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Old 04-24-2008, 09:27 PM
Patricia Bittencourt
 
Default DNS problem (on NAT configuration)

** 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
-A POSTROUTING -o eth1 -j MASQUERADE
COMMIT
*
******** Please, any advice here would be appreciated.

Thanks,
Patricia
********





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Old 04-24-2008, 09:56 PM
Les Mikesell
 
Default DNS problem (on NAT configuration)

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
-A POSTROUTING -o eth1 -j MASQUERADE
COMMIT

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@gmail.com
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
 
Old 04-25-2008, 12:54 PM
John
 
Default DNS problem (on NAT configuration)

On Thu, 2008-04-24 at 14:27 -0700, 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
> -A POSTROUTING -o eth1 -j MASQUERADE
> COMMIT
>
> Please, any advice here would be appreciated.
>
> What's in you /etc/hosts files? You need ip's and names in there for
> clients on the Lan. You will need a primary and secondary dns
> addresses in /etc/resolve.conf
>
>
> Thanks,
> Patricia
>
>
>
>
>
> __________________________________________________ ____________________
> Abra sua conta no Yahoo! Mail, o único sem limite de espaço para
> armazenamento!
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
--
~/john

OpenPGP Sig:BA91F079

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Old 04-28-2008, 04:06 PM
Patricia Bittencourt
 
Default DNS problem (on NAT configuration)

Thank you Les, John, for the reply.
One thing that I noticed is that there are lots of nfs connections in TIME_WAIT. And since I have been facing problems with NFS (ie. taking too much time to cd to a mounting area on client) the problems regarding network appeared.

The TIME_WAIT connections does not free memory, rigth? Do you believe that NFS might be creating a network congestion? Among NFS optimization possibilities is that one in particular that take more effect to avoid performance problems in your oppinion?

Thanks,
Patricia*

--- Em qui, 24/4/08, Les Mikesell <lesmikesell@gmail.com> escreveu:
De: Les Mikesell <lesmikesell@gmail.com>
Assunto: Re: [CentOS] DNS problem (on NAT configuration)
Para:
"CentOS mailing list" <centos@centos.org>
Cc: npaci-rocks-discussion@sdsc.edu
Data: Quinta-feira, 24 de Abril de 2008, 18:56

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
> -A POSTROUTING -o eth1 -j MASQUERADE
> COMMIT
>
> 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@gmail.com
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos



Abra sua conta no Yahoo! Mail, o único sem limite de espaço para armazenamento!

_______________________________________________
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http://lists.centos.org/mailman/listinfo/centos
 
Old 04-28-2008, 04:40 PM
Les Mikesell
 
Default DNS problem (on NAT configuration)

Patricia Bittencourt wrote:


Thank you Les, John, for the reply.
One thing that I noticed is that there are lots of nfs connections in
TIME_WAIT. And since I have been facing problems with NFS (ie. taking
too much time to cd to a mounting area on client) the problems regarding
network appeared.


The TIME_WAIT connections does not free memory, rigth? Do you believe
that NFS might be creating a network congestion? Among NFS optimization
possibilities is that one in particular that take more effect to avoid
performance problems in your oppinion?


TIME_WAIT states happen when you close a TCP connection which shouldn't
happen at all on nailed-up mounts. Do you have the automounter set up
for short timeouts and something that could be traversing the mount
points frequently to stir up traffic and connections? You could switch
to UDP to avoid the TCP state handshakes and overhead.


--
Les Mikesell
lesmikesell@gmail.com

_______________________________________________
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