BGP Multihoming - ISP B interface IP not reachable from outside

[mhrznamn]

We have BGP peering with two ISP's  (ISP A and ISP B). Both the ISP's are connected on a same border Router on different interface. Both  ISP are directly connected and connected routes can be seen in routing table.

We are receiving  default-routes from both the ISP's. We have advertised our IP prefix to both the ISP's (103.XX.XX.XX/24) subscribed from APNIC . We have configured route-map and called in  bgp neighbor to make ISP A as primary.

interface gig 0/0/0

des. ISP A

ip address xxx.xxx.xxx

interface gig 0/0/1

des. ISP B

ip address xxx.xxx.xxx

route-map ISPB-in permit 10
set local-preference 80

route-map ISPB-out permit 10
set as-path prepend 132407 132407 132407 132407

Above route map has been called to bgp neighbor with ISP B

Now, the problem we are facing is we are not able to ping IP of interface gig 0/0/1 from internet, where IP of ISP B has been configured  . 

Howerver the ping is reachable from outside  if the  interface gig 0/0/0 ( ISP A) is shutdown. 

[r.maharjan · Accepted solution]

Hi Aman,

Your issue should be related to what source ip it is being taken while reaching your internet ip. Seems your p2p ip for connecting ISPs is their own ip address. Since your default route is preferred via ISP-A, your router will always reply via ISP-A when replying your packet. Hence in that packet, your source ip will be of an ip address of ISP-B. Since your ISP-A can't accept sourced ip address of ISP-B, it may be dropping your packet. 

When you are shutting down ISP-A, your default gateway is via ISP-B hence your reply packet is via ISP-B and your ip address is of ISP-B too, hence symmetric and ISP-B will certainly pass its own sourced ip address. 

Hence my suggestion would be to use your own ip address for p2p. But this must not affect your own public ip address network traffic.