Networks, TCP/IP, and Network-Based attacks Networks, TCP/IP, and Network-Based attacks

Lesson 2

ReviewIs an ROI from Security Possible?

ReviewIs an ROI from Security Possible?

Security as an ROI

Improved Security ROI

Security that provides savings in the budget

Security that provides additional revenue

Computer System BasicsComputer System Basics

Operating SystemsManage the computer’s resources– Memory management– Scheduling– Access Controls

Lots of different operating systems– Win9X, Win2K, WinME, NT, Unix, Linux, VMS

NetworksNetworks

What is a network?Two or more systems connected togetherLAN (local area network)WAN (Wide area network)MAN (metropolitan area network)

Network TopologiesNetwork Topologies Topology – the physical arrangement of the network.

Completely ConnectedStarRingBus

Characteristics# of connections# of “hops”Addition of new nodesFairnessCollisions and points of failure

Network TopologiesNetwork Topologies

?

Network Topologies -- StarNetwork Topologies -- Star

Adv: distance = 2 hops connections = n-1

DisAdv: 1 point of failure

Fairness? Addition of new nodes? Congestion(collisions)?

Network Topologies -- RingNetwork Topologies -- Ring

Adv: avg dist = (n-1)/2 hops connections = n

DisAdv: many points of failure

Fairness (token)? Addition of new nodes? Congestion(collisions)?

Network Topology -- BusNetwork Topology -- Bus

Adv: distance = 1 hop connections = n

DisAdv: Collisions

Fairness? Addition of new nodes?

ProtocolsProtocols

A protocol is an agreed upon format for exchanging information.

A protocol will define a number of parameters:Type of error checkingData compression methodMechanisms to signal reception of a transmission

There are a number of protocols that have been established in the networking world.

OSI Reference ModelOSI Reference Model ISO standard describing 7 layers of protocols

Application: Program-level communicationPresentation: Data conversion functions, data format, data encryptionSession: Coordinates communication between endpoints. Session state maintained for security.Transport: end-to-end transmission, controls flow of dataNetwork: routes data from one system to the nextData Link: Handles physical passing of data between nodesPhysical: Manages the transmission media/HW connections

Abstraction is the principle, you only have to communicate with the layer directly above and below

TCP/IP Protocol SuiteTCP/IP Protocol Suite TCP/IP refers to two network protocols used on the

Internet:Transmission Control Protocol (TCP)Internet Protocol (IP)

TCP and IP are only two of a large group of protocols that make up the entire “suite”

A “real-world” application of the layered concept. There is not a one-to-one relationship between the

layers in the TCP/IP suite and the OSI Model.

OSI and TCP/IP comparisonOSI and TCP/IP comparisonOSI Model

Application

Presentation

Session

Transport

Network

Data-link

Physical

TCP/IP Protocol Suite

NFSFTP, Telnet,SSH, SMTP SMBHTTP, NNTP

RPC

TCP,UDP

IP ICMPARP

Physical

Application-levelprotocols

Network-levelprotocols

TCP/IP Protocol SuiteTCP/IP Protocol SuiteUser

ProcessUser

ProcessUser

ProcessUser

Process

TCP UDP

IP

HWInterface

RARPARP

ICMP IGMP

Media

Encapsulation of dataEncapsulation of dataUser Data

User DataAppl

header

Application dataTCP

header

Application dataTCP

headerIP

header

Application dataTCP

headerIP

headerEthernetheader

Ethernettrailer

Ethernet Frame

IP Datagram

TCP segment

application

TCP

IP

Ethernetdriver

Ethernet

Demultiplexing of a received Ethernet FrameDemultiplexing of a received Ethernet Frame

application application application application

UDPTCP

ICMP IGMP

IP

ARP RARP

Ethernetdriver

Incoming Frame

IP DatagramIP Datagram

32 Bits

Source Address

Destination Address

Time-to-live Protocol Header Checksum

Version head lngth Type of Service Total Length

Identification Flags Frag Offset

Options (if any)

Data

TCP Packet StructureTCP Packet Structure32 Bits

Source Port Destination Port

Sequence Number

Acknowledgment Number

Options (if any)

Data

WindowData Offset Reserved Flags

Checksum Urgent Pointer

TCP establishes a “virtual circuit” between client and server.

Establishment of a TCP connection(“3-way Handshake”)

Establishment of a TCP connection(“3-way Handshake”)

client ServerSYN

Client sends connection request,Specifying a port to connect toOn the server.

client ServerSYN/ACK

Server responds with both anacknowledgement and a queuefor the connection.

client ServerACK

Client returns an acknowledgementand the circuit is opened.

User Datagram Protocol (UDP)User Datagram Protocol (UDP)

UDP is a connectionless transport layer protocol that provides no reliability and has no mechanism for connection establishment or termination.

UDP makes no guarantee about packet delivery. This “fire and forget” naturemeans a packet is placed on the network and you just hope it gets to where itwas supposed to go to.

UDP is commonly used for network services that are not sensitive to anoccasional lost (dropped) packet.

Because of the relative overall reliability of the network, it has become lessimportant to have a guaranteed service and thus UDP is a good choice for manystreaming services.

Application ProtocolsApplication Protocols

HTTP – HyperText Transfer Protocol FTP – File Transfer Protocol Telnet – A terminal communications facility SMTP – Simple Mail Transfer Protocol SSH – Secure SHell

Common PortsCommon Ports Common Ports used to facilitate communication

between common protocolsHTTP: TCP port 80Telnet: TCP port 23FTP: TCP port 20 and 21SMTP: TCP port 25SSH: TCP port 22DNS: UDP and TCP port 53

RoutingRouting

The overall process of delivering a packet from point A to point B. It is the job of the router to know where to send a packet in order to reach its

destination Routing tables are used to determine where to send a packet.

Static: entries entered once and not updatedRouting Information Protocol (RIP): entire tables shared on a periodic basis. Not very efficient or secure.Open Shortest Path First (OSPF): Table maintained to determine what the shortest path is to specific destinations. Tremendous overhead.Border Gateway Protocol (BGP): Peer routers (neighbors) exchange routing information. Entire table initially loaded but subsequent changes limited to updates.

IP AddressingIP Addressing We’re all familiar with the concept of URL’s and IP addresses, we’ve been using them

for a while. We normally like to recall the URL, not the IP address but the network requires the address, DNS (Domain Name Service) solves this problem for us.

When you use a site’s name, your computer will send a DNS query to your local DNS server, if it knows the address it will return it otherwise it will send a query to a higher-level domain server, which may forward the query further up and so forth until the address is obtained.

There are two basic ways to assign an IP address to a computer:Static – a specific address is assigned to a specific system and stays with itDHCP (Dynamic Host Configuration Protocol) – a dynamic addressing scheme that allows us to allocate IP addresses on a first-come, first-served basis. When a device connects to the network, it queries a DHCP server to obtain an IP address from a range of addresses. If the server runs out of addresses, the requestor is out of luck.

– Method allows for more people to access the network without using as many addresses

Network Address Translation (NAT)Network Address Translation (NAT)

There are a limited number of IP addresses available and not every system needs one.

NAT was developed to provide a means to translate private IP addresses into public IP addresses.

A device (typically a router or firewall) will accomplish this translation process.Source: 10.1.1.123Destination: 207.25.71.23

Source: 63.69.110.110Destination: 207.25.71.23

Source: 207.25.71.23 Destination: 10.1.1.123

Source: 207.25.71.23 Destination: 63.69.110.110

Firewall performs NAT

Network Address TranslationNetwork Address Translation

A modern NAT gateway must change the Source address on every outgoing packet to be its single public address. It therefore also renumbers the Source Ports to be unique, so that it can keep track of each client connection. The NAT gateway uses a port mapping table to remember how it renumbered the ports for each client's outgoing packets. The port mapping table relates the client's real local IP address and source port plus its translated source port number to a destination address and port. The NAT gateway can therefore reverse the process for returning packets and route them back to the correct clients.

When any remote server responds to an NAT client, incoming packets arriving at the NAT gateway will all have the same Destination address, but the destination port number will be the unique Source Port number that was assigned by the NAT. The NAT gateway looks in its port mapping table to determine which "real“client address and port number a packet is destined for, and replaces these numbers before passing the packet on to the local client.

Internet Control Message Protocol (ICMP)Internet Control Message Protocol (ICMP)

ICMP uses the IP datagram delivery facility to send its messages.

IP Header ICMP message 20 bytes

(contents -- depends on type and code)

8-bit type 8-bit code 16-bit checksum

The format for the ICMP message is as follows:

ICMP performs the following control, error reporting, and informationalFunctions for TCP/IP:

- Flow Control- Detecting unreachable destinations- Redirecting routes- Checking remote hosts (e.g. ping)

Internet Control Message Protocol (ICMP)Internet Control Message Protocol (ICMP)

Type Code Message0 0 Echo Reply3 0 Net Unreachable3 1 Host Unreachable3 3 Port Unreachable5 1 Host Redirect8 0 Echo Request11 0 Time-to-live exceeded13 0 Timestamp Request14 0 Timestamp Reply

Typical Net-based Attacks -- WebTypical Net-based Attacks -- Web

“Popular” and receives a great deal of media attention.

Attempt to exploit vulnerabilities in order to:Access sensitive data (e.g. credit card #’s)Deface the web pageDisrupt, delay, or crash the serverRedirect users to a different site

Typical Net-based attacks -- SniffingTypical Net-based attacks -- Sniffing Essentially eavesdropping on the network Takes advantage of the shared nature of the

transmission media. Passive in nature (i.e. just listening, not broadcasting) The increased use of switching has made sniffing more

difficult (less productive) but has not eliminated it (e.g. DNS poisoning will allow you to convince target hosts to send traffic to us intended for other systems)

Typical Net-Based Attacks –Spoofing, Hijacking, Replay

Typical Net-Based Attacks –Spoofing, Hijacking, Replay

Spoofing attacks involve the attacker pretending to be someone else.

Hijacking involves the assumption of another systems role in a “conversation” already taking place.

Replay occurs when the attacker retransmits a series of packets previously sent to a target host.

Typical Net-Based Attacks –Denial of Service

Typical Net-Based Attacks –Denial of Service DOS and Distributed DOS (DDOS) attacks have

received much attention in the media in the last year due to some high-profile attacks.

Several varieties:Flooding – sending more data than the target can processCrashing – sending data, often malformed, designed to disable the system or serviceDistributed – using multiple hosts in a coordinated attack effort against a target system.

IPv4 versus IPv6IPv4 versus IPv6 From the IPv6 FAQ, what are the merits of IPv6?

scalability:IPv6 uses 128bit address space. Address length is 4 times longer than IPv4. security:IPv6 basic specification includes security. It includes packet encryption (ESP:Encapsulated Security Payload) and source authentication (AH:Authentication Header). [confidentiality and authentication]real-time:To support real-time traffic such as video conference, IPv6 has "Flow Label". Using flow label, routers can know which end-to-end flow a packet belongs to, and then find out the packet which belongs to real-time traffic. [needed to allow for prioritization of traffic]autoconfiguration:IPv6 basic specification includes address autoconfiguration. So, even a novice user can connect their machine to network. specification optimization:IPv6 keeps good parts and discards old and useless parts of IPv4.

IP Security (IPSEC)IP Security (IPSEC) Optional in IPv4, supported in IPv6. Two major modes:

Tunnel: encrypts both the data and header portions of the packet.Transport: encrypts the data portion of the packet.

Requires both ends to be using IPSEC (obviously, since one end will encrypt, the other needs to be able to decrypt).

About IPSEC (from the IPSEC FAQ) About IPSEC (from the IPSEC FAQ)

IPsec = AH + ESP + IPcomp + IKEIPsec consists of a couple of separate protocols, listed below:

– Authentication Header (AH): provides authenticity guarantee for packets, by attaching strong crypto checksum to packets. If you receive a packet with AH and the checksum operation was successful, you can be sure about two things :

The packet was originated by the expected peer. The packet was not generated by an impersonator. The packet was not modified in transit.

– Encapsulating Security Payload (ESP): provides confidentiality guarantee for packets, by encrypting packets with encryption algorithms. If you receive a packet with ESP and successfully decrypted it, you can be sure that the packet was not wiretapped in the middle.

– IP payload compression (IPcomp): ESP provides encryption service to the packets. However, encryption tends to negatively impact compression on the wire. IPcomp provides a way to compress packets before encryption by ESP (Of course, you can use IPcomp alone if you wish to).

– Internet Key Exchange (IKE): AH and ESP need shared secret keys between peers. For communication between distant locations, we need to provide ways to negotiate keys in secrecy. IKE will make this possible.

EthernetEthernet The most common physical layer protocol. A shared media protocol, collisions possible

Uses CSMA/CD to control traffic Several different variations of Ethernet exist

10Base-2 : Thinnet (thin coax)10Base-5: Thicknet (earliest version, thick coax)10Base-T: Standard twisted pair Ethernet100Base-T: Fast Ethernet1000Base-T: Gigabit Ethernet

SummarySummary

What is the Importance and Significance of this material?

How does this topic fit into the subject of “Voice and Data Security”?