Information Technology Reference
In-Depth Information
default-metric
command is used to specify the seed metric that is used if one is not speci-
fied during redistribution The
default-metric
command has the following syntax for EIGRP:
default-metric
bandwidth delay reliability load mtu
Edge
Distribution
Campus
Network
Remote WAN
Sites
One-way
redistribution
Figure 11-21
One-Way Route Redistribution
OSPF Redistribution
This subsection reviews a few things you need to remember when designing a network
that will redistribute with OSPF.
When redistributing routes into OSPF, use the
subnets
keyword to permit subnetted
routes to be received. If you do not use it, only the major network route is redistributed,
without any subnetworks. In other words, OSPF performs automatic summarization to IP
classful network values. Also, unlike EIGRP and RIPv2, OSPF does not need a metric to
be specified during redistribution, neither does it need a seed metric to be specified be-
cause it uses a default metric for redistributed routes.
By default, redistributed routes are classified as external Type 2 (E2) in OSPF. You can use
the
metric-type
keyword to change the external route to an external Type 1 (E1). The net-
work design can take into account the after-redistribution cost (Type 2) or the after-redis-
tribution cost plus the path's cost (Type 1).
In Figure 11-22, Router B is configured to perform mutual redistribution between EIGRP
100 and OSPF process ID 50. In this example, you can use route maps and access lists to
prevent routing loops. The route maps permit or deny the networks that are listed in the
access lists. The
subnets
keyword redistributes every subnet in EIGRP into OSPF. This
book does not cover exact configurations.
Route Filtering
Filtering of routes can occur on either a redistribution point or in the routing domain to
prevent some parts of the network from accessing other sections of the network.
Filtering at a redistribution point provides the following:
Avoids routing loops
■
Avoids suboptimal routing
■
Prevents certain routes from entering the domain
■