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gmsmstr
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Multihome - nonp-prepended BGP

Fri Dec 04, 2009 6:49 am

Intresting action here.. Two ISPs , two MikroTik Routers. Each one is receving one providers full BGP tables. Both routers have 4 differant prefixes listed to advertise (all setup with NO for sync).

This works fine, and if you reboot one MT, everything is fine, all traffic hops to second MT, great. Somtimes on provider B, the BGP session drops, and then immediatly reconnects and starts receiving routes. The issue, is that the prefixes (again both provider A and B are sending out the same prefixes without prepends), these prefixes completly disapear from the internet routing table! I.e. even though Provider a is still connected and never lost a BGP session, all inbound traffic stops, and on other BGP MTs in the planet, their Prefixes are NOT shown, until we do a resend all on Provder A.

Thoughts, suggestions?
 
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Re: Multihome - nonp-prepended BGP

Fri Dec 04, 2009 8:43 am

did the route flap enough times that its getting dampened and not annouced out the other provider? Do you know about BGPlay? It's a good tool to see what your annoucement looks like at any given time (over the past 30 days). google "bgplay" and enter your prefix and poke around and see if you can tell whats happening.

if you enter '/routing bgp advertisements print <peer>' do you see any prefixes listed twice? Just curious.
 
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gmsmstr
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Re: Multihome - nonp-prepended BGP

Fri Dec 04, 2009 5:24 pm

I don't see them twice, even though they should be. The BGPlay, is kewl btw, but shows all traffic hopping off of provider B to provider A, and then a bunch of lines go away like prefixes or seomthing is not being annouced, what is happening.

I also don't see them twice in the annoucments, remember two peers on two differant boxes.
 
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Re: Multihome - nonp-prepended BGP

Fri Dec 04, 2009 8:04 pm

I wondered if your two boxes were using ibgp between each other to exchange routes. If the one route was redistributed (other bgp) then maybe it got withdrawn from the other provider along with that ibgp withdraw. I saw that happen on mine recently when using the 'networks' tab to force an annoucement. Thus the wondering if you saw it twice, one with 'icomplete' and another with 'igp' or something like that.

if you want help analyzing the bgplay results I've gotten pretty good at it. email me the prefix and date range if you want help.

what version of routeros? I'm still using 2.9.51 because i never trusted 3.x/4.x bgp (little testing).

Sam
 
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Re: Multihome - nonp-prepended BGP

Fri Dec 04, 2009 9:36 pm

Eventually we want to do that, select the best path based on AS cost. Right now though, we are only running ospf between the two. ..

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