[c-nsp] Config question for a strange design

[Bernd]

Hi everyone!

I've got a pretty confusing network situation at a customer's site and hope
that anyone of you could guide me in the right direction...



      |                       | 
   Internet - - - GRE - - - Internet
      |                       |
      |                       |
============              ============
| Router A |              | Router B |
============              ============
      |                       |
      | Cat5                  | Leased Line
      |                       |
============              ============
| Switch 1 |--------------| Switch 2 |
============     LL       ============
      |                       |
      | Cat 5                 | Cat 5
      |                       |
============              ============
| Router C |              | Router D |
============              ============




Router A, B, C and D have iBGP peerings to each other over the two switches.
All the routers are in the same subnet (10.0.0.0/28)!!!
Router A and B are connected to the Internet. They announce the whole
netblock. The problem is, that if the leased line 
between both switches or between Switch 2 and Router B goes down, C and D
will have huge connectivity problems (of course) :-(

There is no other way to connect those routers together as there are a
couple of kilometers in between.

What would be the best solution that if a leased line goes down, packets
that come in to Router A still find their way to Router D and packets that
come in to Router B find their way to Router C?
Route Reflecting, OSPF, ...?



Thanks and kind regards,
Bernd