
Customizing OSPF Services
117356-A Rev. A 7-17
Configuring the Metric Type for an ASE Advertisement
Each ASE that a boundary router injects into the AS includes a Type 1 or Type 2
metric. The Type 1 metric is equivalent to the metric of the non-OSPF route. The
Type 2 metric is either the metric of the non-OSPF route or the weight value
calculated for that route.
F
igure 7-2, for example, shows three routers in an OSPF domain. Router A and
router B are both configured to generate ASE routes using the route weight as the
Type 2 metric. Router A and router B both learn a route to destination X. The
following steps occur:
1. Boundary router A learns a route to destination X via EGP.
2. Boundary router A advertises the route to the internal router as an OSPF ASE
route. The Type 2 metric in the advertisement contains the route weight value
calculated for the EGP route to destination X.
3. Boundary router B learns a route to destination X via BGP.
4. Boundary router B advertises the route to the internal router as an OSPF ASE
route. The Type 2 metric in the advertisement contains the route weight value
calculated for a BGP route.
5. To determine the preferable route, the internal router compares the Type 2
metrics -- the EGP route weight and the BGP route weight.
6. The internal router chooses the BGP route -- the route with the lower weight.
Note: This parameter applies to boundary routers only.
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