[c-nsp] NAT issues.

[Andriy A. Yerofyeyev]

Hi all!

We have 2611 router with interfaces :

Interface                  IP-Address      OK? Method 
Status                Protocol
Ethernet0/0                unassigned      YES NVRAM  
up                    up
Ethernet0/1                172.16.1.1      YES NVRAM  
up                    up
Serial0/1                  213.130.0.1     YES TFTP   
up                    up
Virtual-Access1            unassigned      YES unset  
up                    up
Dialer1                    213.130.5.1     YES IPCP   
up                    up

Dialer0(Ethernet0/0 , Virtual-Access1) used primary for failower. Main 
link is Serial0/1.
Nat inside interface Ethernet 0/1, nat outside interfaces Serial 0/1 and 
Dialer1.

ip route 0.0.0.0 0.0.0.0 Serial0/1       name main
ip route 0.0.0.0 0.0.0.0 Dialer1     200 name failower

So , if our T1(Serial0/1) goes down all traffic is rerouted to the PPPOE 
interface (Dialer0).
When T1 goes up again all *new* traffic goes through Serial0/1 *except* 
active sessions for which
exist nat translations to Dialer0.

For example control traffic from SCCP phones goes thru Dialer0 and RTP 
traffic from same phone
(as new session) goes thru T1 line,as result we have one-way or (more 
often) no-way audio.

Setting net timeout to lower value (10-30 sec) did not help because of 
low keepalive interval on SCCP
phones and possibility to disrupt communications between phone and softPBX.

Can you give us some advices how to avoid this situaton ?