[LARTC] A complicated routing scenario (for me at least)

[Warren Flemmer warren@netlab.co.za]

<PRE>Greetings

I am new to iproute2 and therefore would not try to give a direct answer to
any of your questions. I have, however, been working on what seems to me to
be a similar problem and will offer it here in case it assists.

I two have two links to the internet though different isps. The requirements
were that users on the lan would be as oblivious as possible to any one link
going down.

The solution I came up with involved two new linux boxes. Both using iproute
and one using masq (nat with 2.4 when released). One box was placed between
the two isps with source routing and a third network card linking to the
dns,www etc (I call it a crossrouter). The second box also links the two
isps and uses source routing and masq to offer redundancy (redundancy box).
An attempt at text art may help

isp1                     +redundancy box+                         isp2
|<i>                            |                             |
</I>|<i>
</I>+---------------------+                           +---------------------+
                             |                             |
                             +   Crossrouter     +
                                            |
     ---+---------+---------------+----------------------------------Lan
      www      dns                              etc


I made may attempts to use one box instead of two without any luck. I had
bad results with marking that would have made a single box solution
possible. The result was the two boxes. On the routers to the isp I have a
second default route to the redundancy box with a higher matrix. If one link
fails the data is routed to the redundancy box where it is masq on an ip
(one assigned by the isp with the good link) address and sent out through
the other isp. Every test I have done is showing the solution to work but it
has not been fully deployed yet.

I would imagine that this type of solution would be worth using is you link
to two different isps and BGP is not available. I intend doubling up on the
crossrouter as it will become a single point of failure.

If anyone knows of a better solution I would be interested to know.

Hope this helps

Regards
Warren



</PRE>