ITP 457 Network Security Networking Technologies II UDP

ITP 457 Network Security Networking Technologies II UDP, IP, and NAT

Overview l l l UDP IP NAT

UDP l l l UDP – User Datagram Protocol Also member of TCP/IP TCP and UDP are cousins An application developer can choose to transmit data using either TCP or UDP Both protocols cannot be used simultaneously in an application

UDP Characteristics l l Connectionless – the protocol doesn’t know or remember the state of a connection Does not have concept of l l l Session initiation Acknowledgement No error checking – does not retransmit lost packets nor does it put them in proper order

UDP l l l UDP also called: “Unreliable Damn Protocol” It is inherently unreliable Unreliability is ok – IF it can buy you SPEED! Some applications more interested in getting packets across the network and don’t need super high reliability. Good protocol for a large number of connections

UDP l Services that use UDP are l l l l Streaming Video/ Audio DNS queries Online Games Voice-over-IP (Vo. IP) DHCP DNS SNMP RIP

UDP header UDP source port UDP destination port Message Length Checksum Data

UDP Ports l l l UDP – 65, 535 ports Some typical ports: l 53 – DNS (Domain Name Server) l 67 – DHCP (Dynamic Host Control Protocol) l 69 – TFTP (Trivial File Transfer Protocol) l 161 – SNMP (Simple Network Management Protocol) l 514 – Syslog l 6112 – Battle. NET l 14567 – Battlefield 1492 l 26000 – Quake Server l 27015 – Halflife Server For a searchable database of known ports: l http: //www. ports-services. com/

IS UDP less secure than TCP? l l YES! Absence of three-way handshake implies no Sequence numbers or no control bits. Difficult for firewalls and routers to track where the ends systems are in their communications We cannot completely turn off UDP, due to some of the necessary protocols that use UDP

Internet Protocol( IP) l l l IP handles end-to-end delivery Most commonly used network layer protocol All traffic on the internet uses IP

Internet Protocol ( IP) l l Upon receiving packet from Transport layer, IP layer generates a header Header includes : source and destination IP addresses Header is added to front of TCP packet to create a resulting IP packet. Purpose of IP is to carry packets end to end across a network.

IP header Source IP address Destination IP address Data

IP addresses l l Identify each individual machine on the internet 32 bits in length Hackers attempt to determine all IP address in use on a target network – “network mapping” Hackers generate bogus packets appearing to come from a given IP address – “IP address spoofing”

IP Addresses in depth l 32 bits, with 8 bit groupings l l l E. x: 192. 168. 0. 1 Each number between the dots can be between 0 and 255 4 billion combinations l l Not really Allocated in groups called address blocks § § 3 sizes, based on the class of the address Class A, Class B, and Class C

Class A Addresses l l l l Giant organizations There are no more available All IP addresses are of the form: 0 – 126. x. x. x x can be between 0 and 255 The first octet is assigned to the owner, with the rest being freely distributable to the nodes Has a 24 bit address space Uses up to half of the total IP addresses available!!! Who owns these? ? ? l Internet Service Providers l Large internet companies l Google, CNN, WB

Class B Addresses l l l Large Campuses or Organizations l Example: Colleges, including USC These are running out!!! All Class B Addresses are of the form: 128 - 191. x. x. x Where x can take any number between 0 and 255 The first two octets are assigned to the address block owner, with the last two being freely distributable l Example: 128. 125. x. x USC l Example: 169. 232. x. x UCLA 16 -bit address space ¼ of all IP addresses belong to Class B Addresses

Class C Addresses l l Small to mid-sized businesses A fair number left All Class C Addresses have the following format: 192 -232. x. x. x The first three octets are assigned, with the last being freely distributable l Only 253 distributable addresses within a Class C Address

Reserved Addresses l Private Networks (no public connections) l l l 10. x. x. x 172. 16. x. x 192. 168. x. x 127. x. x. x – local network (loopback) 255 – broadcast – sends to everyone on the network

Netmasks l IP address has 2 components l l Network address Host address Determined by the address and the class of the address Example (Class C): l l l IP Address: 192. 168. 3. 16 Network address: 192. 168. 3 Host address: 16

Packet Fragmentation l l Various transmission media have different characteristics Some require short packets others require longer packets E. g. satellite – longer packets Local LAN – shorter packets

Packet Fragmentation l l l To optimize packet lengths for various communication links, IP offers network elements (routers and firewalls) the ability to slice up packets into smaller pieces, a process called fragmentation. The end system’s IP layer is responsible for reassembling all fragments Hackers use packet fragmentation to avoid being detected by Intrusion Detection Systems

Lack of Security in IP l l l IP version 4 does not include any security All components of packets are in clear text, nothing is encrypted Anything in the header or data segment can be viewed or modified by the hacker l l TCP/UDP Hijacking “Man-in-the-middle” attack

ICMP l l l ICMP – Internet Control Message Protocol It is the Network Plumber Its job is to transmit command control information between networks and systems

ICMP examples l l “ping” request = ICMP Echo message If the “pinged” system is alive it will respond with ICMP Echo Reply Message l l l Try pinging l www. google. com l www. yahoo. com l www. cnn. com Will they all work? Some sites have disabled ping. Why? l l Ping-of-death a ping too big Ping flooding type of denial-of-service attack

Routers and packets l Routers l l l Transfer packets from network to network They determine the path that a packet should take across the network specifying from hop to hop which network segments the packets should bounce through as they travel across the network Most networks use dynamic routing l l RIP, EIGRP We will be discussing these technologies later in the course

Network address translation l l NAT Blocks of addresses are allotted to ISP’s and organizations l l Classes of IP Addresses What happens when we have more computers than IP Addresses? l l l We have a Class C address – allows 253 computers Our organization has 1000 computers What do we do? ? ?

Solution? l Reserve a range of IP addresses to build your own IP network l l 10. x. y. z - un-routable IP addresses 172. 16. y. z 192. 168. y. z How to connect these machines to Internet?

Network Address Translation l Use a gateway /router to map invalid addresses to valid IP addresses l l Translates your local address to a routable address Router receives one IP Address l Either dynamically assigns addresses to all the nodes behind the router, or it is assigned statically using nonroutable addresses § l If dynamic, uses DHCP (Dynamic Host Configuration Protocol) When someone inside the network wants to access a computer outside the local network (the internet), the request is sent to the router, which uses NAT to send the request to the internet

NAT and security? l Does NAT improve security? l l It hides internal IP addresses from hacker NAT must be combined with “firewalls” for optimum security

Firewalls

Firewalls l l Network traffic cops Tools that control the flow of traffic going between networks By looking at addresses associated with traffic, firewalls determine whether connections should be transmitted or dropped We will cover the setup and configuration of firewalls in great depth later in class