[c-nsp] adjusting AD based on route tag/community?

[Rainer Clasen]

Hello,

rethinking some of our setups I'm currently wondering if there is a way
to adjust the administrative distance of routes learned through OSPF/BGP.

That'd help me in certain scenarios:
- mutual redistribution, prefering some routes on each redistribution
  point
- two level backups (i.e. if primary link and first backup fails, kick in
  the second one)
- initiating callback for a backup dialin on router A, while the client
  calls you on router B

The Idea is to have some special backup routes configured with a tag. This
tag is propagated through OSPF or BGP and used to set the AD on the other
routers. (OT: reading juniper docs I got the impression, you can play such
dirty tricks with the color)

I've also tried to abuse BGP weights for this, but had no luck. If you
redistribute routes into BGP, you have to set their AD > 200 to give BGP
the chance to override them. On the other hand you have to set the AD <
200 if you want a newly installed route to be considered for installation
if there is a BGP route active ...

Somehow I'd like to avoid using more-specific routes for the primary link
to overrule all backups ...

Rainer

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