Mail server looses Internet access intermitently

[grimard_cisco]

Hi,

We access the Internet through a 1841 router using NAT on a 3Mbits DSL line.

Behind this router we have a mail/DNS server.

Intermitently, this server looses Internet access. No web browsing, no DNS lookup, no telnet on outside (Internet) hosts. At the same time, this server can access internal computers. At the same time, all other machines on the internal network and on same subnet can access the Internet.

I am pretty sure that this is a problem with the 1841 router because if I RELOAD the router the server can access all Internet resources again.

If I don't reload the router and just wait, Internet connectivity resumes after some time (between 15 minutes and 2 hours).

Any ideas ?

Thank you.

[nethelper]

Hello,

how is your NAT set up ? Can you post the configuration of your router ? Check for the number of NAT translations, which might be too high (show ip nat translations). Can you also post the output of 'show version' ? This might be an IOS bug as well, one never knows...

Regards,

Nethelper

[grimard_cisco]

I've attached my router configuration (xxx.xxx.xxx.xxx is the public IP address) and the output of "show version".

"show ip nat translations" gives me 243 lines. Is it to high ?

Thank you.

[nethelper]

Hello,

the config looks ok, and 243 translations doesn't sound abnormally high. One thing I noticed in your configuration is that the speed and duplex settings on your interfaces are set to auto, can you set them to fixed (e.g. 100/Full) on the router, as well as on the devices connected to those interfaces ?

Regards,

Nethelper

[grimard_cisco]

Anything else ?

[lgijssel]

It might be an issue with the ip pool that you assigned for Internet browsing. The most common used config uses overloading on the interface-ip of the Internet connection. What you do is not wrong but a bit special and it might expose a bug that will not run into otherwise.

You could try to change it, and if it helps perhaps you know where to search.

Regards,

Leo

[grimard_cisco]

Which command in the config do you refer to ? And how do you suggest I change it ?

[lgijssel · Accepted solution]

ip nat inside source list 100 pool internet overload

should be changed to:

ip nat inside source list 100 interface FastEthernet0/1 overload

You may then delete the pool if you like.

Regards,

Leo

[grimard_cisco]

I made the change, I'll post the results here.

Thank you.

[grimard_cisco]

The problem did not happen since I've made this modification, so this issue seems solved.

Thank you.