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Webcast-Catalyst9k
New Member

Traffic to SMTP servers somehow being blocked

This is a tricky situation, so bear with me as I try to explain it. I have a server on my network that needs to communicate with 4 servers on another network via frame-relay. So my server 192.168.2.226 needs to communicate with the following servers on the other end of the frame connection

167.127.14.77

167.127.14.92

167.127.15.41

167.127.15.42

The frame-relay IP addresses are the following.

My end- 172.25.66.246

Other end- 172.25.66.245

So I set up static routes in my router the following way

ip route 167.127.14.77 255.255.255.255 172.25.66.245

ip route 167.127.14.92 255.255.255.255 172.25.66.245

ip route 167.127.15.41 255.255.255.255 172.25.66.245

ip route 167.127.15.42 255.255.255.255 172.25.66.245

Here is where it gets ugly. With those routes added, SMTP traffic from my company to the company on the other end does not go through, it gets stuck in our Exchange que with a "destination unreachable" error. The SMTP servers of the other company IP address are as follows.

167.127.14.74

167.127.14.134

Here is what I have been able to figure out so far with traceroutes about what is happening. Without those routes added, a traceroute shows traffic going to their SMTP servers via my internet connection. With those routes added, traffic to their SMTP servers is trying to go out my frame-relay connection. It sounds impossible but that is what happens. What am I doing wrong? I can provide the config for my frame-relay router, PIX and internet router if need be. I am fairly new to this stuff, so it may be something really simple that I am missing. Thanks!

5 REPLIES
New Member

Re: Traffic to SMTP servers somehow being blocked

Is it just SMTP??? Can you open any TCP connections to the servers.. Try and telnet (on port 25) from the exchange server that has the stuck mail to the other mail servers and see if you get a connection first of all

Travers

New Member

Re: Traffic to SMTP servers somehow being blocked

Take a look at the following in your router:

1) In the router you added the static routes, check the route to address 167.127.14.74 (show ip route 167.127.14.74). Is the route via you FR connection or the Internet?

2) What routing protocols are you running on this router (show ip protocols)?

3) Is ip classless turned on ('ip classless' statement in the config - usually after the routing protocol configuration)?

If you would like to provide this information it may be helpful.

Greg Stevens

New Member

Re: Traffic to SMTP servers somehow being blocked

Thanks for the reply, here are the answers.

1. % Network not in table

2. EIGRP

3. IP classless is not turned on.

New Member

Re: Traffic to SMTP servers somehow being blocked

You will need to turn on IP CLASSLESS (global config command 'IP CLASSLESS'). This should solve your problem. The default behavior was changed from disabled to enabled in IOS version 11.3.

When a router, without IP CLASSLESS enabled, receives a packet destined for a subnetwork it will look up the route in it's table. If there is no route, it looks for a route to the "classful" network address. If there is no route to the clasful network address the router drops the packet.

If IP CLASSLESS is enabled, when the router does not have a route to the subnet it will forward the packet to the best matched supernet (normally the default gatewaty - 0.0.0.0).

I hope this helps you out.

Greg Stevens

New Member

Re: Traffic to SMTP servers somehow being blocked

I hope I'm not missing something here. What I see is that you have added routes to the following hosts:

167.127.14.77

167.127.14.92

167.127.15.41

167.127.15.42

But you are trying to reach the hosts:

167.127.14.74

167.127.14.134

niether of which is referenced in your earlier routes. Then later, you state that a traceroute to the two "missing" hosts shows %network not in table.

Based on the information you've given, it looks to me that the network ISN'T in the table, unless you have some other route defined that would encompass these two hosts. Again, I hope I'm not missing anything, but I think you just need to add a route to the two hosts, or to the subnets on which the hosts reside.

Hope I have helped.

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