From: Brian McGahan (brian@cyscoexpert.com)
Date: Fri Jul 04 2003 - 15:18:11 GMT-3
Not necessarily. As long as one side of the connection has a
longer match than 0.0.0.0/0 adjacency can be established. Take the
following scenario:
R1-16.0.0.0/8---R6---26.0.0.0/8---R2
R1 is in AS 1, R2 is in AS 2. They are transitting R6 to peer.
The only route that R1 has to the 26.0.0.0/8 subnet is a default, while
R2 has a longer match to 16.0.0.0/8.
R1#sh run | b router bgp
router bgp 1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
neighbor 26.0.0.2 remote-as 2
neighbor 26.0.0.2 ebgp-multihop 255
!
ip route 0.0.0.0 0.0.0.0 16.0.0.6
R2#sh run | b router bgp
router bgp 2
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
neighbor 16.0.0.1 remote-as 1
neighbor 16.0.0.1 ebgp-multihop 255
!
ip route 16.0.0.0 255.0.0.0 26.0.0.6
R1#sh ip bgp sum | b Neighbor
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
State/PfxRcd
26.0.0.2 4 2 11 11 3 0 0 00:06:32
1
R2#sh ip bgp sum | b Neighbor
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
State/PfxRcd
16.0.0.1 4 1 12 12 3 0 0 00:07:10
1
R1#sh ip bgp
BGP table version is 3, local router ID is 16.0.0.1
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
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 26.0.0.2 0 0 2 i
R2#sh ip bgp
BGP table version is 3, local router ID is 26.0.0.2
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
*> 1.1.1.1/32 16.0.0.1 0 0 1 i
*> 2.2.2.2/32 0.0.0.0 0 32768 i
R1#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, 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 16.0.0.6 to network 0.0.0.0
C 16.0.0.0/8 is directly connected, FastEthernet0/6
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
B 2.2.2.2 [20/0] via 26.0.0.2, 00:06:08
S* 0.0.0.0/0 [1/0] via 16.0.0.6
R1#
R2#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, 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
S 16.0.0.0/8 [1/0] via 26.0.0.6
1.0.0.0/32 is subnetted, 1 subnets
B 1.1.1.1 [20/0] via 16.0.0.1, 00:06:55
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
C 26.0.0.0/8 is directly connected, FastEthernet0/6
As you can see from the above output, as long as one side has a
longer match than 0, BGP adjacency can be established.
HTH,
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
Toll Free: 866.CyscoXP
Fax: 847.674.2625
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Scott Morris
> Sent: Friday, July 04, 2003 8:57 AM
> To: 'Donny MATEO'; 'Volkov, Dmitry (IDS Canada)'
> Cc: ccielab@groupstudy.com; nobody@groupstudy.com
> Subject: RE: BGP peer establishment
>
> There must be a non-default route to reach the other side. So
anything
> other than a 0/0 route will work.
>
> Scott
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Donny MATEO
> Sent: Friday, July 04, 2003 1:58 AM
> To: Volkov, Dmitry (IDS Canada)
> Cc: 'ccielab@groupstudy.com'; nobody@groupstudy.com
> Subject: Re: BGP peer establishment
>
>
> If I remember correctly there was an old thread discussing this. The
> conclusion is something like BGP need specific route to establish
> peering. Not sure if there is anymore information as to why and so on.
>
> Donny
>
>
>
>
>
> "Volkov, Dmitry
>
> (IDS Canada)" To:
> "'ccielab@groupstudy.com'" <ccielab@groupstudy.com>
>
> <dmitry_volkov@ca cc:
>
> .ml.com> Subject: BGP peer
> establishment
> Sent by:
>
> nobody@groupstudy
>
> .com
>
>
>
>
>
> 07/04/2003 06:22
>
> AM
>
> Please respond to
>
> "Volkov, Dmitry
>
> (IDS Canada)"
>
>
>
>
>
>
>
>
>
> R5(172.50.50.5)---------(.1)pix(.10)--------(172.50.10.1)R1
>
> R5 can ping R1; R5 uses default route to reach R1. R5 can not
establish
> BGP peering with R1 until I put static route - more specific than
> 0.0.0.0 0.0.0.0 - WHY ?
>
> r5#sh ip bgp sum
> BGP router identifier 60.5.5.5, local AS number 55
> BGP table version is 1, main routing table version 1
>
> Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
> State/PfxRcd
> 172.50.10.1 4 65 0 0 0 0 0 never
> Active
>
> r5#sh ip ro
> <snip>
> R* 0.0.0.0/0 [120/1] via 172.50.50.1, 00:00:06, FastEthernet0/0
>
> r5#conf t
> Enter configuration commands, one per line. End with CNTL/Z.
> r5(config)#ip route 172.50.10.1 255.255.255.255 172.50.50.1
>
> 00:55:02: %BGP-5-ADJCHANGE: neighbor 172.50.10.1 Up bgp ev
>
> r5#sh ip bgp sum
> BGP router identifier 60.5.5.5, local AS number 55
> BGP table version is 1, main routing table version 1
>
> Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
> State/PfxRcd
> 172.50.10.1 4 65 5 5 1 0 0 00:02:01
> 0
> r5# sh ip ro
> <snip>
>
> S 172.50.10.1/32 [1/0] via 172.50.50.1
> R* 0.0.0.0/0 [120/1] via 172.50.50.1, 00:00:13, FastEthernet0/0
>
> r5#
> router bgp 55
> bgp log-neighbor-changes
> neighbor 172.50.10.1 remote-as 65
> neighbor 172.50.10.1 ebgp-multihop 2
> r1#
> router bgp 65
> bgp log-neighbor-changes
> neighbor 172.50.50.5 remote-as 55
> neighbor 172.50.50.5 ebgp-multihop 2
>
> Thank You,
>
> Dmitry Volkov
> CCIE # 10292
>
>
>
This archive was generated by hypermail 2.1.4 : Wed Aug 06 2003 - 06:52:24 GMT-3