From: Craig Dorry (chdorry@yahoo.com)
Date: Sun Jul 06 2003 - 16:13:50 GMT-3
The reason for not using the default route when
forming BGP peers via eBGP multihop is to ensure that
no routing loops are accidentally introduced during
times of instability/convergence.
Per Cisco's webpage:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/np1_c/1cprt1/1cbgp.htm
You will see the following Note:
Note To avoid the accidental creation of loops
through oscillating routes, the multihop session will
not be established if the only route to the multihop
peer's address is the default route (0.0.0.0).
Hope this helps.
--- Brian Dennis <brian@5g.net> wrote:
> A router will not use a default route to reach
> another BGP peer. Also as
> a side note a router will not use a default route to
> determine if the
> next-hop address of a BGP route is reachable.
>
> If for some reason you want to use a "default route"
> do this:
>
> ip route 0.0.0.0 128.0.0.0 Ethernet0/0
> ip route 128.0.0.0 128.0.0.0 Ethernet0/0
>
> This is the next best thing to a default route and
> it'll work for BGP to
> determine is a next-hop address of a route is
> reachable. ;-)
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
>
> -----Original Message-----
> From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com] On Behalf Of
> Volkov, Dmitry (IDS Canada)
> Sent: Thursday, July 03, 2003 3:22 PM
> To: 'ccielab@groupstudy.com'
> Subject: BGP peer establishment
>
>
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 - 06:52:26 GMT-3