[nsp] BGP question

[Krzysztof Adamski]

That is not what Kevin asked (I have the same question).
He wants to only influance the routes with the same AS path length to
always go to provider1, but in all other cases the AS path length wins
with default behavior.

K

 On Fri, 12 Sep 2003, Mark Tinka wrote:

> Sorin CONSTANTINESCU wrote:
> > Hi,
> >
> > Kevin wanted his egress traffic (upload) to go through preferred
> > upstream, not his ingress (download) traffic.
>
> Well then, in that case, even easier; simply modify the LOCAL_PREF attribute
> of the routes learned from ISP 2, and set that value lower.
>
> Cisco defaults to 100, so you can set local preference for routes learned
> from ISP 2 [either default information, or a full BGP feed] to something
> like 80. The routes with a higher local preference, win, and get installed
> from the BGP Loc-RIB into the router's active routing table.
>
> You can do that with:
>
> route-map bgp-feed-in permit 10
>  set local-preference 80
>
> Then apply this to the inbound annoucements coming from ISP 2, the less
> prefered circuit. I'd recommend using the Route Refresh capability to effect
> the new policies :-).
>
> >
> > Mark Tinka said:
> >> cisco-nsp-bounces at puck.nether.net wrote:
> >>> I'm still a newbie at bgp, so please bear with me.
> >>> I have two links to the internet.
> >>> A lot of routes from both providers have equal AS paths.
> >>> If one bgp session gets reset all that traffic (the equal AS path
> >>> routes) goes out to provider2 and does'nt reset back to provider1,
> >>> providing that the bgp session to provider1 was the first one to
> >>> come up. I don't have any metrics, weights or localpref on any
> >>> routes. Is there any way to have those equal path routes default to
> >>> provider1 rather than provider2 if provider1's link and bgp session
> >>> are up? Right now in order to reset those routes back to provider1
> >>> I have to do a hard "clear ip bgp provider2" reset.
> >>>
> >>> Kevin,
> >>> Honeycomb Internet services
> >>
> >> Hi Kevin.
> >>
> >> You can use communities, with your ISP, to influence the path
> >> selection process. But even easier, you can make the AS path over the
> >> less preferred ISP, longer, by prepending it along with your BGP
> >> announcements to their BGP speaker.
> >>
> >> Basically, the path with the shortest AS path, wins. So, by making
> >> the AS path over ISP 2 longer, you automatically ensure it's only
> >> used for return traffic when ISP 1 is totally unavailable. You can
> >> do this by:
> >>
> >> route-map PREPEND-ISP-2 permit 10
> >>  set as-path prepend xxx xxx xxx xxx
> >>
> >> Where xxx = your own ASN. The more times you prepend your ASN, the
> >> longer the path over ISP 2 appears. IIRC, Cisco route maps will
> >> support a maximum of 10 prepends + 1 which is sent along by default.
> >>
> >> You will then need to apply this route map to your outbound policies
> >> to ISP 2, and you're in business.
> >>
> >> Regards,
> >>
> >> Mark Tinka - CCNP
> >> Network Engineer, Africa Online Uganda
> >>
> >>
> >> _______________________________________________
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>
> Regards,
>
> Mark Tinka - CCNP
> Network Engineer, Africa Online Uganda
>
>
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