[wellylug] saturn cable connection with linux

[Steve Withers]

Don Jones wrote:

>Hmmm
>
>Im getting a saturn cable modem installed on Friday
>
>>You plug your ethernet card into the cable modem 
>>
>using the ethernet 
>
>>cable they provide.
>>
>
>Is this a X-over do you know?
>
I think so.....

>>Saturn give you an IP address, a netmask, a 
>>
>gateway address and two dns 
>
>>servers. 
>>
>
>Whats the netmask?
>
255.255.255.0

>
>The description suggests that the saturn cable 
>"modem" is just a bridge/media converter/layer2 
>device. Has anyone investigated this? Essentially 
>the whole cable network is one big LAN. This 
>suggests that anyone who plugs the "modem" strait 
>into a hub with a number of hosts on it is 
>essentialy an extension of the lan. Except with a 
>bridge in between. So presumably it filters 
>incomming frames at the "modem" based on its 
>external MAC address. That will allow filtering of 
>inbound frames (ie you wont be able to sniff traffic 
>on the main LAN beyond the bridge). But what about 
>frames comming from internal hosts in the hubbed 
>setup described above, how does the bridge decide 
>which frames to forward? Either it forwards then all 
>and you have internal addresses out on the main 
>segment or does it do some kind of arp or deny any 
>ip addresses in the internal range? - whatever - 
>either would bump it up to a layer 3 device - anyone 
>know?? 
>
I tried plugging it into a hub and a switch. It doesn't work...My 
Theory: because the hub isn't intelligent enough to have an IP address 
to match its mac address...... Whatever....it didn't work no matter hwat 
I tried. 

So I have a linux PC with two network cards. One is plagged into the 
cable modem and uses the provided IP address. The other is plugged into 
the hub and has the network addresing scheme I use on my LAN (10.*.*.*). 
I recommend using a 100MB card for the inside lan and and a 10MB card 
for the connect to the cable modem.
Main idea here is to have two different NICs. I have never been able to 
get two identical NICs going in the same PC. I think the dirvers get 
confused or something. But if I use two different NICs, it works first 
time, every time.

Windows 98SE had the same issue with identical NICs last time I tried 
it. Either a driver limitation or a Windows limitation. 

I then set up MASQ and IPCHAINs on my RH 7.0 system. Eventually, I'll 
move it to RH 7.2 and use IP filter instead (the new firewall).....but I 
wanted the documentation to improve a bit before I attempt it. It was 
pretty good about 6 months ago....now I just need to find the time to do 
the change. It will take most of a day to back up all the custom config 
files I have and then get them all going again on the new build. That's 
why I keep putting it off.

I've been running this way for over 2 years now.....and have re-booted 
my Linux firewall 6 times in that period.....if you disregard the 
re-built that took me from RH 6.2 to RH 7.0.

Steve 



 



 


 


>
>
>I wonder what the specs of the segment are - is it 
>real ethernet (anyone know what type?) - 100Mbps or 
>Gigabit (its probably 1544Mbps or something)? Could 
>you hack together a connector to bypass the modem - 
>like a bnc 10base2 card running at whatever the 
>segments speed is? or some type of coax to cat5 
>media convertor running at the right speeds.
>
>Forgive my ramblings - but Im curious ;)
>
>Don Jones
>



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