Hi everybody
I am learning IPVPN, specifically how we can use "as-override" to connect to remote ipvpn locations with just one AS; I encountered a strange situation described below:
AS2 MPLS CLOUD AS1 AS2
Soke2- f0/1--204.204.204.0/24--f0/1 PE4----R2----PE1-f1/0-- 105.105.105.0/24--f1/0-HUB5
spoke f0/1: 204.204.204.2
PE4 f0/1 : 204.204.204.4
PE f1/0: 105.105.105.1
HUB 5 f1/0: 105.105.105.5
We are using BGP between PE and CE
Above Spoke 2 is advertising 200.200.200.200/32 to HUB5 Via MPLS cloud ( PE4, R2,PE1, AS1)
Since spoke 2 and Hub both are in AS2, I have configured remove-as on PE1 so when PE1 advertises 200.200.200.200/32 to Hub5, it will replace AS 2 by AS1
I expect Hub5 to learn 200.200.200.200/32 via ebgp but i do not understand why Hub5 has to advertise back 200.200.200.200/32 to PE1
HUB5#show ip route ( learning it from PE1)
B 200.200.200.2 [20/0] via 105.105.105.1, 01:04:54
Advertising back to PE1 (105.105.105.1)
HUB5#show ip bgp neighbors 105.105.105.1 advertised-routes
*> 200.200.200.2/32 105.105.105.1 0 1 1 i
Configuration:
spoke2#show running-config | section bgp
router bgp 2
no synchronization
bgp log-neighbor-changes
network 200.200.200.2 mask 255.255.255.255
neighbor 204.204.204.4 remote-as 1
++++++++++++++
PE4#show running-config | section bgp
router bgp 1
Omitted!!
address-family ipv4 vrf Z
neighbor 204.204.204.2 remote-as 2
neighbor 204.204.204.2 activate
neighbor 204.204.204.2 as-override
no synchronization
exit-address-family
PE1#show running-config | section bgp
router bgp 1
Omitted!!
address-family ipv4 vrf INSIDE
neighbor 105.105.105.5 remote-as 2
neighbor 105.105.105.5 activate
neighbor 105.105.105.5 as-override
no synchronization
exit-address-family
HUB5#show running-config | section bgp
router bgp 2
no synchronization
bgp log-neighbor-changes
neighbor 105.105.105.1 remote-as 1
thanks
