Debian boxes not replying to multicast and broadcast pings

[Urs Thuermann <urs@isnogud.escape.de>]

I have currently 4 Linux machines in my network, one embedded system
running Linux-2.4.20, a system build from scractch over the last 13
years running 2.4.34.2 and two Debian boxes, both running Debian's
Linux kernel 2.6.18-4-686.

When I ping to the broacast address or the allhosts multicast address
I get replies from the embedded and the self-built sysem, but not from
the two Debian boxes:

    janus:urs$ ping -w2 10.0.0.255
    PING 10.0.0.255 (10.0.0.255): 56 octets data
    64 octets from 10.0.0.1: icmp_seq=0 ttl=64 time=0.2 ms
    64 octets from 10.0.0.31: icmp_seq=0 ttl=64 time=0.7 ms (DUP!)
    64 octets from 10.0.0.1: icmp_seq=1 ttl=64 time=0.1 ms
    64 octets from 10.0.0.31: icmp_seq=1 ttl=64 time=0.6 ms (DUP!)
    
    --- 10.0.0.255 ping statistics ---
    2 packets transmitted, 2 packets received, +2 duplicates, 0% packet loss
    round-trip min/avg/max = 0.1/0.4/0.7 ms
    janus:urs$ ping -w2 224.0.0.1 
    PING 224.0.0.1 (224.0.0.1): 56 octets data
    64 octets from 10.0.0.1: icmp_seq=0 ttl=64 time=0.3 ms
    64 octets from 10.0.0.31: icmp_seq=0 ttl=64 time=0.9 ms (DUP!)
    64 octets from 10.0.0.1: icmp_seq=1 ttl=64 time=0.1 ms
    64 octets from 10.0.0.31: icmp_seq=1 ttl=64 time=0.6 ms (DUP!)
    
    --- 224.0.0.1 ping statistics ---
    2 packets transmitted, 2 packets received, +2 duplicates, 0% packet loss
    round-trip min/avg/max = 0.1/0.4/0.9 ms

The two Debian machines do reply to unicast pings, however:

    janus:urs$ ping -c1 blue
    PING blue.isnogud.escape.de (10.0.0.2): 56 octets data
    64 octets from 10.0.0.2: icmp_seq=0 ttl=64 time=1.6 ms
    
    --- blue.isnogud.escape.de ping statistics ---
    1 packets transmitted, 1 packets received, 0% packet loss
    round-trip min/avg/max = 1.6/1.6/1.6 ms
    janus:urs$ ping -c1 mop 
    PING mop.isnogud.escape.de (10.0.0.65): 56 octets data
    64 octets from 10.0.0.65: icmp_seq=0 ttl=64 time=0.3 ms
    
    --- mop.isnogud.escape.de ping statistics ---
    1 packets transmitted, 1 packets received, 0% packet loss
    round-trip min/avg/max = 0.3/0.3/0.3 ms

Also, I have written two small test programs, udp-ping and udp-echo,
which send short packets two a specified UDP port and echo all packets
to a certain UDP port, respectively.  If I send UDP packets to the
multicast address, udp-echo will answer, also on the Debian machines.
This shows that the Debian machines are able to receive multicast.

So what is the reason, that the 2.6.18-4-686 kernel does not reply to
ICMP echo request to broadcast and multicast address?  I've looked
through /proc/net and /proc/sys/net but haven't found anything which
looked relevant.

urs