Further to my previous post:

+Every 3 minutes I get a multicast IGMP packet. The destination
+is the 'all-hosts' group 224.0.0.1 and the source is always
+the private class C address: 192.168.100.1, which is not used on my
internal
+network. Anyone know if T/S routers are using IP multicasting
+for a valid purpose (perhaps they are generated by the cable
+modem itself?) Currently, my iptables based firewall rules drop
+the packets.

I have now discovered more about the origin of the above packets. The
IGMP packets are almost certainly originating from the Cable modem
itself.

The source address of these IGMP packets: 192.168.100.1 was bugging me a
bit, so just for the hell of it I did a port scan on that address. To my
surprise this showed ports 80, 389, 513 and 1002 open. Hmmmmm port 80
looked interesting so I went to a browser and entered
http://192.168.100.1 and guess what: I received a web page entitled
'Configuration Manager' with a side-bar containing a 'Surf Board' logo
(the brand name of the cable modem). The cable modem is a SURFboard
(Motorola SB3100i). This web admin interface provides access to status,
configuration and log viewing functions. An 'Addresses' page reveals
that the IP address for the cable modem is in fact 192.168.100.1 (can be
configured to be other address on the 192.168.100 subnet). Of course,
none of this stuff is mentioned in the printed 'User Guide' that comes
with the CM.

I am still none the wiser as to what functionality this is supposed to
provide given that the multicast is always active. Nor could I find any
configuration option in the web admin interface to turn it on or off or
any mention of it in the online help. Anyone know more about this? At
least now that I know the CM is doing this multicast It will make it
easier to search the net for more info on it.

 
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Received on Sun Jan 13 13:25:27 2002