Class Notes (1,100,000)
US (480,000)
UCSD (8,000)
CSE 123 (20)
Lecture 11

CSE 123 Lecture Notes - Lecture 11: Address Space, Ipv6 Address, Network Address Translation

Computer Science and Engineering
Course Code
CSE 123
Alex Snoeren

This preview shows half of the first page. to view the full 3 pages of the document.
IP Address Problem (1991)
- Address space depletion
- Class C too small for most orgs!
CIDR (Classless Inter-Domain Routing) - 1993
- does NOT create any more addresses! (still 32-bit addresses)
- no longer “constrained” to Class A-C addresses!
- networks described by variable-length prefix & length
- allows “arbitrary” allocation between network and host address
| Network | Host
Prefix Mask = # sig bits representing prefix
E.g. contained within
- is network and remainder (95.1.2) is host
Pro: Finer-grained allocation; aggregation
Con: More expensive lookup: longest prefix match
- only use the longest name in your forwarding table
- can you have 2 network names of the SAME length? NO
- if they’re the same length, same pattern, then they can’t be different! (No ties)
Longest Matching Prefix
- forwarding table contains many prefix/length tuples
- start from the MSBs, ALL the way to the prefix
E.g. and
0001 | 0000
0001 001 | 0 ← longest matching prefix! (23 bits)
Not a simple table! Requires multiple memory lookups
Route Aggregation - if they get a bunch of networks in the same direction, and all “contiguous”
in the sorted list of names, can be sorted in a more efficient way
- combine adjacent networks in forwarding tables!
0001 000 | 0 //
0001 001 | 0 //
0001 010 | 0 //
- send me ANYTHING w/ addresses beginning
Most Specific Route - but what if address range is NOT contiguous?
- Send me anything with address beginning or (special and more
- Move in large blocks, not small ones!
- is there a “default” router which matches everything? YES! (# / 0)
You're Reading a Preview

Unlock to view full version