP. TCP/IP uses IP

7IP Addressing

Host-to-Host Packet Delivery (1 of 10)

8IP Addressing

Host-to-Host Packet Delivery (2 of 10)

9IP Addressing

Host-to-Host Packet Delivery (3 of 10)

10IP Addressing

Host-to-Host Packet Delivery (4 of 10)

11IP Addressing

Host-to-Host Packet Delivery (5 of 10)

12IP Addressing

Host-to-Host Packet Delivery (6 of 10)

13IP Addressing

Host-to-Host Packet Delivery (7 of 10)

14IP Addressing

Host-to-Host Packet Delivery (8 of 10)

15IP Addressing

Host-to-Host Packet Delivery (9 of 10)

16IP Addressing

Host-to-Host Packet Delivery (10 of 10)

17IP Addressing

(Classical) IP Addressing (Layer 3)

IP address is 32 bitAn An IP address is broken in two parts

Network addressHost address

The division between network and host is determined by the size of network and determined by the “class” of the address

Network host

18IP Addressing

IP Addresses

“classful” addressing

0 network host

10 network host

110 network host

1110 multicast address

A

B

C

D

class1.0.0.0 to127.255.255.255

128.0.0.0 to191.255.255.255

192.0.0.0 to223.255.255.255

224.0.0.0 to239.255.255.255

32 bits

19IP Addressing

IP Addresses

IP Classful Addresses:Class A addresses begin with 0xxx, or 1 to 126 Class B addresses begin with 10xx, or 128 to 191 Class C addresses begin with 110x, or 192 to 223 Class D addresses begin with 1110, or 224 to 239

Multicast

Class E addresses begin with 1111, or 240 to 254Experimental

20IP Addressing

Classful Addressing

Number of elements in each class

Class Number of classes

Number of local addresses

A 0xxx 128 16,777,216B 10xx 16,384 65,534C 110x 2,097,152 254

21IP Addressing

Private IP Addresses Space

Private IP Networks Class of Network

Number of Networks

10.0.0.0 to 10.0.0.0 A 1172.16.0.0 to 172.31.0.0 B 16192.168.0.0 to 192.168.255.0 C 256

IP Addressing 22

Note: The third column is the Number of Networks (and not IP Addresses)

Problems with Classful Addressing

Inefficient use of address space, address space exhaustion

e.g., class B net allocated enough addresses for 65K hosts, even if only 2K hosts in that network

Network manageability (discussed below)No longer formally part of IP addressing architectureNote:

A classful address identifies the “Network” and “Host” field

No need for “Network Mask”!

23IP Addressing

Manageability: Flat Topology

ProblemsAll devices share the same bandwidth.All devices share the same broadcast domain.It is difficult to apply a security policy.

24IP Addressing

Manageability: Subnetworks

The Smaller networks are easier to manage.Overall traffic is reduced.You can more easily apply network security policies.

1-25IP Addressing

IP addressing: CIDRCIDR: Classless InterDomain Routing

Adopted by IETF in 1993Network (subnet) portion of address of arbitrary lengthaddress format: a.b.c.d/x, where x is # bits in network (subnet) portion of address

To support 2000 hosts, a block of 2048 addresses of the form a.b.c.d/21 assigned

11 bits needed to store 2048 (211=2048)In practice the 11 bit rightmost addressing could be further divided (subnetting, more on this later)

11001000 00010111 00010000 00000000

networkpart

hostpart

152.23.16.0/2126IP Addressing

Network Mask

With CIDR, address no longer specifies the network portionMask is used to extract network portion from an IP Address

A string of 32 bitsBits corresponding to network (and subnet) part set to ‘1’Bits corresponding to host part set to ‘0’Ex (classful address):

Addr = 9.2.225.65/8= 00001001.00000010.11100001.01000001

Mask = 11111111.00000000.00000000.00000000= 255 . 0 . 0 . 0

27IP Addressing

Mask examples (classful addresses)

Ex-1:Addr = 9 . 2 . 225 . 65/8

= 00001001.00000010.11100001.01000001Mask = 11111111.00000000.00000000.00000000

= 255 . 0 . 0 . 0N-Adr= 10001001.00000000.00000000.00000000

9.0.0.0

Ex-2Addr = 156 . 204 . 135 . 160/19

= 10011100.11001100.10000111.10100000Mask = 11111111.11111111.11100000.00000000

= 255 . 255 . 224 . 0N-Adr= 10011100.11001100.10000000.00000000

156 . 204 . 128 . 0

28IP Addressing

Two-Level and Three-Level Addresses

Inefficiency of two-level addressesA third level of addressing, consisting of subnets, was developedSubnet address: The original classful network portion plus a subnet field

Also known as extended network fieldSubnet and host field created from the original classful host portion

Subnet Mask helps identify the host/network part of an address

29IP Addressing

What a Subnet Mask Does

Tells the router the number of bits to look at when routingDefines the number of bits that are significantUsed as a measuring tool, not to hide anything

30IP Addressing

Possible Subnets and Hosts for a Class C Network

31IP Addressing

Possible Subnets and Hosts for a Class B Network

32IP Addressing

Possible Subnets and Hosts for a Class A Network

33IP Addressing

End System Subnet Mask Operation

34IP Addressing

Topology Example

A network topology using one IP network with six subnets

35IP Addressing

How Routers Use Subnet Masks

36IP Addressing

Working with subnets and masks: Analysis

Analysis of a given IP address/maskBinary/decimal maskSubnet number (network prefix)Next/previous subnetRange of addressesBroadcast addressThe first IP addressThe last IP addressImportant: are networks specified by 2 addresses overlapping?

IP Addressing 37

Working with subnets and masks: Design

Choosing a subnet mask to meet design requirements

Finding the only possible maskFinding multiple possible masksChoosing the mask that maximizes the number of subnets or hosts

IP Addressing 38

Subnet addresses

Reserved addresses:The smallest address (all “0”s) signifies the subnet number

128.12.17.144/28: x.y.z.1001000010.12.16.128/26: x.y.z.10000000

The last address (all “1”s) signifies the broadcast address

128.12.15.159/28: x.y.z.1001111110.12.16.191/26: x.y.z.10111111

IP Addressing 39

Subnetting: A useful reference chart

IP Addressing 40

Example: 199.214.17.132/28 (Class C)

IP@:x.y.z.10000100Borrowed bits: 4; Net bits: 28; Host bits: 4

Block size 16Mask(last byte only): 11110000; 240Subnet number: 199.214.17.128 (10000000)Next/previous subnets:

Next: 128 + 16= 144 (10010000)Previous: 128 – 16 = 112 (01110000)

Range of addresses: x.y.z.129 to x.y.z.143Broadcast address: 199.214.17.143First IP address: 199.214.17.129Last IP address: 199.214.17.142

IP Addressing 41

Example: 148.214.17.132/22 (Class B)

IP@:x.y.00010001.10000100Borrowed bits: 6; Net bits: 22; Host bits: 10

Block size: 4 (in the 3rd byte)Mask: “1”. “1”.11111100.00000000; 255.255.252.0Subnet number: 148.214.16.0 (0001000.00000000)Next/previous subnets:

Next: 16+4=20 (192.214.20.0)Previous: 16-4=12 (192.214.12.0)

Range of addresses: 192.214.16.1 to 192.214.19.255)Broadcast address: 199.214.19.255First IP address: 199.214.16.1Last IP address: 199.214.19.254

IP Addressing 42

Example: 9.214.17.132/12 (Class A)

IP@:Borrowed bits: __; Net bits: __; Host bits: __

Block size: __ (in the __ byte)Mask: Subnet number:Next/previous subnets:

Next:Previous:

Range of addresses:Broadcast address:First IP address:Last IP address:

IP Addressing 43

The Dread of Overlapping Subnets

In designing networks, care should be taken to prevent overlapping subnetsStep 1: calculate the subnet number and subnet broadcast address of each subnet.

Determines range of addresses within each subnet

Step 2: Compare the range of addresses in each subnet and look for any overlap

IP Addressing 44

The Dread of Overlapping Subnets

Is there any flaw in the following network?

IP Addressing 45

Problem Network

IP Addressing 46

172.16.4.2/23

172.16.5.2/24

172.16.2.1/23

1

2

3

The Dread of Overlapping Subnets

172.16.2.1/23Mask: 255.255.254.0 Subnet number: 172.16.2.0Broadcast @: 172.16.3.255

172.16.4.1/23Mask: 255.255.254.0Subnet number: 172.16.4.0Broadcast @: 172.16.5.255

172.16.5.1/24Mask: 255.255.255.0Subnet number: 172.16.5.0Broadcast @: 172.16.5.255

IP Addressing 47

Overlap!