Quote:
Originally Posted by KingDaveRa
The modems are layer 2 devices then? They have the local management IP on them, which I can see, but I'm guessing Virgin can't. Unless there's another IP on the network-facing side.
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Yep that's why they're modems not routers
The modems do have an IP address reachable on the network facing side, they grab one for their own use for downloading their configuration file, etc, on some kit you see the modem's gateway when you ping your first hop. Your traffic doesn't go through that hop it's just where some kit responds from. The modems' network facing connectivity is purely a layer 2 interface.
Cable downstream, remember, is a broadcast medium. All modems in a segment see all traffic. The Virgin kit switches traffic at layer 2 to customers' PCs but this is actually a broadcast, similar to an old school hub, on the physical cable. If a modem doesn't have that MAC address behind it it simply drops the traffic, if it does it switches the traffic to your PC / router. Likewise if the traffic is destined to the 10.x address the modem took at boot up it'll do the necessary.