06-01-2009 05:41 AM - edited 03-04-2019 04:57 AM
All,
I understand that a confederation is a collection of ASs that are presented to an ebgp peer as one AS. I configured this with 4 routers with all of them being in their own AS:
Router1: AS100 (EBGP)
Router2: AS200 -> Presented as 500 to AS100
Router3: AS300 -> Peered with AS200
Router4: AS300 -> Peered with AS200
Okay, so all of my peerings came up correctly, but Router1 is seeing the ASPath to Router4's loopback 4.4.4.4 through AS 500 and AS 300.
Is AS300 supposed to show on Router1's bgp table?
Thanks,
John
Solved! Go to Solution.
06-01-2009 08:31 AM
Hello John,
also R3 and R4 need the commands
router bgp xx
bgp confed ident 500
bgp confed peer 200
Hope to help
Giuseppe
06-01-2009 09:05 AM
Hello John,
R3 and E4 need to know they have to write their ASN in AS confed attribute and not in main AS path attribute.
once the AS path attribute is "corrupted" R2 cannot fix it.
Hope to help
Giuseppe
06-01-2009 06:34 AM
Hello John,
with BGP confederations:
BGP AS number is the mini AS
peer BGP numbers are defined with
bgp confederation peer list of other mini ASN
the public AS (to be seen outside) requires to be defined with
bgp confederation identifier xx
So you may need these commands to achieve BGP confederation scenario.
When correctly configured only public AS should be seen by real eBGP peer.
mini ASN are placed in Confed AS path separated by AS path
public AS is placed in AS path before sending to real eBGP peer, Confed As path is stripped
Hope to help
Giuseppe
06-01-2009 06:42 AM
Giuseppe,
The confederation peers fine with the external peer, but the external peer was able to see the other external ASs that weren't peered with it.
For example, I had something like:
Router1:
ip address 192.168.1.1
as 100
neighbor Router2 remote-as 500
Router2:
ip address 192.168.1.2
ip address 192.168.3.1
ip address 192.168.4.1
AS 200
bgp confederation identifier 500
bgp confederation peer 400
bgp confederation peer 300
neighbor 192.168.1.1 remote-as 100
neighbor 192.168.3.1 remote-as 300
neighbor 192.168.4.1 remote-as 400
Router3:
AS 300
network 192.168.3.0 mask 255.255.255.0
neighbor 192.168.3.1 remote-as 200
Router4:
AS400
network 192.168.4.0 mask 255.255.255.0
neighbor 192.168.4.1 remote-as 200
The above is all from memory, so I may be missing something, but this is the gist of it. If you did a "sh ip bgp" on Router 1, you would see something like:
Network Peer AS Path
*>192.168.4.0 192.168.1.2 500 400
Thanks,
John
06-01-2009 08:31 AM
Hello John,
also R3 and R4 need the commands
router bgp xx
bgp confed ident 500
bgp confed peer 200
Hope to help
Giuseppe
06-01-2009 08:35 AM
Ah. So the peers that are part of the confederation will still go out as their own AS if they're not configured the same way the router is that's peering with the ebgp peer? I guess that makes sense. I'll play with it tonight and let you know tomorrow.
Thanks Giuseppe!
John
06-01-2009 09:05 AM
Hello John,
R3 and E4 need to know they have to write their ASN in AS confed attribute and not in main AS path attribute.
once the AS path attribute is "corrupted" R2 cannot fix it.
Hope to help
Giuseppe
06-02-2009 05:37 AM
Adding "bgp confederation peers" and "bgp confederation identifiers" to every AS solved the problem Giuseppe. Thanks!
John
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