Routing Question

From: Robert Sandilands (
Date: Fri Oct 12 2001 - 08:27:20 EST

I have the following setup, all Linux machines:

   M1 -- M2 -- M3 --- M4

M1 has as it's default gateway.
M2 is configured as a router and has as it's default gateway.
M3 is configured as a router to the Internet with default gw and
has a static route to the network with as gateway.
M4 is just a machine representing a machine on the Internet.

With this configuration all the machines can talk to all other machines
without any problems.

Now comes the problem. Let us say I add M5 that is with default
gateway This machine can talk to M3 and M4 without any
problems. It can only talk to the outside interface of M2 and can not talk
to M1 at all. This can be fixed by adding a static route to M5, but let us
say I have 200 machines that I have to add a static route to, and I would
rather fix the problem on M3 than on 200 computers.

If I traceroute from M1 -> M4 you get M1->M2->M3->M4. If I traceroute from
M3->M1 I get M3->M2->M1. If I traceroute from M4->M1 I get M4->M3->M2->M1.

If I traceroute from M5->M1, I get M5->M3->"* * *...." That is the problem
I'm trying to solve. Why is the traffic dying at M3 if it originates from
M5? And what can I do about it?

If I use ethereal to follow the packet I can see the packet going from M5 to
M3. I see no traffic generated by M3 in response to that.

Thank you.

Robert Sandilands

PS: Here is the information in another format.

M1 - - gw (M2)
M2 - - - gw (M3)
M3 - -
   - - gw, (M4)
                                            route -net gw (M2)
M4 - - route -net gw, (M3)
                                            route -net gw (M3)
M5 - - gw (M3)
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This archive was generated by hypermail 2b29 : Mon Oct 15 2001 - 21:00:45 EST