Telwest - two routers on one BB connection

[zebulebu]

Hope someone on here can let me know if what i want to do is:

a: possible, and

b: permitted by Smellywest

I have their 4Mb service and am happy with it (apart from a little hiccup last year which was fixed by switching me to a different upstream after three weeks of hell!)

What i want to do is connect two routers downstream from the cable modem (Surfboard SB4200) via a hub. This might seem a bit odd, but basically I want to take a peek around at the traffic outside my firewall (i.e. traffic that is hitting my modem but not making it through the NAT firewall I have installed). I'd like to be able to do this with little disruption to my network, and no danger to my 'real' LAN.

I've stuck the cable from the modem into a hub and connected another cable from the hub back to the router's WAN port, then sniffed the traffic from another port on the hub via a dedicated linux box and it works fine - I get to see all the stupid little net send spams and usual background noise like scans for SQL Servers on 1433/143, VNC boxes on 5900 & Dameware on 6139. However, for security reasons i don't want to leave it like this for any more than about ten minutes (I'm proud of never having been hacked yet and would like to keep it that way for as long as possible )

Does anybody know whether I can set this up? Maybe using the cable modem's IP as the gateway for each router?

Just in case anyone's wondering, its for a presentation on port scanning I'm giving at work!

Thanks in advance (apologies to anyone on here who reads on the Scream forum - I'm going to post this there too)

[Jon T]

Your not going to get very far doing this at all, reason being is that your modem will only give out one WAN IP address(this is a completely different thing to the your Telewest gateway IP).

[zebulebu]

Cheers Jon

I kind of figured that there would only be one WAN IP handed out by the modem - but can I not segregate the traffic downstream by routing it through a hub first before it hits two routers?

Something like:

.................................................. ........ -- Router 1 -- LAN
Internet -- WAN IP -- Modem -- Hub ---
.................................................. ........ -- Router 2 -- Secondary LAN


(please excuse the crappy ASCII art)

That would be like sticking a sniffer 'outside' the firewall without endangering the 'real' LAN, would it not?

Cheers for taking the time to reply!

[Stuart C]

Originally Posted by zebulebu

Cheers Jon

I kind of figured that there would only be one WAN IP handed out by the modem - but can I not segregate the traffic downstream by routing it through a hub first before it hits two routers?

Something like:

--- Router 1 --- LAN
Internet --- WAN IP --- Modem --- Hub ---
--- Router 2 --- Secondary LAN


(please excuse the crappy ASCII art)

That would be like sticking a sniffer 'outside' the firewall without endangering the 'real' LAN, would it not?

Cheers for taking the time to reply!

You would need a second IP for both routers to have Internet access. Telewest/NTL only issue one IP for each modem.

[exC&W]

could you not get the desired effect by the following

.................................................. ............ -wired- PC1
Internet -- WAN IP -- Modem -wired- Router 1 -wired- Router 2 -wireless- PC2

[kfridge]

why not set up a smoothwall hardware firewall with red, orange, and green interface (you need only a basic machine with 3 NIC's to do this)

the red interface is connected to your cable modem, the green interface to your internal LAN, the orange is a DMZ to which you can connect a machine to do your packet sniffing etc.

all machines connected to the DMZ (orange network) cannot get to the green network unless pinholes are opened on the firewall.

think this would be a better solution than multiple routers etc?

more details on smoothwall are at www.smoothwall.org