announcing BGP prefixes from the same AS at different sites?
raph at futomaki.net
Wed Sep 10 18:45:28 CEST 2014
Back to basics :
1) Your IGP should be use to propagate loopback (and interco if needed)
of your router. You may use multiple path between your router for
2) Your IBGP should be a full mesh of your loopback core router using
BGP (unless using RR). A IBGP session should not failed, if so you are
loosing your route associated to the router. The redundancy is done by
the IGP (if you have multiple path)
I agreed that disabling as-path loop is an hacky workarroud, which may
not work, and make thing unclear. Bad idea for me.
So two options :
- make some tunnel, and establish an IGP/IBGP session with it.
- or use statics routes (with tracking optionnaly).
Le 10/09/2014 15:38, Thomas Johnson a écrit :
> Thank you for the feedback. I was aware of disabling aspath loop
> detection, but have not yet explored it; based on my reading, it seemed
> like a hacky workaround. Are there any drawbacks to this approach, aside
> from the obvious possibility of creating loops?
> With regard to an IBGP mesh, it seems that if a BGP session in my mesh
> fails, routing of prefixes between the affected routers fails. Is this
> the expected behavior? Is this where I should be using an IGP to route
> around the failed IBGP?
> On Mon, Sep 1, 2014 at 11:54 AM, Raphael Mazelier <raph at futomaki.net
> <mailto:raph at futomaki.net>> wrote:
> Le 30/08/2014 01:36, Tom Daly a écrit :
> It sounds like you might want to try disabling aspath loop
> detection for
> eBGP. Checkout the bird option called "allow local as [number]" as
> documented at
> <http://bird.network.cz/?get_doc&f=bird-6.html#ss6.2>. This
> will allow you to import prefixes with your own ASN in the aspath.
> However, one possible pitfall is that your upstream ISP's router
> try to be smart - and not send prefixes with your aspath in them
> Older Foundry boxes do this and there is a per BGP peer knob you
> have to
> Overall, this should let you run everything over eBGP and run
> two simple
> island networks.
> Unfortunately proper ISPs make their job good and does not advertise
> your own route. I have a Pop in the same configuration of yours.
> Two solution : IBGP in a GRE tunnel, it's uggly, but It works.
> Or static route :)
> Raphael Mazelier
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