Default routes on BGP routers with full feeds

Adam Greene maillist at webjogger.net
Wed Nov 5 14:22:45 UTC 2014


We receive full routes and a default so we can perform traffic engineering within our network. We have links to multiple carriers, via multiple routers. We inject a default route into OSPF from distinct segments of our network, based on receiving the default route on that segment via eBGP. If the default route goes down, the default injected from another segment assumes priority and traffic routes out through that segment's carrier. It's easier to manage this kind of failover (for us) using default routes, so we don't have to carry full routes on all our core routers. We also prefer using a default route over engineering things based on some other arbitrary route learned from eBGP.

Thanks,
Adam

-----Original Message-----
From: NANOG [mailto:nanog-bounces+maillist=webjogger.net at nanog.org] On Behalf Of Marc Storck
Sent: Wednesday, November 05, 2014 6:53 AM
To: nanog at nanog.org
Subject: Re: Default routes on BGP routers with full feeds

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On Nov 5, 2014, at 7:49 AM, Andreas Larsen <andreas.larsen at ip-only.se> wrote:

There is one setup where you would need default route from your provider.

If you have no IBGP between two sites and your prefix is a large /16 on side and maybe a /18 from that /16 on another site. These site would not be able to talk to each other if you orginate from the same AS.

Other than that I see not harm in having both default and a full table since longest prefix match will always win even if you have 2 or more transits.

I think in that case you would use “allowas-in”.

Regards,

Marc
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