CSEE W 4140 Networking Laboratory Lecture 3 IP

CSEE W 4140 Networking Laboratory Lecture 3: IP Forwarding and ICMP Jong Yul Kim 02. 04. 2009

IP in Internet Protocol Stack. Application Transport Network Link Physical

IP network 10. 0. 1. 11 128. 59. 16. 1

Two functions of network layer o Routing “Collective interactions of all routers to determine the paths that packets take on their trips from source to destination” o Forwarding “The transfer of a packet from an incoming link to an outgoing link within a single router. ”

Today’s topics

Subnet (RFC 950) o Hard to define… o General recipe “Detach each interface from its host or router, creating islands of isolated networks, with interfaces terminating the end points of the isolated networks. Each of these isolated networks is called a subnet. ”

Subnet Exercise 1

Subnet Exercise 2

Netmask o Hosts and routers within a subnet use netmask to determine whether the other host is directly connected or not

Classless Interdomain Routing (RFC 4632) o Examples n n n o 128. 59. 10 One host on CS net 128. 59. 16. 0/21 CS wired net 128. 59. 0. 0/16 Columbia wired net Two parts to an address n n prefix Network part (first 21 bits of CS wired) Host part (remaining 11 bits)

IPv 4 Datagram Format (RFC 791)

Router Architecture

Functional Components Control Datapath: per-packet processing

Forwarding Table Destination 10. 1. 0. 0/24 10. 1. 2. 0/24 10. 2. 1. 0/24 10. 3. 1. 0/24 20. 1. 0. 0/16 20. 2. 1. 0/28 Next Hop direct R 4 IP datagrams can be directly delivered (“direct”) or are sent to a router (“R 4”)

Delivery with forwarding tables to: 20. 2. 1. 2

Longest Prefix Matching Rule Destination Next Hop 11001000 11011111 200. 223. 0. 0/16 200. 16. 0. 0/13 11001000 00010 200. 22. 0. 0/15 11001000 0001011 o R 2 R 4 Direct Where would this packet go? Packet destination is: 200. 23. 146. 51 11001000 00010111 10010010 0011

ICMP (RFC 792) o Used to communicate network info n n o Error reporting Router advertisement and discovery Has type and code n n Type 8, code 0 = echo request Type 0, code 0 = echo reply o Replies have original sender’s IP header + 64 bits of data o Used by n n ping traceroute

IOS Command Mode Hierarchy Read the Introduction part 4 in textbook

Main Points of Lab 3 o Setting up static routes on: n n o Linux machines Cisco routers Routing packets using: n n n Proxy ARP ICMP Route Redirect Netmasks Kermit not used use picocom!

Homework o o o Prelab 3 due on Friday (02. 06. 2009) Lab report 2 due by beginning of lab 3 next week Read n RFC 2453 “RIP Version 2” parts 1 ~ 3

Announcements o In-class quiz next week n o Basic ARP, subnets, and IP forwarding Swipe Access n n Apar, Hai, Eric, Aaron, Abhinav Please check on Monday