ISDN backup and NAT translation table

dmanzetti · ‎04-03-2007

Hello,

I've an issue with the nat translation table when the main adsl connectivity goes down and the isdn backup starts.

I see that the nat table is not automatically cleared when the dialer starts and the clients continue to match the old wrong nat translation.

There is a way to avoid this behaviour?

Thanks in advance

Daniele

Pari Thiagasundaram · ‎04-03-2007

If you are sure its a NAT translation aging issue, can you try

ip nat translation timeout

More info at :

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a0080091cb9.shtml

dmanzetti · ‎04-04-2007

Thank you for the hint.

In my scenario I have some SIP Ip phones that require to signalling with a sip proxy outside the wan.

When the adsl connection goes down and the ISDN backup starts, the phones continue to send their SIP packets (sip register packets every 60 secs)soutside the wan so they continue to match the old nat table and every time it happen the counter starts again and the rule don't expire.

Using shorter nat timeout (ie 10 secs), could it affect the performance of the router?

Thanks

Daniele

NAT

IVAN PEPELNJAK · ‎04-04-2007

You need to set up your NAT so that it generates extended entries (with a route-map). See http://www.nil.com/ipcorner/SmallSiteMultiHoming/ for more details.