From: richard.bennett@brookemead-services.co.uk
Date: Mon Jun 13 2005 - 19:17:42 GMT-3
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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