Am I being stupid (netmask question)

Hodders · 30 Aug 2007 at 10:41

Trying to connect a simple netgear router to a leased line terminated with a cisco bridge.

The information we have w.r.t. the network settings are:

Network range: 81.195.82.12/30 first two addresses have been assigned gateway and cisco router. Useable address starts at .14

My settings for the WAN side of the netgear router:

IP address: 81.195.82.14
Netmask: 255.255.255.252 (where 252 = 11111100)
Gateway: 81.195.82.12

The problem is that the netgear router page won;t accept the netmask as it is complaining about it being invalid. It will accept 255.255.255.0.

My understanding of this is that the netgear will believe that the whole subnet 81.195.82.x will be accessible via it's lan port rather than having to go our via the gateway.

The problem is that the netgear can't even ping the gateway or cisco router address. A laptop attached to the lan side of the netgear router can ping the Wan side of the netgear router.

All was working fine with an old smoothwall router (that has died - hence the need for a replacement).

Any ideas ? Is the 255.255.255.0 netmask the cause of this ?

TheKnat · 30 Aug 2007 at 10:56

Although its not ideal, using 255.255.255.0 shouldn't be a problem unless you are trying to go to addresses on the the 81.195.92.X range that aren't in your WAN.

As long as the netgear has the correct default gateway then, if you go to www.bbc.co.uk it should go to 215.58.251.202, which is outside the WAN range and should therefore go through your gateway.

Rather than performing pings, its probably more useful to do a trace router (tracert command in Windows) to find out where the problem is happening.

Hodders · 30 Aug 2007 at 11:02

I have been pinging up the chain:

Laptop to Lan on netgear - OK
Laptop to wan on netgear - OK
Laptop to gateway on cisco - Fail
Laptop to cisco IP address - Fail
Laptop to known IP address on internet - Fail

I'm going to try with a different piece of equipment and see how that gets on.

oddjob62 · 30 Aug 2007 at 11:09

Have you tried letting the router pick up an IP automatically and seeing what happens?

Tui · 30 Aug 2007 at 11:50

Is 81.195.82.12/30 correct? That's definitely a 255.255.255.252 netmask but the only usable addresses are .13 and .14, .12 being the network and .15 the broadcast.

Hodders · 31 Aug 2007 at 13:23

In the end it was email from the leased line people. The netmask was right (it was just the silly netgear router not accpeting it). The gotha was that the leased line email said the .12 was the gateway and .13 was the cisco router. In the end it was the other way round !

All working now.