Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

NAT Invalid Key Lengths Message

Getting the NAT: % Invalid Key lengths for tree insertion message on (5) 2800 routers in different locations running IOS 124.  It is not impacting production. Checked and did not come up with anything. Does anyone have any feedback/info regarding this message? Many thanks in advance.

Cisco Employee

Re: NAT Invalid Key Lengths Message


I did some search, looks like this error message is generated when a code check during a key length calculation in NAT code. If the value returned is "0" then the error message is generated.

For example, and from what I saw this can often happen when we process a wrong packet with ip, that could be caused by a buggy packet sent to the router, or because of a bug on the router.

You can double check this by doing a "debug ip nat detail" and see what NAT was doing just before the error message, however this is a very chatty debug and you need to be cautious if you are going to try that in production.

If the error message occurs very often, I guess it's worth to already try to put a deny in the acl attached to NAT and see if that stops. If not, then you probably need to go for controlled debugging session to find the guilty packets.



CreatePlease login to create content