[nsp] Backup BGP session

[odusseus]

Hi all,

I would like to know your opinion about what follows where I would prefer not to use HSRP nor VRRP:

     AS x            .    AS y
                     .
                     .
          +---+     (1)   +---+
  +------>| A |-----------| B |
  |       +---+      .    +---+
  |         |        .         \
+-------+   |        .          +---+
| hosts |   |        .          | C |---> default route
+-------+   |        .          +---+
            |        .         /
          +---+     (2)   +---+
          | E |-----------| D |
          +---+      .    +---+
                     .
                     . 



(1) is the main line.
(2) is the backup line.

A,B,C,D,E are routers.



E has a eBGP session with C via (A,B) and get a full routing table
E has a iBGP session with A and send a full routing table.
OSPF is also running between A and E where they both redistributing their connected subnet.

E sends its traffic to C via (A,B) as it prefer this path rather than via D.
A sends its traffic to C via (B) as it prefer this path rather than via E.

Hosts sends its traffic via A 

Untill here things are working as described.


Now I would configure A and E with the *same* loopback IP address where none of them would advertise it to anybody.

E and A are having traffic to C via the preferd path (1).

Then A would have a iBGP session with C only as long as the line (1) is up.
When the line (1) is down, C would have an iBGP session with E only via the line (2).

At this point, Host would just be configured to have a default-route instead of
a default-gateway.

Thank you.

Regards,

Christophe
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