[LARTC] how to do source routing in same table?

[Abraham van der Merwe <abz@frogfoot.net>]

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Hi!

I have the following setup:


          ISP 1           ISP 2
         +------         +------
            \             /
              \         /
              +----------+
              | router A |			
              +----------+
               /        \
              \   IBGP  /			   
              /          \
        +----------+  +----------+
        | router B |  | router C |
        +----------+  +----------+
              |             |
            CLIENTS      CLIENTS

Routes are distributed between router A, B, and C via IBGP. There are also
two upstream providers and we have globally routable ips which are
advertised to both providers via BGP and also some ips which are only
routable to each individual isp.

So now we have the situation where we need two default gateways on router
A (depending on source network). Usually this would be simple:

ip rule add from $ispa_net table ISPA
ip route add default via $ispa_gw table ISPA
ip route add default via $ispb_gw

and you give ISPA table a higher priority (lets say 252).

My problem now is if I get routes from router B and C via BGP, zebra adds it
to the main table, but since routing table ISPA is evaluated first and only
contains a default gateway, all packets are sent out via isp A instead of
being routed to router B.

This problem could be solved if

 (a) I could add both those default routes in the main table (e.g.
     something like this would've been perfect (if it was possible):
	 
          ip route from $ispa_net to default via $ispa_gw
          ip route from $ispb_net to default via $ispb_gw

     because then Zebra would add its routes in the same table and those
     more specific rules would be evaluated before the default routes)

 (b) Zebra added its routes into all the tables, but that would be
     riciculous (imagine adding 50000+ routes into multiple tables and
     evaluating all of them)

Anybody have any idea how I can solve this?

--

Regards
 Abraham

Watson's Law:
	The reliability of machinery is inversely proportional to the
	number and significance of any persons watching it.

___________________________________________________
 Abraham vd Merwe - Frogfoot Networks CC
 9 Kinnaird Court, 33 Main Street, Newlands, 7700
 Phone: +27 21 686 1674 Cell: +27 82 565 4451
 Http: http://www.frogfoot.net/ Email: abz@frogfoot.net


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