<i>Is this a cable modem or a router?</i><p>Reminds me of the inane SNL sketch, whose catchphrase was: &quot;New Shimmer is both a floor wax and a dessert topping!&quot;<p>My Arris (nee Motorola) SB6141 is a bridge and a router. It&#x27;s actually very nicely done.<p>When the modem can&#x27;t access the cable infrastructure, it turns itself into a DHCP server and hands out IP addresses in the range 192.168.100.xx. This is useful for people at home whose configurations are such that their home networks won&#x27;t work properly without some sort of DHCP server provided by the ISP.<p>Once the modem can talk to the ISP, it turns itself into a bridge. The IP addresses the modem previously issued were valid for 30 seconds, so there will shortly be a new DHCPREQUEST which the modem bridges out to the ISP. From then on, the modem is transparent to IP traffic (but see below).<p><i>My definition of cable modem doesn&#x27;t include an IP address.</i><p>This is highly useful. Once the modem has switched to being a bridge, it still responds to 192.168.100.1. There&#x27;s all sorts of useful information there. E.g. DOCSIS status, Channel IDs, received Signal to Noise ratio, transmit Power Level, etc. There&#x27;s even a nice (but short) log of the modem&#x27;s interaction with the cable infrastructure.<p>The modem is outside my firewall, so I don&#x27;t really worry about it much. It&#x27;s like anything else on the Internet as far as my home network is concerned.<p>However, I do currently allow access to 192.168.100.1 (normally I block outbound RFC 1918 addresses). That is a potential problem should some rogue program on my network attempt to exploit a modem vulnerability. Maybe I&#x27;ll just block all those addresses and only enable them in the firewall when I want to check the modem status.