Fault-Tolerant Routing
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Fault-Tolerant Routing
T
he problem with IP routing is the default gateway configuration on
a workstation. When a host is configured with a default gateway, it will
always use that address to send packets out of the local network. If the router
that is assigned to the default gateway goes down, the host is down to the
outside world until the default gateway is fixed.
There are a few solutions, one being HSRP, of course. However, let's take
a look at the other options:
Proxy ARP
Enabling dynamic routing protocols on the hosts
IRDP
HSRP
Proxy ARP
Proxy Address Resolution Protocol (Proxy ARP) is a variation of the ARP
protocol in which an intermediate device, such as a router, sends an ARP
response on behalf of an end node to the requesting host. Proxy ARP has
been defined and referenced in many RFCs.
This technology once had a strong following, and one benefit is that it can
lessen bandwidth use on slow-speed WAN links. As networks grew, how-
ever, Proxy ARP did not scale with them.
In this section, you will learn about the origin, implementation, and
advantages and disadvantages of Proxy ARP.
The Origin of Proxy ARP
Originally, Proxy ARP was designed for dial-up connections, such as the
example shown in Figure 8.1. You could give the dial-in machine an address
taken from the subnet of the local LAN without having to create a new sub-
net. This conserved a substantial amount of address space.
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