[c-nsp] hsrp with static and dynamic nat for the same outside ip addr and nat timeouts

Daniel Staněk dan at orb.cz
Sat Dec 20 14:59:30 EST 2008

Hi friends,

is it ok to have HSRP NAT configuration like this?

ip nat Stateful id 1
     redundancy dmz
         mapping-id 1
         interface  Vlan2
         protocol   udp
ip nat pool outside-dynamic a.a.a.a a.a.a.a netmask
ip nat inside source route-map nat-fast00 pool outside-dynamic 
mapping-id 1 overload
ip nat inside source static tcp 25 a.a.a.a 25 redundancy 
dmz extendable

The idea is to have two 2811's with HSRP configured at the inside 
interface and doing both static tcp and dynamic overload NAT transtation 
using the same outside ip address.

It seems to be functional but with one small problem - the nat 
translation table of the active router is full of timing-out tcp 
sessions to port 25 (the static nat entry child). The only way how to 
reduce is reduce the nat tcp timeout value, otherewise there are 
thousands of active translations even if the tcp connection has finished 
(with default timeout one day).

Do you think it is a IOS bug or a design error?

Thanks for any advice
Dan Stanek

More information about the cisco-nsp mailing list