[lug] cable modem in the Tech Center

Archer Sully archer at meer.net
Mon Mar 6 09:42:37 MST 2000

----- Original Message -----
From: "Michael J. Hammel" <mjhammel at graphics-muse.org>

> It looks like I'm going to be getting a cable modem.  I don't know
> about these other than they work on a shared local network design, ie
> are a group of people in my area that technically have access to my box
> the time.  So, I need to know a few things.
> 1. Who provides such access?

Your cable company.  They will act as both transport provider
and ISP.  This is not a good thing.  Oh, and the shared bandwidth
effect is real.  If you remember the bad old days of 200 workstations
on a single thicknet segment, you know what cable modem is like.

> 2. What are the costs?

Not too bad.  Again, it depend on the provider.

> 3. What equipment do I need?  I have thinnet at home (yes, 10 year old 8
>    bit 3Com and WD cards running on thinnet coaxial cable).  Any problems
>    with hooking that with the cable hookup?

AFAIK, "cable modems" are usually designed to be hooked up to a single
machine, so you would need to use a (linux) box as a gateway.  They usually
do not have NAT (and certainly not MASQ),  so you'll need to gateway
anyway.   Also, check with your provider: they will probably throw in a
cheap 10baseT card and null-ether cable, which you should take on general

> 4. What security precautions should I take?  Should I get a firewall box?

When you get a cable modem, you are effectively on the internet full
time, so you need to take all available precautions.  This includes a
real passwords on your internal accounts, and regular audits of your
machines.   You will probably have script kiddies infesting your network
within minutes of hooking up (I know I did!).  So far, I haven't noticed
these guys to do a lot of harm.  I'm sure they are hiding in the cracks,

I'm currently running an insufficient filtering firewall/gateway on RH6.0
talking to a Cisco 625(?) DSL router.  I use MASQ to hide the other
machines behind the "firewall."   This is far from a perfect setup, but
if you run filtering and proxies on the firewall (which I haven't bothered
with yet) in addition to MASQ you be mostly ok.

Slow Pentiums and even a fast 486 will work for your firewall/gateway.

Be sure to read the firewall howto.  There's also howto's on IPCHAINS
that are useful.

> 5. How difficult will it be to move the service when I move from my
>    apartment into a house later this year?

Problematic.  If your cable company offers the service at both locations,
it should be a snap.  If it doesn't, you are hosed, and might need to get
DSL.  If you change cable companies because of the move, all bets are
really off.

> 6. Are there kernel requirements?  I currently run RH5.2 on my main box,
>    but I'm getting another box that I can load anything on.  I'll probably
>    KRUD, but I still want to know what OS requirements might exist for
>    cable modems.

I would update the kernel to get IPCHAINS.  2.2.14 should be sufficient,
and comes with the current RH release, and probably most other
distros (not that I keep track of such things).  Be

> I'll save everyone the trouble of asking - I'll document my trials and
> tribulations and write something up for either my web site or another news
> site and let you know when its online.

Good luck,

Archer Sully

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