Quote:
Originally Posted by Broadbandings
Yep that's why they're modems not routers  |
Oh yeah.... duh
Quote:
Originally Posted by Broadbandings
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.
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I'd forgotten about the fact they broadcasted traffic. How big would a segment be though? I know the old thing used to be people would say it could be slow if everybody in your street were downloading, but there must be a slightly more specific level for deciding how big a segment is than just an entire street. There's about 40-odd houses in my street, yet there's others round here into the hundreds. Also, there's two types of cabs round here; there's the smaller pitched-roof ones in each street, then larger flat-roofed ones which seem to sit on the main roads. I've seen inside the smaller ones and it's just the taps, and some Krone strips for the telephones. Afaik they then all link up to the bigger ones which do the fibre coax conversion. My guess would be each segment is multiplexed into the fibre at that point, then punted up to the CMTS location where it's split back out, then fed into it. All the CMTS I've seen online have been coax-based, but I'm sure there must be some that can take the fibre coax link as is.
That's my guess anyway