[nsp] BGP question

[Stephen J. Wilcox]

Ok so yuo need to change something thats checked after the as path length. Your 
best bet is the metric (MED):

route-map prov1-feed-in permit 10
 set metric 0
route-map prov2-feed-in permit 10
 set metric 50


lowest med wins so prov1 will get the traffic all other things (inc as-path 
length being equal)

Steve

On Fri, 12 Sep 2003, Krzysztof Adamski wrote:

> 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
> > >>
> > >>
> > >> _______________________________________________
> > >> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> > >> https://puck.nether.net/mailman/listinfo/cisco-nsp
> > >> archive at http://puck.nether.net/pipermail/cisco-nsp/
> >
> > Regards,
> >
> > Mark Tinka - CCNP
> > Network Engineer, Africa Online Uganda
> >
> >
> > _______________________________________________
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> >
> 
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