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Can I redirect SMTP packets to only ONE machine on our network?

We just have a switched network right now, that breaks up the IT dept from the rest of the building, and the rest of the building is subdivided into 2 collision domains itself. There's about 40 max machines here running WinNT. We recently had a virus infestation and took us about 3 days to remove it. My boss came to me asking about routers and how they might help us out.

I'm CCNA working on CCNP but I don't have any actual hands-on on the job experience with routers. I know I could configure one and the like, but what I'm unsure about is its application to our situation. The virus propogated through email of course, and I mentioned a possibility (though I left it open and told him I would need to review this matter further) of an extended access list that would route the SMTP packets to one particular machine, an RS 6000 running UNIX that we have here, which would have on it some comprehensive virus software, scan the emails, then also act as the mail server and deliver the messages to the individual computers.

Is this possible? I wasn't sure if routers had the capability of routing specifically email packets to a certain machine and preventing any other machines from receiving the packets. We have just a fast cable modem connection right now and the email is sent to a web server that is also acting as the email server.

I'm not sure if this situation sounds too vague, but I do need some advice on whether or not the purchase of a few routers would be cost effective in preventing the routing of email traffic.


Re: Can I redirect SMTP packets to only ONE machine on our netwo

Hi, what you are asking is possible by using access-list, my question to you is - have you considered using PIX firewall?

Let us know if you need further help... Jay

Community Member

Re: Can I redirect SMTP packets to only ONE machine on our netwo

I havn't but would like to know more. How would the PIX firewall specifically aid in our email dilemma as talked about in my previous post?

Cisco Employee

Re: Can I redirect SMTP packets to only ONE machine on our netwo

A PIX firewall won't really help, other than to redirect the SMTP traffic to your internal SMTP server for the virus checking to take place. This is in effect no different to what the router can do.

Also, having the router route SMTP packets to a particular internal address requires port mapping, not just an ACL like the previous person said. You have to set up a static port translation entry, so that traffic coming in on one address on port 25 is mapped internally to another address on port 25.

See the "ip nat" statements here

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