[c-nsp] Strange corrupt DNS Cache in IOS

[Javier Henderson (javier)]

> On Aug 15, 2014, at 3:55 AM, Sascha E. Pollok <sp at iphh.net> wrote:
> 
> Hello networking fellows!
> 
> We are trying to find the cause of a corrupt local DNS cache of a Cisco 1803 running 15.1(4)M8 (also appeared on 12.4something - 15.1 ist just a desperate attempt of solving).
> 
> The router acts as a local DNS resolver for locally connected clients using "ip dns server".
> 
> Every now and then it seems to break locally cached IPv4 A-RRs like this:
> 
> Router#show hosts
> test.fqdn.fqdn           None  (temp, OK)  0   IP    0.0.0.5  <---
> 
> This seems to happen for hosts that also have an AAAA RR. To us it looks like it mixes AAAA and A records as the IPv6 address for this host is [...]::5. This happens with other hosts too.
> 
> The host is sometimes first seen correctly with an "IP" and "IPv6" entry in the cache but then changes to the broken "IP" RR while sometimes even keeping the correct IPv6 entry. It never happens to the IPv6 address.
> 
> Debugging "debugging domain" and "debugging domain replies" didnt give a clue.

Sascha,

This looks like the symptoms of bug CSCub00466, where IPv4 entries are corrupt when an IPv6 PTR query takes place.

Can you please open a case with us (Cisco TAC) so we can track this down?

Javier Henderson
javier at cisco.com