From: Carlos G Mendioroz (tron@xxxxxxxxxxx)
Date: Sat Jul 06 2002 - 07:53:17 GMT-3
Hunt,
Would you take a look at wich router is initiating the connection ?
I would guess it's RTA.
I would guess that the implementation of this has two parts:
update-source telles the router to initiate the call (tcp connection
to neighbour) from the stated IP, and enables BGP listening on that
IP. But actually checking that a connection from a given neighbour
comes from the programmed remote IP is not performed.
So if RTA calls 172.16.1.3, the call is accepted (because you have
"enabled" BGP processing with nei neighbor 172.16.1.2 update-source
Loopback0)
and then you have 172.16.1.1 - 172.16.1.3 which is ok.
But were RTB to call RTA, it would call originating in 10.1.1.2, which
would not work. (Can check this by setting some filter)
Also, if you take down the RTB-RTC config I guess it would also not
work.
(because you would be disabling BGP for the loop 0 int)
Anyways, this also could be IOS dependant, so I would stick to setting
it
up simetrical...
Hunt Lee wrote:
>
> Group,
>
> I have a BGP question and the scenario is as follows.What am i doing
> wrong ? Scenario is:
>
> RTA -- RTB -- RTC
>
> They are all in the same AS 1.
>
> RTA's Serial: 10.1.1.1
> RTB's Serial: 10.1.1.2 (connecting to RTA)
> RTB's Serial: 10.1.2.1 (connecting to RTC)
> RTC's Serial: 10.1.2.2
>
> Each Router also has a Loopback Interface for IBGP connection.
>
> RTA's Loopback0: 172.16.1.1
> RTB's Loopback0: 172.16.1.3
> RTC's Loopback0: 172.16.1.2
>
> Ok - what I am confused is the BGP command "neighbor x.x.x.x
> update-source <interface x>"?? My understanding of the command is
> that the router who used this command can specify another interface
> to be used for IBGP Neighbor connections.
>
> So at here, RTA will tell RTB (172.16.1.3) to use RTA's Loopback
> interface for IBGP session.
>
> RTA:-
>
> router ospf 1
> log-adjacency-changes
> network 10.1.0.0 0.0.255.255 area 0
> network 172.16.1.1 0.0.0.0 area 1
> !
> router bgp 1
> bgp log-neighbor-changes
> network 1.0.0.0 mask 255.128.0.0
> neighbor 172.16.1.3 remote-as 1
> neighbor 172.16.1.3 update-source Loopback0
>
> RTB:-
>
> router ospf 1
> log-adjacency-changes
> network 10.1.0.0 0.0.255.255 area 0
> network 172.16.1.3 0.0.0.0 area 3
> !
> router bgp 1
> no synchronization
> bgp log-neighbor-changes
> neighbor 172.16.1.1 remote-as 1
> neighbor 172.16.1.1 route-reflector-client
> neighbor 172.16.1.2 remote-as 1
> neighbor 172.16.1.2 update-source Loopback0
> neighbor 172.16.1.2 route-reflector-client
>
> But at RTB, there is no neighbor update-source statement pointing
> back to RTA. Nevertheless, the BGP session still managed to get
> established. How can BGP still managed to establish the BGP
> connection??
>
> RouterB#sh ip bgp summary
> BGP router identifier 172.16.1.3, local AS number 1
> BGP table version is 3, main routing table version 3
> 2 network entries and 2 paths using 266 bytes of memory
> 1 BGP path attribute entries using 60 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 activity 4/4 prefixes, 4/2 paths, scan interval 15 secs
>
> Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
> State/PfxRcd
> 172.16.1.1 4 1 15 13 3 0 0 00:03:52 1
> 172.16.1.2 4 1 14 14 3 0 0 00:04:17 1
> RouterB#
>
> Or is this command only required for EBGP sessions? Anyone with
> ideas.
>
> =====
> Thanks in advance for ur time and replies.
> Hunt
>
> http://www.sold.com.au - SOLD.com.au
> - Find yourself a bargain!
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