[c-nsp] IOS-XR OSPF path selection

Robert Blayzor rblayzor.bulk at inoc.net
Thu Feb 28 13:16:38 EST 2013

According to the IOS-XR documentation on OSPF:

ASBR routes can be advertised as a Type 1 or Type 2 ASE. The difference between Type 1 and Type 2 is how the cost is calculated. For a Type 2 ASE, only the external cost (metric) is considered when multiple paths to the same destination are compared. For a Type 1 ASE, the combination of the external cost and cost to reach the ASBR is used. Type 2 external cost is the default and is always more costly than an OSPF route and used only if no OSPF route exists.

This seems to not be the standard behavior of IOS or NX-OS.  With IOS or NX-OS you can influence type-1 or type-2 routes via interface cost.  But in IOS-XR only type-1 are effected by interface cost, but not type-2.

If is an issue when trying to control path selection manually on a local router.  Is there a way to change this behavior in IOS-XR so that type-2 route path selection is effected by configured or calculated interface cost?

Robert Blayzor
rblayzor at inoc.net

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