strange non-trivial routing problem

[Rainer Clasen <bj@ncc.cicely.de>]

Hi!

This may be offtopic - its not debian-specific. But I'm not sure where to
ask at all (linux-net is announced as "development" list ...). I appreciate
pointers to the correct forum.


Ok, first some ASCII-art to confuse the reader ;-)


                    10base2
                      |
                      V
              NET_A    
 |--------------------------------------------- .... ---|
      |                             |        |
      |            NET_B            |        |
    BOX_A ----------------------- BOX_B     BOX_C
      |
      |NET_C       ^
      |            |
      |     <-- 100baseTX crosslink
      | 
    BOX_D


As you can see BOX_A is my 100mbit router running 2.1.125. BOX_B is 2.0.35
with masquerading stuff turned on. BOX_B has a route to NET_C via BOX_A's IP
in NET_B. BOX_C's default route points to BOX_B.

But: BOX_D can't connect/ping whatever to any IP on NET_A!! I traced a ping
to BOX_C by adding logged ACCEPT rules to BOX_A's and BOX_B's firewall: Ping
gets in to BOX_A, BOX_A sends it out to NET_A, BOX_C replies, BOX_B gets it,
and sends it out through NET_B - BUT BOX_A doesn't see it

If I telnet from BOX_D to BOX_B, I get those <unknown> syslog entries known
from half-port scanning.


Rainer

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