All cable modems run a rudimentary LAN DHCP server to allow devices to access the internet without a router or switch (i.e. connecting a PC directly to a modem via ethernet, which, while possible, is never recommended unless a PC's firewall has been configured to reject all inbound traffic); however, this is completely separate from the web server cable modem's utilize for their status/config page at 192.168.100.1.
@sycohexor You may want to try logging requests via iptables, similar to the below:
/etc/firewall.user:
iptables -N LOG-modem
iptables -A INPUT -d 192.168.100.1 -j LOG-modem
iptables -A OUPUT -d 192.168.100.1 -j LOG-modem
iptables -A LOG-modem -j LOG --log-prefix "<[[--- Modem Traffic ---]]> : " --log-level 4
/etc/init.d/firewall reload
- This will log traffic to the kernel log (as well as system log)