1. Ch 22. Routing

2. 22.1 Direct and Indirect Delivery

3. 22.2 Forwarding Require a routing table – To find the route to the final destination Fast routing table lookup is the key to speed up forwarding process Reduce the size of routing table by keeping … – Only the next-hop info. (instead of the whole route) – Destination network info. (instead of each host info.) – Default router for un-specified destinations

4. Forwarding Process Forwarding module (for classless addressing)

5. Example Routing table of R1

6. Address Aggregation

7. Longest Mask Matching R1 R3

8. Others and Routing Table Entry More techniques to reduce routing table size – Hierarchical routing: try to use the hierarchy of the Internet – Geographical routing Common routing table entry

9. Application “netstat” “ifconfig” (“ipconfig” in Windows)

10. 22.3 Unicast Routing Protocols Autonomous system: – A group of networks and routers under a single admin.

11. Popular Routing Protocols – Intradomain protocol for routing within an AS – Interdomain protocol for routing between ASs

12. Distance Vector Routing Used for Routing Information Protocol (RIP) Each node (router) maintains a vector of minimum distance (cost) to every node Link cost

13. Building the Vector Initialization: build a vector from neighboring (direct connected) nodes Sharing: exchange the vector between neighboring nodes Updating: based on the received vectors, update the vector by recalculating the min. cost route Repeat “sharing & updating” periodically

14. Example Initialization Update at node A based on the vector received from node C

15. Loop Instability Count-to-infinity problem Solutions: defining infinity, split horizon, poison reverse

16. Link State Routing Used for Open Shortest Path First (OSPF) Each node has link information of ALL the link

17. Building Routing Tables Create the state of the links – Link State Packet (LSP) – Periodically, or when there is a change in topology Disseminate LSP to every router – flooding – If new LSP is received, copy it to other interfaces – If an old LSP is received, discard it Each node will collect LSPs from all nodes Find the shortest path tree – Dijkstra algorithm

18. Dijkstra Algorithm Example of node A

19. Path Vector Routing “Interdomain routing” used for Border Gateway Protocol (BGP) In general, similar to distance vector routing Main differences – Speaker node: a node that acts on behalf of the AS – Loop prevention: routing tables show entire path

20. Homework Exercise – 16 – 23 – 24 – Assume that the cost is the hop-distance, i.e., each link cost = 1, and that the router of RIP routing table and the router C is directly connected (i.e., their distance is 1-hop).

21. Additional problem – Link state routing is operating with topology shown below – Assume that A is chosen as a root – Find the shortest path tree using Dijkstra algorithm (draw all the steps as in Fig. 22.23) 7 1 2