1. CSEE W4140 Networking Laboratory Lecture 3: IP Forwarding and ICMP Jong Yul Kim 02.04.2009

2. IP in Internet Protocol Stack Physical Link Network Transport Application

3. IP network 10.0.1.11128.59.16.1

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

5. Today’s topics

6. Subnet (RFC 950)  Hard to define…  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.”

7. Subnet Exercise 1

8. Subnet Exercise 2

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

11. Classless Interdomain Routing (RFC 4632)  Examples 128.59.19.10  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 Network part (first 21 bits of CS wired) Host part (remaining 11 bits) prefix

12. IPv4 Datagram Format (RFC 791)

13. Router Architecture

14. Functional Components Control Datapath: per-packet processing

15. Forwarding Table DestinationNext Hop 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 direct direct R4 direct R4 R4 IP datagrams can be directly delivered (“direct”) or are sent to a router (“R4”)

16. to: 20.2.1.2 Delivery with forwarding tables

17. Longest Prefix Matching Rule DestinationNext Hop 11001000 11011111R2 11001000 00010R4 11001000 0001011Direct  Where would this packet go? Packet destination is: 200.23.146.51 11001000 00010111 10010010 00110011 200.223.0.0/16 200.16.0.0/13 200.22.0.0/15

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

19. IOS Command Mode Hierarchy Read the Introduction part 4 in textbook

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

21. Homework  Prelab 3 due on Friday (02.06.2009)  Lab report 2 due by beginning of lab 3 next week  Read RFC 2453 “RIP Version 2” parts 1 ~ 3

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