Default Route Configuration Example - Zte ZXR10 5900E Series User Manual

ZXR10 5900E Series User Manual (IPv4 Volume)

Default Route Configuration Example

A router might not be able to determine the routes to all other
networks. To provide complete routing capability, the common
practice is to use some routers as smart routers and give the re-
maining routers default routes to the smart router. (Smart routers
have routing table information for the entire internet work.) These
default routes can be passed along dynamically and can be con-
figured into individual routers.
Most dynamic interior routing protocols include a mechanism for
causing a smart router to generate dynamic default information
that is then passed along to other routers.
If a router cannot route a packet, the packet has to be dropped.
However, it is not hoped that the packet is dropped in an "un-
known" destination. To support complete connection of the router,
it should have a route connected to a network. If the router wants
to keep complete connection and meanwhile does not need to
record each independent route, the default route can be used. By
use of the default route, an independent route can be designated
to indicate all the other routes.
An example is given in the following to describe the functions and
use of the default route.
F 3 DEFAULT ROUTE CONFIGURATION
IGURE
As shown in Figure 3. R2 is connected to router R3 in the Inter-
net. R2 does not record the addresses of all the networks on the
Internet. It uses a default route to directly send unknown packets
to R3 for proper processing. The configuration of the default route
in R2 is as follows:
ZXR10_R2(config)#ip route 0.0.0.0 0.0.0.0 211.211.211.2
When the default route is used in routing protocol configuration,
the default route varies with the routing protocols.
If the default route is configured for a router where an RIP runs,
the RIP will advertise the default route 0.0.0.0/0 to its neighbor,
and even route redistribution is not needed in the RIP domain.
For the OSPF protocol, a router where the OSPF protocol runs will
not inject the default route into its neighbor automatically. For the
OSPF to send the default route to the OSPF domain command no-
tifies default route must be used. If it is necessary to redistribute
the default route in the OSPF domain, such an advertisement is
normally implemented by an ASBR (Autonomous System Border
Router) in the OSPF domain.
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