[AusNOG] AARNet AS path prepending on Equinix IX

[Ben Thompson]

Hi Nick,

Sorry, I got that output from our border router connected to the IX, to get a better picture I should have shown it from one of our core routers:

sh ip bgp 182.255.99.162/19 longer-prefixes
     Network          Next Hop            Metric LocPrf Weight Path
* i 182.255.96.0/19  103.29.52.2             64    100      0 7575 7575 i
*>i                  103.29.52.1              0    100      0 4826 7575 i
*>i 182.255.103.0/24 103.29.52.1              0    100      0 4826 7575 i

Because the AS Path is the same length from both transit and the IX, I think it is router Id being selected and thus our transit path (103.29.52.1) is being selected.

I did some digging around looking glasses and found that route-views.sydney.routeviews.org have a BGP session with AARnet and the AS Path includes 24115 which is the IX route servers ASN. I am guessing this makes the situation the same at AARNet with two routes with equal AS Path length (4826 then 56284 or 24115 then 56284), and the traffic from AARNet prefers Vocus over the IX.

Thanks,
Ben

From: AusNOG [mailto:ausnog-bounces at lists.ausnog.net] On Behalf Of Nick Pratley
Sent: Tuesday, 28 April 2015 7:08 AM
To: Nathan Brookfield
Cc: ausnog at ausnog.net
Subject: Re: [AusNOG] AARNet AS path prepending on Equinix IX


Hi Ben

Is thiss for inbound traffic from AARNet to you?

I can see that the best path for outbound from your router is already via the Equinix IX.

To fix inbound, you could try to prepend once or twice to your transit sessions, or advertise more specific routes to peering and less specific to transit.
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