1. Addressing & Summarization

2. Overview
Poor addressing contributes to almost all large-scale network failure
Routing stability depends on
number of routes propagated
amount of work done each time network topology changes

3. Summarization
/ / / /24--> /22
Failure in /24 will be hidden from core
Only provide full topology information when needed

4. example

5. Networks to be summarized

6. Summarized network

7. Summarization from Dist. Layer to Core

8. Summarization from Dist. to Acess layer

9. Default route may thrash ARP cache
Router A caches all dest. IP ws1 ever tries and uses huge amount of memory
---> consumes ARP cache --> cache replacement --> thrashing

10. Example

11. Default route
Entire routing table on Router A is summarized into /0 (default)
Prevents access routers from participating in convergence
Suboptimal routing may result

12. Strategies for successful addressing
First come, first serve
Politically
Geographically
Topologically

13. First come, first serve Early days
Resulted in today’s Internet as a mess
Hard to summarize
Cause instability
Fig 2-10 Retana (8 routes are advertised into core)

14. Political addressing(by organization)
Assign a pool of addresses to each department
Small gain
Fig 2-11 Retana

15. Geographical addressing
Address space is divided geographically
May connect to different routers even if in the same region --> hard to summarize
Fig Retana

16. Topological addressing
Assign addresses based on the router to which network is attached
Easy summarization
Fig 2-13 Retana

17. Combine addressing schemes
Topological addressing: Hard to find department to which a network belongs
sol) combine topological addressing and political addressing
ex) 2nd octet: router, third octet: department