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This section reviews the
material just presented. The following section presents a scenario
in which an improper use of static routes and gateways of last
resort can cause connectivity failures. The main figure shows the
network diagram that will be used for this scenario.
Two types of IP
network addresses are under considered in this section:
- Nonlocal
domain addresses
(a
major network address that the router does not have a physical
connection to) --- In the main figure, router B does not have an
explicit route to 168.72.5.0. However, it does have a gateway of
last resort of 10.0.0.0. This gateway of last resort is created
with a static route to 10.0.0.0 that points at 168.71.6.1 and
configures the ip default-network 10.0.0.0 command.
This route is sufficient for router B to forward packets to
167.72.5.0 because router B has no local context for 168.72.0.0
(it is not a local domain).
Local domain
addresses (a
major network address that the router does have a physical
connection to) ---
Router A must have either an explicit route back to
168.71.8.0 or a static route pointing to 168.71.8.0 with a next hop
of 168.71.6.3. A gateway of last resort will not allow router A to
reach 168.71.8.0 because router A is connected to the major net
168.71.0.0. This connection makes 168.71.8.0 part of the router A
local domain. Routers expect to have explicit routes for all subnets
in their local domains. It is possible to get around this by
installing a static route to the major network alone. However, this
can lead to problems when configured improperly.
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