[nsp] Routing based on TCP status

[odusseus]

Hi,

I have 5 routers A,B,C,D,E connected as a cercle:

A-----B--------C
|                       |
E---------------D

A & B = AS 1.
C,D,E = AS 2.

A and B are running OSPF and iBGP.

The eBGP session is running between A and D

C,D and E are running OSPF.
E and C are route reflector clients of D.

The way the routing is done makes traffic going:

- From A to D via B and C
- From D to A via E.

The router B as a kind of "floating" loopback interface with the *same* IP address as the one of A, used for the eBGP session.
This way if the link between A and E is down, the traffic will go only like this:

- From A_lo0 to D via B and C,
- From B_floating_lo1 to D via C,
- From D to B_floating_lo1 via E.

Thus, the eBGP session will become between B and D where D is configured with only
one peer ip address == A_Lo0 == B_floating_lo1.

Till here everything is working fine, as described.

Now, I need the router D able to choose the best path not when a line is down but depending on the TCP status between him and A due to the eBGP session:

if D receives from A a TCP segment on its port 179 with the flag RST set, then D should prefer to reach A via B and C.

How can I make D making routing decision based on a TCP status?

Thank you in advance for any comment and suggestion.

Thank you.

Christophe
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