Regarding source based outbound routing (with redundancy)

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1

Hello there!

I am trying to do a source based outbound routing between multiple
upstreams. Usually I picked outbound via localpref but here I wish to use
Provider 1 for say 10.10.10.0/24 while provider 2 for small chunk of it say
10.10.10.0/28. I wish to keep failover support and thus so if provider 2
fails, I wish to push traffic again via Provider 1.

Is this is possible only with VRF or I can push for some specific match
rule in route maps?

Thanks.

2

you really don't want to do policy routing :frowning:

3

you really don't want to do policy routing :frowning:

PBR has this tendency to be brittle in the face of topology changes.

There are much better way to outbound load-balance between providers offering same or similar quality routes to the same destination.

multi-AS multipath will do that if the peers are on the same router. BGPaddpath can do it for you if the peers are spread across routers.

joel

4

you really don't want to do policy routing :frowning:

PBR has this tendency to be brittle in the face of topology changes.

yup, exactly my point :frowning:

There are much better way to outbound load-balance between providers offering same or similar quality routes to the same destination.

multi-AS multipath will do that if the peers are on the same router. BGPaddpath
can do it for you if the peers are spread across routers.

these both will require seeing the longer prefix from the right peer
though, right? and selecting that would just be like natural selection
anyway...

yikes, I suppose you could:
  1) generate the longer prefix internally
  2) set it's next-hop to something reachable out both (all) peers
  3) metric the preferred peer's next-hop appropriately
  4) profit

but that sounds also kind of messy and prone to odd failures when
changes are made :frowning:
you'd be adding complexity that you'd have to track through the life
of your network :frowning: (and explain to anyone 'not you' working on the
network)

-chris

5

you really don't want to do policy routing :frowning:

PBR has this tendency to be brittle in the face of topology changes.

yup, exactly my point :frowning:

There are much better way to outbound load-balance between providers offering same or similar quality routes to the same destination.

multi-AS multipath will do that if the peers are on the same router. BGPaddpath
can do it for you if the peers are spread across routers.

these both will require seeing the longer prefix from the right peer
though, right? and selecting that would just be like natural selection
anyway…

so at this level if I can install two best paths in the fib then great I'll just hash flows between them… this does nothing for source based path selection but it does a lot for load-balancing between peers especially if there's substantial overlap of equidistant paths. If you have say 2914/3356 and you look at the amount of traffic that you can load-balance between them instead of simply tie-breaking on router-id or however far do your path algorythm you get, it's significant enough to matter.

yikes, I suppose you could:
1) generate the longer prefix internally
2) set it's next-hop to something reachable out both (all) peers
3) metric the preferred peer's next-hop appropriately
4) profit

but that sounds also kind of messy and prone to odd failures when
changes are made :frowning:

I go for the low hanging fruit, which is better usage of the information I already have.

6

I would need to lab it up, but assuming a MPLS core, can't you do a TE
tunnel from the source to the desired egress router?

7

Thanks for responses on this everyone.

I went ahead with VRF.