Weird routing in potato

[Phil Carmody <fatphil@altavista.com>]

I have a heterogenous network within a /28 number space, a.b.c.[48-63]

windows   .51 --|H|
debianx86 .52 --|U|-- Firewall .62 -- DSL
debianx86 .56 --|B|
                /
debalpha  .54  /      Broadcast address .63

My alpha 2.2.18Pre21 has problems seing the other three machines, and the three machines have problems seeing the alpha.

<<<
bash-2.03$ ping a.b.c.54
PING a.b.c.54 (a.b.c.54): 56 data bytes

--- a.b.c.54 ping statistics ---
7 packets transmitted, 0 packets received, 100% packet loss
>>>

All three debians have the following `route -n`

<<<
Destination Gateway  Genmask         Flags Metric Ref Use Iface
a.b.c.48    0.0.0.0  255.255.255.240  U     0      0    0 eth0
0.0.0.0     a.b.c.62 0.0.0.0          UG    0      0    0 eth0
>>>

(I tried removing all routing, and adding them one by one, but that resulted in no change)

All 4 machines can see the outside world without any trouble at all.

The really bizarre thing is when I ping the broadcast address (either .48 or .63) from one of the x86 boxes:

<<<
bash-2.03$ ping a.b.c.63
PING a.b.c.63 (a.b.c.63): 56 data bytes
64 bytes from a.b.c.56: icmp_seq=0 ttl=255 time=0.1 ms
64 bytes from a.b.c.52: icmp_seq=0 ttl=255 time=7.2 ms (DUP!)
64 bytes from a.b.c.56: icmp_seq=1 ttl=255 time=0.0 ms
64 bytes from a.b.c.52: icmp_seq=1 ttl=255 time=0.1 ms (DUP!)
64 bytes from a.b.c.56: icmp_seq=2 ttl=255 time=0.0 ms
64 bytes from a.b.c.52: icmp_seq=2 ttl=255 time=0.1 ms (DUP!)
64 bytes from a.b.c.54: icmp_seq=2 ttl=255 time=940.4 ms (DUP!)
>>>

So the alpha at .54 has responded!
(Note that a broadcast ping from the alpha does not get replies from any of the other machines, only this way round)

I'm very very confused. I've read every book (on Linux and Unices generally) and manpage (on routing and network related configuration), gone to single user mode, ad pulled every part of the system up in excruciating fine-grained steps, and I've solved nothing. Does anyone have any ideas?

For reference - everything has worked well for the last year - I powered the machine down for 10 minutes 2 days ago, and on reboot the thing just stopped talking to the x86 part of my computer room.

Help!
(please :-) )

Phil

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