cidr_cidr地址划分例题_vlsm cidr

CIDR - Classless Inter Domain Routing - was adopted to help ease the load imposed on internet and large network backbone routers by the increasing size of routing tables.

Large routing tables have several adverse effects:

Routers require more memory in order to store and manipulate their routing tables which increases operation costs.

Routing latency is increased due to the large amount of data contained in the routing tables.

Network bandwidth usage is increased by routing updates when routers exchange their routing tables.

A solution to these problems was found in CIDR. CIDR permits IP Address aggregation which in turn reduces the size of routing tables and so addresses the problems listed above.

So what is IP Address Aggregation? Quite simply, IP Address Aggregation means that several networks can be spanned by a single routing entry. Consider the following case:

Our router needs to route traffic for eight seperate networks through the same gateway (ip address 194.1.1.1):

ip route 66.100.50.0 255.255.255.224 194.1.1.1
ip route 66.100.50.32 255.255.255.224 194.1.1.1
ip route 66.100.50.64 255.255.255.224 194.1.1.1
ip route 66.100.50.96 255.255.255.224 194.1.1.1
ip route 66.100.50.128 255.255.255.224 194.1.1.1
ip route 66.100.50.160 255.255.255.224 194.1.1.1
ip route 66.100.50.192 255.255.255.224 194.1.1.1
ip route 66.100.50.224 255.255.255.224 194.1.1.1

Without CIDR, our routing table would need to maintain a seperate entry for each of the eight individual networks.

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