Need help debugging NFSv3+KRB5+PAT (Port Address Translation) problem

Need help debugging NFSv3+KRB5+PAT (Port Address Translation) problem

[Joschi Brauchle]

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Hello everyone,

I need some help debugging a NFSv3 + KRB5 + PAT (Port Address 
Translation) problem.

We have two hosts behind a firewall and an NFSv3 server outside 
requiring KRB5 authentication.

1) Client_NAT is using NAT (network address translation),
2) Client_PAT is using PAT (port address translation)
to reach the NFSv3 server through the firewall.

Both clients are configured identically in terms of Kerberos and so on.

Mounting an NFSv3 share now fails on Client_PAT with the message:
RPC: server SERVERNAME requires stronger authentication.
On Client_NAT, mounting succeeds.

We strongly suspect the port address translation to be the reason for 
the failure, but would need help confirming this and advice on how to 
fix it.

Please find here the RPC debug logs from
Client_NAT: http://pastebin.com/9RANqVgY
Client_PAT: http://pastebin.com/TiscNVqW
Here is a DIFF between the two: http://pastebin.com/wCg7WyYd

I'm grateful for any help on this problem!

Best regards,
Joschi Brauchle
-- 
Dipl.-Ing. Joschi Brauchle, M.S.

Institute for Communications Engineering (LNT)
Technische Universitaet Muenchen (TUM)
80290 Munich, Germany

Tel (work): +49 89 289-23474
Fax (work): +49 89 289-23490
E-mail: joschi.brauchle@tum.de
Web: http://www.lnt.ei.tum.de/


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Re: Need help debugging NFSv3+KRB5+PAT (Port Address Translation) problem

[Jeff Layton]

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On Fri, 26 Sep 2014 17:31:55 +0200
Joschi Brauchle <joschi.brauchle@tum.de> wrote:

> Hello everyone,
> 
> I need some help debugging a NFSv3 + KRB5 + PAT (Port Address 
> Translation) problem.
> 
> We have two hosts behind a firewall and an NFSv3 server outside 
> requiring KRB5 authentication.
> 
> 1) Client_NAT is using NAT (network address translation),
> 2) Client_PAT is using PAT (port address translation)
> to reach the NFSv3 server through the firewall.
> 
> Both clients are configured identically in terms of Kerberos and so on.
> 
> Mounting an NFSv3 share now fails on Client_PAT with the message:
> RPC: server SERVERNAME requires stronger authentication.
> On Client_NAT, mounting succeeds.
> 
> We strongly suspect the port address translation to be the reason for 
> the failure, but would need help confirming this and advice on how to 
> fix it.
> 
> Please find here the RPC debug logs from
> Client_NAT: http://pastebin.com/9RANqVgY
> Client_PAT: http://pastebin.com/TiscNVqW
> Here is a DIFF between the two: http://pastebin.com/wCg7WyYd
> 
> I'm grateful for any help on this problem!
> 
> Best regards,
> Joschi Brauchle

I'm not terribly familiar with the PAT vs. NAT distinction, but many
NFS servers require you to use privileged ports to connect to them. Is
your PAT client having its privileged port converted to a
non-privileged one?

If so (and if the server is Linux-based) then you can try to get around
that by exporting with the "insecure" export option.

-- 
Jeff Layton <jlayton@poochiereds.net>

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Re: Need help debugging NFSv3+KRB5+PAT (Port Address Translation) problem

[Joschi Brauchle]

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On 09/26/2014 05:56 PM, Jeff Layton wrote:
> On Fri, 26 Sep 2014 17:31:55 +0200
> Joschi Brauchle <joschi.brauchle@tum.de> wrote:
>
>> Hello everyone,
>>
>> I need some help debugging a NFSv3 + KRB5 + PAT (Port Address
>> Translation) problem.
>>
>> We have two hosts behind a firewall and an NFSv3 server outside
>> requiring KRB5 authentication.
>>
>> 1) Client_NAT is using NAT (network address translation),
>> 2) Client_PAT is using PAT (port address translation)
>> to reach the NFSv3 server through the firewall.
>>
>> Both clients are configured identically in terms of Kerberos and so on.
>>
>> Mounting an NFSv3 share now fails on Client_PAT with the message:
>> RPC: server SERVERNAME requires stronger authentication.
>> On Client_NAT, mounting succeeds.
>>
>> We strongly suspect the port address translation to be the reason for
>> the failure, but would need help confirming this and advice on how to
>> fix it.
>>
>> Please find here the RPC debug logs from
>> Client_NAT: http://pastebin.com/9RANqVgY
>> Client_PAT: http://pastebin.com/TiscNVqW
>> Here is a DIFF between the two: http://pastebin.com/wCg7WyYd
>>
>> I'm grateful for any help on this problem!
>>
>> Best regards,
>> Joschi Brauchle
>
> I'm not terribly familiar with the PAT vs. NAT distinction, but many
> NFS servers require you to use privileged ports to connect to them. Is
> your PAT client having its privileged port converted to a
> non-privileged one?
>
> If so (and if the server is Linux-based) then you can try to get around
> that by exporting with the "insecure" export option.

We do not have control over the NFS server, but from the firewall logs I 
can see that the PAT client trying to access the server with an 
originally privileged port (<1024) gets translated to a non-privileged 
one. Shortly after that, the mount fails.

So I guess this is the problem! Thanks for the hint.


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