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New Member

IPv4 NATs not working

I've been struggling for this one now for about 3 weeks.

We have a router that boarders a B2B connection and within the config we NAT our internals to a specific set of addresses.

So, for example (addresses have been changed from production):

ip nat inside source static

ip nat inside source static

ip nat inside source static

ip nat inside source static

ip nat inside source static <--- Problem child


ip nat translation timeout 300

What I am running into is the inside local (aka Real) is a DNS server that forwards requests to another DNS server across our B2B connection.  Every-so-often, the router decides to stop translating the address and nobody can access certain hosts. I have to issue 'clear ip nat translation *' to get it working aging.

2811 Running 12.4(24)T3


Everyone's tags (7)
New Member

Re: IPv4 NATs not working

Did you check the cpu and memory utilization before clearing the nat translation?

Sent from Cisco Technical Support iPad App

New Member

IPv4 NATs not working

Yep, It's snoozing

IPv4 NATs not working

For what its worth my strange NAT problems have always be resolved with an IOS change.


New Member

IPv4 NATs not working

Yeah, I'm thinking about jumping up to T5 on the current train.  I've also had it freak out when using object-groups in ACLs

New Member

IPv4 NATs not working


how much dram and flash do you have for that router?

i was reading release note here

it seems that those T releases do have problems with nat

well, perhaps T5 is a good start, but im suggesting you start with T7, it resolve quite important bug:


Symptoms: A memory leak is seen when NAT is configured.

Conditions: This symptom is observed when NAT is configured.

Workaround: There is no workaround.


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