TCP IP Illustrated

Cidr also uses a technique whereby the best match is

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Unformatted text preview: arization within the European routers using additional bits beyond the 7 high-order bits of the 32-bit mask. CIDR also uses a technique whereby the best match is always the one with the longest match: the one with the greatest number of one bits in the 32-bit mask. Continuing the example from the previous paragraph, perhaps one service provider in Europe needs to use a different entry point router than the rest of Europe. If that provider has been allocated the block of addresses 194.0.16.0 through 194.0.31.255 (16 class C network IDs), routing table file:///D|/Documents%20and%20Settings/bigini/Docu.../homenet2run/tcpip/tcp-ip-illustrated/dynamic.htm (15 of 17) [12/09/2001 14.46.53] Chapter 10. Dynamic Routing Protocols entries for just those networks would have an IP address of 194.0.16.0 and a mask of 255.255.240.0 (0xfffff000). A datagram being routed to the address 194.0.22.1 would match both this routing table entry and the one for the rest of the European class C networks. But since the mask 255.255.240 is "longer" than the mask 254.0.0.0, the routing table entry with the longer mask is used. The term "classless" is because routing decisions are now made based on masking operations of the entire 32-bit IP address. Whether the IP address is class A, B, or C makes no difference. The initial deployment of CIDR is proposed for new class C addresses. Making just this change will slow down the growth of the Internet routing tables, but does nothing for all the existing routes. This is the short-term solution. As a long-term solution, if CIDR were applied to all IP addresses, and if existing IP addresses were reallocated (and all existing hosts renumbered!) according to continental boundaries and service providers, [Ford, Rekhter, and Braun 1993] claim that the current routing table consisting of 10,000 network entries could be reduced to 200 entries. 10.9 Summary There are two basic types of routing protocols: interior gateway protocols (IGPs), for routers within an au...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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