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Chapter 8

Hot Standby Routing Protocol (HSRP)

Request timed out.

C:\>

In this example, Host C's ARP time-out value is set to 6 minutes. After the
time expires, Host C will again be able to reach 14.4.4.4. However, Host C
has immediate access via Router A to any IP address it has not yet cached.

Advantages and Disadvantages of Proxy ARP

Proxy ARP offers a number of advantages and disadvantages. Among the
benefits are the following:

No need to configure clients with a gateway

Load balancing, although this is somewhat random

Immediate fault tolerance for addresses not recently contacted

There are also several drawbacks to Proxy ARP:

A lot of broadcast traffic

Must wait for ARP cache to time out in the event of failure

No control over which router is primary and secondary

Proxy ARP does provide some fault tolerance on a multi-access segment,

but it does not give the control administrators desire. A more robust and
flexible method is needed. In response to this need, Cisco developed the Hot
Standby Routing Protocol (HSRP).

Dynamic Routing Protocols

Another solution to the IP default gateway problem is to run dynamic rout-
ing protocols on all the hosts. The end-station host will then maintain a table
of which routers have a path to the remote network they need. Of course, all
your hosts on a network must be able to support dynamic routing. Both Unix
workstations and Windows NT workstations support IP RIP, for example.
However, the workstations will be slow to converge and have a tremendous
overhead of processing and memory.

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