Port forwarding dissapearing from config.

[Brunhuber Adrian]

Hi i have a weird problem at one of my customers. It`s weird but trust me on this.

ip nat inside source static tcp 192.168.1.4 25 x.x.x.x 25 extendable

ip nat inside source static tcp 192.168.1.250 80 x.x.x.x 80 extendable

ip nat inside source static tcp 192.168.1.252 80 x.x.x.x 84 extendable

ip nat inside source static tcp 192.168.1.253 80 x.x.x.x 85 extendable

ip nat inside source static tcp 192.168.1.251 443 x.x.x.x 443 extendable

ip nat inside source static tcp 192.168.1.250 22 x.x.x.x 2222 extendable

ip nat inside source static tcp 192.168.1.252 22 x.x.x.x 2223 extendable

ip nat inside source static tcp 192.168.1.253 22 x.x.x.x 2224 extendable

ip nat inside source static tcp 192.168.1.6 3389 x.x.x.x 3390 extendable

ip nat inside source static tcp 192.168.1.250 5666 x.x.x.x 5666 extendable

After 2-3 days the forwarding statement  "ip nat inside source static tcp 192.168.1.250 80 x.x.x.x 80 extendable " dissapears from the running confing, but the forwarding is working. After the reset the forwarding is missing.  Anybody knows what bug i`m hitting. Thanks.

[Peter Paluch]

Hello Adrian,

Sometimes the most simple reason is the most probable... You said that after the reset, the "forwarding is missing" - I take it that after reloading the device, the offending ip nat inside source static command is not present in the running-config and hence the static port forwarding does not work. That would in turn mean that this command is not present in the stored startup-config file because otherwise, it would be loaded during the device bootup.

Is it absolutely certain that this command is present in the startup-config? Also, is it absolutely certain that there is no one modifying the running-config - via CLI, SNMP, ...?

Best regards,

Peter

[Brunhuber Adrian]

Yes i think this is happening. The ip nat inside static command dissapears from running config , when after configuring some other things from the CLI i issued the wr command the running replaces the startup and at the reboot the forwarding is not there. Nobody have the access but me on the router. When after some time i look at the config the line is gone but when i issue sh ip nat translations it shows the static mapping and everything is working,except the line in the running config. Strange

[Peter Paluch]

Hi Adrian,

A rule of thumb would be to try to upgrade your IOS, just in case this is some weird bug. What IOS version are you running currently?

Best regards,

Peter

[Brunhuber Adrian]

I would update the IOS today for now i`m running :

System image file is "flash0:c1900-universalk9-mz.SPA.151-2.T2.bin"

[Denis Orlov]

Hi. I have the same behavior on Cisco Router 3825.

I'm configure portforwarding using command:

ip nat inside source static tcp x.x.x.x 25 y.y.y.y 25 extendable

After some time period this record dissapear from running-config

WANBorderCisco3825#sh run | incl 25 extendable

WANBorderCisco3825#

And of course portforwarding become unworking after suddenly router reload.

And I need to configure portforwarding again.

Current IOS version - c3825-advipservicesk9-mz.124-15.T7.bin

I try to upgrade IOS and write about results.