Additional bgp route

Unanswered Question
Nov 8th, 2007

Dear all,

I am doing some bgp lab practise, once i finished the bgp configuaration on one router, observe there is one additional bgp route appear in the routing table. Could you give some idea why that happened? Thank you.

Vail#sh ip ro

Codes: C - connected, S - static, 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

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

B 192.168.200.0/24 [20/2195456] via 192.168.1.225, 00:08:46

192.168.255.0/32 is subnetted, 1 subnets

C 192.168.255.254 is directly connected, Loopback0

192.168.1.0/24 is variably subnetted, 4 subnets, 2 masks

B 192.168.1.0/24 [20/2169856] via 192.168.1.225, 00:08:46

C 192.168.1.224/30 is directly connected, Serial1/1.2 <<<<<(Why have this route)

B 192.168.1.216/30 [20/0] via 192.168.1.225, 00:08:46

C 192.168.1.220/30 is directly connected, Serial1/1.1

B 192.168.100.0/24 [20/0] via 192.168.1.225, 00:08:46

Vail#

Vail#sh ip int brief

Interface IP-Address OK? Method Status Protocol

Serial1/0 unassigned YES TFTP up down

Serial1/0.1 unassigned YES NVRAM up down

Serial1/0.2 unassigned YES NVRAM deleted down

Serial1/1 unassigned YES TFTP up up

Serial1/1.1 192.168.1.221 YES manual up up

Serial1/1.2 192.168.1.226 YES manual up up <<<<<<<<<<<<<<<<

Serial1/2 unassigned YES NVRAM administratively down down

Serial1/3 unassigned YES NVRAM administratively down down

Loopback0 192.168.255.254 YES manual up up

Vail#

Vail#sh ip b

BGP table version is 7, local router ID is 192.168.255.254

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 192.168.1.0 192.168.1.225 2169856 0 200 ?

*> 192.168.1.216/30 192.168.1.225 0 0 200 ?

r> 192.168.1.224/30 192.168.1.225 0 0 200 ? <<<<<<<<<<<<<

*> 192.168.100.0 192.168.1.225 0 0 200 ?

*> 192.168.200.0 192.168.1.225 2195456 0 200 ?

Vail#

Vail#sh run int s1/1.2

Building configuration...

Current configuration : 121 bytes

!

interface Serial1/1.2 point-to-point

ip address 192.168.1.226 255.255.255.252

frame-relay interface-dlci 311

end

Vail#

Vail#sh ip b s

BGP router identifier 192.168.255.254, local AS number 100

BGP table version is 7, main routing table version 7

5 network entries using 585 bytes of memory

5 path entries using 260 bytes of memory

4/3 BGP path/bestpath attribute entries using 496 bytes of memory

1 BGP AS-PATH entries using 24 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 1365 total bytes of memory

BGP activity 11/6 prefixes, 11/6 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

192.168.1.222 4 100 42 50 7 0 0 00:10:05 0

192.168.1.225 4 200 90 82 7 0 0 00:10:05 5 <<<<<<<<<<<<<<<<<<

Vail#

I have this problem too.
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Kevin Dorrell Fri, 11/09/2007 - 00:31

Does your EBGP neighbor (192.168.1.225) have a statement like network 192.168.1.224 mask 255.255.255.252? 'Cos that is where it is coming from to get into the BGP table. We need to see the configuration of the AS 200 neighbor.

However, it is not the BGP route that is getting into your forwarding table. That is getting overwritten with the directly connected route at AD=0.

Kevin Dorrell

Luxembourg

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