Providers ISPs provide Internet connectivity ISPs are assigned a large chunk of

Providers isps provide internet connectivity isps are

This preview shows page 6 - 13 out of 23 pages.

Providers (ISPs) provide Internet connectivity ISPs are assigned a large chunk of contiguous network addresses Organizations contract with an ISP and are assigned one or more network address(es)
Image of page 6
Effect of Supernetting on Routing Problem: Recall: Routers (potentially) have an entry in their routing table for each unique network Assigning an organization 256 class C addresses might require 256 routing table entries Assigning an organization 1 class B address would require 1 routing table entry The information that Internet routers must store and exchange increases dramatically
Image of page 7
Effect of Supernetting on Routing (cont) Solution: Classless Inter-Domain Routing (CIDR) Collapse a block of contiguous network addresses into a single pair Example: (192.5.48.0, 3) specifies three network addresses: 192.5.48.0 192.5.49.0 192.5.50.0
Image of page 8
Effect of Supernetting on Routing (cont) Assume: a small number of ISPs each with a large block of addresses Example: four large ISPs: A: 195.0.0.0 – 195.63.255.0 (2 16 class C addresses) B: 195.64.0.0 – 195.127.255.0 (2 16 class C addresses) C: 195.128.0.0 – 195.191.255.0 (2 16 class C addresses) D: 195.192.0.0 – 195.255.255.0 (2 16 class C addresses)
Image of page 9
Effect of Supernetting on Routing (cont) A D C B Z Y X W V
Image of page 10
Effect of Supernetting on Routing (cont) Assume: customer X leases the addresses (195.17.0.0, 256) from ISP A ISP A’s routing table: A route to each of A’s subscribers: (195.17.0.0, 256) goes to X A route to each other ISP: (195.64.0.0, 2 16 ) goes to B (195.128.0.0, 2 16 ) goes to C (195.192.0.0, 2 16 ) goes to D Result: CIDR shortens routing tables
Image of page 11
CIDR Address Blocks and Bit Masks No need to restrict network numbers to class C addresses No need to use an integer to specify the block size
Image of page 12
Image of page 13

You've reached the end of your free preview.

Want to read all 23 pages?

  • Fall '14
  • IP address, Classless Inter-Domain Routing

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture