Isolate Cisco 1841 router fast ethernet port

February 4, 2011 at 19:26:24
Specs: Windows 7
I have a Cisco 1841 router with the following

Serial T1 connection
Fastethernet 1 with network address 192.168.0.1
Fastethernet 2 with network address 198.168.0.1

I want to isolate Fastethernet 2 so that it cannot access the internet or the 192.168.0.1 network. Only incoming request is available.

thank you


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#1
February 5, 2011 at 05:36:00
To separate it from the other subnet you'll have to change one of the two interfaces to a different subnet because at present you show them as being in the same subnet.

How does that interface access the internet now?

Without knowing that, there's no way to tell you how to stop it from doing so.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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#2
February 6, 2011 at 18:41:39
The interfaces are in different subnet, 198 and 192. I have an IP route 0.0.0.0 0.0.0.0 to the T1 serial interface.

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#3
February 7, 2011 at 10:28:41
My bad, I didn't notice one was 192 and the other 198.

They shouldn't be able to communicate at all by default. You would have to actually set a route between in order for them to communicate with each other. Check for a route and delete it if you find one.

If you don't mind, post the subnet mask for both subnets too.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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Related Solutions

#4
February 12, 2011 at 16:26:14
Correct me if I'm wrong, since both fastethernet port are connected on the Cisco 1841 router that's why it knows how to route the traffic between 198.168.0.x to 192.168.0.x and vice versa. From what I read, it seems like the only way to block the traffic is through Access List?

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#5
February 14, 2011 at 07:45:07
While I haven't done a lot of work with Cisco routers (we use OpenBSD based routers where I work) I do have a fair bit of experience with Cisco switches and the Cisco IOS. It's been my experience they don't make routes between subnets and interfaces by default. Which is to say, you have to manually create routes yourself.

You could check the routing table for the existence of routes between subnets. If they are there, delete them. However, I suspect you won't find any there unless you, or someone else in your IT department has created them.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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