Activity light on my cable modem ...?

Yea, I notice the same thing. Even with the computer off the activity light is going crazy. I guess it means nothing now.

Exactly. What you're seeing is all your neighbors traffic. However, only the traffic that's destined for your cable modems MAC address, and gets decrypted, appears at the ethernet port. Therefore, you can't put a sniffer on the ethernet port and either decrypt the traffic, or try to measure it. (There are other ways of measuring traffic such as through the JTAG port).

A good clue is the netmask of your cable connection. You'll find it on the status screen of your router or wireless router. Depending upon your cable topology (I have a wall chart from CED magazine hanging on my office wall with all the cable technologies), you can guess the number of neighbors: 255.255.255.0 254 255.255.254.0 510 255.255.253.0 1022 255.255.252.0 4046 The local Comcast system runs with 1000 users per node. Incidentally, the big CISCO CMTS boxes can handle up to 65,000 customers per box (though up to 64 remote nodes).

The more users on your segment, the slower your cable modem will run. The limitation is not much in the download speed, but in the return channel (between 5-45MHz) which tends to get clogged with outgoing traffic (servers) and polluted by ingres (RF interference). This is why the cable modem providers don't offer symmetrical or business class service suitable for servers.

Start reading here:

If home cable and DSL connections were suitable for hosting, there would be no need for big server farms, full of web hosting servers, and big fat pipes to the internet. I run a few weather stations on local DSL connections. One or two users every few days is not much of a load. That works fine. However, for the ones that are publicly accessible, I mirror it to a hosting service.

I wonder if it is reflecting the increased number of subscribers on the cable system? Ya think it can ever bog down from high traffic?

William Lee

Thanks Jeff, That is intresting information. I was reading about website hosting and wondering if the cable would suport me being the server to my website. Looks like that is not such a good idea.

William Lee

Jeff,

Do you recall which issue of CED your chart came from?

I'm on Comcast with a netmask 255.255.252.0. I think that means 4046 max users for a specific upstream freq?

Mike N6DZU

Nope. There's a foldout insert in every issue. Usually it's sponsored by some manufactory. Once a year, they include the latest cable network topology diagrams. I save them all and have about 8 years worth. It's amazing to watch how topology changes along with alliances and mergers. Anyway, you'll see some of the wall charts at the bottom of:

Comcasts hybrid dual fiber pretzel ring star/bus topology will handle up to about 4000 homes per node. Very reliable on the backbone and to the main nodes. Constipated to the max on the mini-nodes and local distribution bus.

and any broadcast packets that your ISP does't filter.

Copied from the following URL.

Host/Subnet Quantities Table Class B Effective Effective # bits Mask Subnets Hosts

------- --------------- --------- --------- 1 255.255.128.0 2 32766 2 255.255.192.0 4 16382 3 255.255.224.0 8 8190 4 255.255.240.0 16 4094 5 255.255.248.0 32 2046 6 255.255.252.0 64 1022 7 255.255.254.0 128 510 8 255.255.255.0 256 254 9 255.255.255.128 512 126 10 255.255.255.192 1024 62 11 255.255.255.224 2048 30 12 255.255.255.240 4096 14 13 255.255.255.248 8192 6 14 255.255.255.252 16384 2

Class C Effective Effective # bits Mask Subnets Hosts

------- --------------- --------- --------- 1 255.255.255.128 2 126 2 255.255.255.192 4 62 3 255.255.255.224 8 30 4 255.255.255.240 16 14 5 255.255.255.248 32 6 6 255.255.255.252 64 2

Lars

except that the Internet hasn't been using Class A, B, or C for about 12 years now. See RFC1517, RFC1518, and RFC1519. A nice table to look at is found in RFC1878

Currently, there are 66770 network assignments by the five Regional Internet Registers (AFRINIC, APNIC, ARIN, LACNIC and RIPE). Most of those networks use a binary mask:

However, that's only 64377 assignments. The remaining 2393 assignments are in 186 non-binary sizes from '36' to '12582912' addresses - the latter being a network that could be divided into 192 255.255.0.0 sized subnets. Note that only 38962 assignments world wide use what had been called Class A, B, or C.

Old guy