BGP Confederation

You can divide a single AS into multiple ASs, and then assign these multiple ASs to a single confederation of ASs. The implementation of a BGP confederation reduces the iBGP mesh size of the AS, and the confederation can still advertise as a single AS to external peers.

Each individual AS within a confederation runs fully meshed iBGP, and each individual AS within the confederation also runs eBGP connections to the other ASs inside the confederation. These eBGP peers within the confederation exchange routing information as if they used iBGP. In this way, the confederation preserves next hop, metric, and local preference information. To the outside world, the confederation appears to be a single AS.

BGP Confederation Configuration

To configure a BGP Confederation:

R1:

router bgp 2000
: bgp log-neighbor-changes
: bgp confederation identifier 200
: bgp confederation peers 1000
: neighbor 2003::1 remote-as 1000
!
address-family ipv4
: neighbor 2003::1 activate
exit-address-family
!
address-family ipv6
: network 3002::/64
: network 4000::/64
: neighbor 2003::1 activate
exit-address-family
On R2:
router bgp 1000
: bgp confederation identifier 200
: neighbor 10.0.1.1 remote-as 1000
!
address-family ipv6
: neighbor 10.0.1.1 activate
exit-address-family
 
On R3:
router bgp 1000
: bgp confederation identifier 200
: bgp confederation peers 2000
: neighbor 10.0.1.2 remote-as 1000
: neighbor 3001::1 remote-as 2000
: neighbor 5000::1 remote-as 100
: neighbor 5000::1 update-source X2
!
address-family ipv6
: neighbor 10.0.1.2 activate
: neighbor 3001::1 activate
: neighbor 5000::1 activate
exit-address-family
 
On R5:
router bgp 100
: bgp router-id 5.5.5.5
: bgp log-neighbor-changes
: neighbor 2002::1 remote-as 200
!
address-family ipv6
: network 6666::6/128
: network 7777::7/128
: neighbor 2002::1 activate
exit-address-family
 

Verify that R1, R2, and R3 can learn this route that is advertised by R5:

6666::6/128 and 7777::7/128

Verify that R2 can learn this route from R1 even though they are not directly connected:

3002::/64 and 4000::/64
 
* 
NOTE: The IPv6 BGP configuration data and the IPv6 BGP routes are dumped into a Terminate and Stay Resident (TSR) file.
* 
NOTE: IPv6 BGP uses the ZebOS debug interface. The default setting for all debug switches is closed. Entering the CLI debug command on the console opens the debug switch.