Telematics Chapter 6: Network Layer - Freie Universität Berlin

Classless Inter-Domain Routing (CIDR)
● Problem:
● Static categorization of IP addresses - how to use the very small class C
networks efficiently?
● Remedy: Classless Inter-Domain Routing (CIDR)
● Weakening of the rigid categorization by replacing the static classes by network
prefixes of variable length
● Form of an IP address: a.b.c.d/n
● The first n bits are the network identification
● The remaining (32 – n) bits are the host identification
● Example: 147.250.3/17
● The first 17 bits are network ID
and
the remaining 15 bits are host ID
10010011.11111010.00000011.00000000
Network ID Host ID
● Used together with routing: Backbone router, e.g., on transatlantic links only
considers the first n bits; thus small routing tables, little cost of routing decision
Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 6: Network Layer
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