From: Hans None (acsyao@hotmail.com)
Date: Tue Jun 14 2005 - 12:35:50 GMT-3
if you get more tries, you will find out it is not always the case. it seem
that the bgp next hop from equal metric igp is not predictable.
>From: richard.bennett@brookemead-services.co.uk
>Reply-To: richard.bennett@brookemead-services.co.uk
>To: "Hans None" <acsyao@hotmail.com>
>CC: richard.bennett@brookemead-services.co.uk, ccielab@groupstudy.com
>Subject: RE: [Fwd: Re: bgp next hop if igp load balancing]
>Date: Mon, 13 Jun 2005 23:17:42 +0100 (BST)
>
>Here is the answer: There are two equal cost routersin the routing table,
>the one with the highest IP is used in the BGP table:
>router bgp 65001
> bgp log-neighbor-changes
> network 1.0.0.0
> neighbor 11.0.0.2 remote-as 2
>
>r4#sh ip route
>Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
> D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
> N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
> E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
> i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS
>level-2
> ia - IS-IS inter area, * - candidate default, U - per-user static
>route
> o - ODR, P - periodic downloaded static route
>
>Gateway of last resort is not set
>
>O 1.0.0.0/8 [110/74] via 10.0.0.1, 00:04:08, Serial0
> [110/74] via 10.0.0.3, 00:04:08, Serial0
> 10.0.0.0/24 is subnetted, 1 subnets
>C 10.0.0.0 is directly connected, Serial0
> 11.0.0.0/24 is subnetted, 1 subnets
>C 11.0.0.0 is directly connected, Serial0.1
>r4#sh ip bgp
>BGP table version is 2, local router ID is 10.0.0.4
>Status codes: s suppressed, d damped, h history, * valid, > best, i -
>internal
>Origin codes: i - IGP, e - EGP, ? - incomplete
>
> Network Next Hop Metric LocPrf Weight Path
>*> 1.0.0.0 10.0.0.3 74 32768 i
>r4#sh ip bgp 1.0.0.0
>BGP routing table entry for 1.0.0.0/8, version 2
>Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Advertised to non peer-group peers:
> 11.0.0.2
> Local
> 10.0.0.3 from 0.0.0.0 (10.0.0.4)
> Origin IGP, metric 74, localpref 100, weight 32768, valid, sourced,
>local,
> best
>r4#
>
>
>But on the eBGP peer of course the next hop is this routers bgp
>update-source.
>
>
>
>
>
>
> > here is what i mean:
> >
> >
> >
> > on router A:
> >
> > route 10.0.0.0 has two next hops 1.1.1.1 and 2.2.2.2
> >
> > route 10.0.0.0 has to be advertised by bgp on router A
> >
> > router bgp 65000
> > no auto
> > no sync
> > network 10.0.0.0 mask 255.255.255.0
> >
> >
> > when I show ip bgp on router A, what will be 10.0.0.0's next hop?
>1.1.1.1
> > or
> > 2.2.2.2?
> >
> >
> >
> >>From: richard.bennett@brookemead-services.co.uk
> >>Reply-To: richard.bennett@brookemead-services.co.uk
> >>To: ccielab@groupstudy.com
> >>Subject: [Fwd: Re: bgp next hop if igp load balancing]
> >>Date: Mon, 13 Jun 2005 22:29:57 +0100 (BST)
> >>
> >>Hans - as I understand it, the networks advertised by the 'network
> >>x.x.x.x' bgp statement are advertised to EBGP peers, and when routes are
> >>advertisedto ebgp peers, the next hop is set to the ip address of the
> >>advertising peer, not the igp next hop.
> >>
> >>When eBGP routes are advertised to iBGP peers, the next-hop is
>maintained
> >>(i.e. the next hop of the eBGP peer whom advertised the route). This is
> >>often problematic as the eBGP peers IP address may not be known inside
> >> the
> >>IGP. In this case you can change the next hop to that of the iBGP
> >>routerusing the 'next-hop-self' command.
> >>
> >>hope that iswhat you are looking for
> >>
> >>Richard Bennett
> >>
> >>
> >>
> >> > All,
> >> >
> >> >
> >> > Normailly, when configuring bgp and use network command to advertise
> >> igp
> >>routes in routing table, the igp next hop will automatically carried
> >>over to
> >> > bgp.
> >> >
> >> > My question is, when igp is loadsharing and there are multiple next
> >> hop
> >>for
> >> > the igp routes, when using network command to advertise those routes,
> >>bgp will take which next hop?
> >> >
> >> >
> >> > Thanks,
> >> >
> >> >
> >> > Hans
> >> >
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