IPv6 Configuration Guide K/KA/KB.15.15

5. Optional: Change the administrative distance setting.
NOTE: In the default configuration, redistribution is permitted for all routes from supported
sources.
Enable redistribution after you have configured route-maps defining the route policies you
want to apply to route redistribution in the OSPFv3 domain. Otherwise, your AS may become
overloaded with routes that you did not intend to redistribute.
About configuring ranges on an ABR to reduce advertising to the backbone
Configuring ranges does the following to reduce inter-area advertising:
Summarizing routes
Enables a routing switch operating as an ABR to use a specific prefix to
summarize a range of IPv6 addresses into a single RA 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
Prevents an ABR from advertising specific networks or subnets to the backbone
area.
Each OSPFv3 area supports up to eight range configurations.
About influencing route choices by changing the administrative distance
default (optional)
The administrative distance value can be left in its default configuration setting (110) unless a
change is needed to improve OSPFv3 performance for a specific network configuration.
The switch can learn about networks from various protocols. Consequently, the routes to a network
may differ depending on the protocol from which the routes were learned. On the routing switches,
the administrative distance for OSPFv3 routes is set at 110 for all route types (external, inter-area,
and intra-area).
The routing switch selects routes on the basis of route source information. To enable this operation,
the administrative distance assigned to each source is used to influence route choices. You can
change the distance settings in the OSPFv3 global context to enable preference of one route type
over another.
About enforcing strict LSA operation for graceful restart helper mode
(optional)
OSPFv3 operation on the routing switches includes helper mode operation for graceful restart of
OSPFv3 on a neighboring router upon receipt of a "grace LSA" from the neighbor. In the default
configuration, helper mode operation in this case includes terminating graceful restart support
("strict LSA" operation) on the routing switch if it detects a topology change requiring updated
LSAs during the restart period of the neighboring router. Terminating this support forces the helper
routing switch to re-establish its LSAs and OSPFv3 functions on the network segment affected by
the OSPFv3 restart on the neighboring router. (For more information on OSPFv3 graceful restart,
see RFC 3623.)
In the default OSPFv3 configuration, the default helper mode operation terminates graceful restart
if topology changes affect the network segment.
About configuring ranges on an ABR to reduce advertising to the backbone 259