Netbios problem with NAT

Netbios problem with NAT

[Song Wang]

Hi,

I found a problem with netbios when 2 Windows PCs behind a NAT router try to 
access
the same shared directory on the Windows server sitting on the other side of 
the NAT router.
(kernel 2.4.17 w/ iptables 1.2.7a)

For example

4.3.2.1--------<NAT router>---------PC1 192.168.1.2
                                       |-------PC2 192.168.1.3

Windows XP PC1 and PC2 got private IP address from the DHCP server on the 
NAT router.
When PC1 alone accesses the shared directory on the Windows XP server (or 
PC) 4.3.2.1 using
\\4.3.2.1, there is no problem. However, when PC2 also accesses the same 
directory via
\\4.3.2.1, problem arises. You can reproduce the problem in this way

Copy a file from \\4.3.2.1 to PC1, when the copying is ongoing, do a refresh 
(F5) or copy a file
on the same \\4.3.2.1 from PC2, you will see a dialog pop up on PC1

"The specified network name is not available"

The copying process got stuck.

Strangely, the problem seems to happen only when the two PC get the IP 
address
via DHCP. If one of the two PCs use the static IP address, the problem seems 
to go away.

Could this be a problem of netbios with connection tracking? Maybe we need 
to write
a nat helper module for netbios?

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Re: Netbios problem with NAT

[Harald Welte]

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On Tue, Jul 22, 2003 at 12:00:25AM -0700, Song Wang wrote:
> Hi,
> 
> I found a problem with netbios when 2 Windows PCs behind a NAT router try 
> to access the same shared directory on the Windows server sitting on
> the other side of the NAT router.  (kernel 2.4.17 w/ iptables 1.2.7a)

why did you ever think that this would work?  Even the microsoft
knowledge base contains an article that you'd need some kind of special
NAT support for it, in order to mangle the contents of the netbios
packets.

> Could this be a problem of netbios with connection tracking? Maybe we need 
> to write a nat helper module for netbios?

yes, indeed. A nat helper would be required.  Patches welcome.

-- 
- Harald Welte <laforge@netfilter.org>             http://www.netfilter.org/
============================================================================
  "Fragmentation is like classful addressing -- an interesting early
   architectural error that shows how much experimentation was going
   on while IP was being designed."                    -- Paul Vixie

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