[CentOS] DNS problem (on NAT configuration)

Thu Apr 24 21:56:37 UTC 2008
Les Mikesell <lesmikesell at gmail.com>

Patricia Bittencourt wrote:
>    Hi,
>         I'm dealing with a problem that the worker nodes that are behind 
> a NAT aren't able to reach outside from time to time. (ie: on a given 
> moment I can ping an address name and immediately after I cannot: "ping: 
> unknown host").
>         The NAT was configurated using the following:
> *nat
>          Please, any advice here would be appreciated.

The obvious fix is to configure your NAT gateway host as a caching DNS 
server and make the hosts behind NAT use it's private address instead of 
something on the other side.  However, it should work anyway.  Do you 
have enough traffic that you could be filling your conntrack tables? UDP 
   entries remain for a timeout interval since you can't see a disconnect.

See if the /proc/sys/net/ipv4/netfilter/ip_conntrack_* values are 
reaonable for your scale.

   Les Mikesell
    lesmikesell at gmail.com