NOTE:
Do not enable redistribution until you have used
restrict
to configure the redistribution filters. Otherwise, your network might become overloaded with routes
that you did not intend to redistribute.
Configuring ranges on an ABR to reduce advertising to
the backbone
Optional: Configuring ranges does the following to reduce inter-area advertising:
Summarizing routes
Enable a routing switch operating as an ABR to use a specific IP address and mask to summarize a range of
IP addresses into a single route advertisement for injection into the backbone. This results in only one
address being advertised to the network instead of all the addresses within that range. This reduces LSA
traffic and the resources needed to maintain routing tables.
Blocking routes
Prevent an ABR from advertising specific networks or subnets to the backbone area.
Each OSPF area supports up to 8 range configurations.
Influencing route choices by changing the administrative
distance default (optional)
The administrative distance value can be left in its default configuration setting unless a change is needed to
improve OSPF performance for a specific network configuration.
The switch can learn about networks from various protocols, including RIP and OSPF. Consequently, the routes to
a network may differ depending on the protocol from which the routes were learned. For the switches, the
administrative distance for OSPF routes is set at 110 for all route types (external, inter-area, and intra-area.)
The switch selects one route over another based on the source of the route information. To do so, the switch can
use the administrative distances assigned to the sources to influence route choices. You can change the distance
settings in the OSPF global context to enable preference of one route type over another.
Adjusting performance by changing the VLAN or subnet
interface settings
Optional: A setting described in this section can be configured with the same value across all subnets in a VLAN
or be configured on a per-interface basis with different values.
NOTE:
Most of the OSPF interface parameters also apply to virtual link configurations. However,
when used on a virtual link configuration, the OSPF context requirement is different and the
parameters are applied only to the interfaces included in the virtual link. See
on page 217.
Configuring OSPF interface authentication
Optional: OSPF supports two methods of authentication for each VLAN or subnet—simple password and MD5. In
addition, the value can be disabled, meaning no authentication is performed. Only one method of authentication
can be active on a VLAN or subnet at a time, and if one method is configured on an interface, configuring the
alternative method on the same interface automatically overwrites the first method used.
In the default configuration, OSPF authentication is disabled. All interfaces in the same network or subnet must
have the same authentication method (password or MD5 key chain) and credentials.
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