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Old 06-12-2006, 06:06 AM   #1
Mq2004
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Mail problem through WiFi Bridge that works perfectly for all other protocols


I'm using a Belkin F5D7330uk "802.11g Wireless Ethernet Adapter" to connect my WiFi enabled laptop to the otherwise wired home network. This is built round a Smoothwall (express 2.0) firewall, providing services such as DHCP, DNS cache, transparent web proxy etc. I've been using the smoothie for several years and really pleased with it BTW.

The 7330 is set to AdHoc mode and receives basic configuration (netmask, private ip address, gateway) from DHCP, these appear correct and I can see no other settings available apart from channel, encryption etc.

The laptop wireless card has a static IP address in the same sub-net (though outside the band allocated to DHCP) and the default route is the smoothie box. It's an HP Pavilion zv5000 running OpenSuSE 10.1 (kernel 2.5.13) and the local firewall is active with only SSH enabled. Also tried disabling local firewall, no effect on the problem.

Web browsing (firefox or konqueror) works perfectly on the laptop, as does NFS file sharing, CUPS printer access - even realplayer streaming audio and video are just perfect. However POP3 email receipt and SMTP mail sending are broken - conenction simply times out. I'm using Thunderbird, up-to-date version from the distro. Same version on a - wired - desktop machine works perfectly.

The web proxy log on smoothie shows the laptop's static address for the browser activity, indicating that (at least for this connection) the bridge is simply forwarding the packets transaparently, as desired. I can see no firewall (or proxy) logs pertinent to the mail problem.


Apart from trying to analyse packets on the line with ethereal - my reluctant next step - can anyone please suggest why email is broken when routed through the WiFi bridge?
 
Old 06-13-2006, 08:19 AM   #2
Hangdog42
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To be honest, my first suspect would be Thunderbird. I'd go through the various configurations with a fine-tooth comb and make sure all settings (servers, users, passwords) are correct. If you can, I'd test it either on another network or from in front of the Smoothwall box.
 
Old 06-13-2006, 09:07 AM   #3
Mq2004
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Hmm, I suspected thunderbird too, so I copied the ~/.thunderbird from the desktop machine (in fact both are now pointers to an NFS share). I can't see it making a difference, but both installations use the same "Local Folders" directory as well, also via NFS (and therefore share the lock file!). No change. The only difference is the presence of the WiFi bridge in the laptop's network connection.

So next I wound up ethereal, though I'm far from expert with it. I'd like to filter out the NFS, CUPS etc. stuff but can't see how to, what I can see is that TB asks DNS for the IP of the mail server, gets it (from Smoothie) then sends a TCP request to it. There's no reply to this - hence no mail.

I need next to sniff on the other side of the bridge, as I don't know which of these points it's getting to:

1. the packet fails to reach the firewall (due to some config issue in the WiFi bridge)
2. the packet reaches the firewall, but is dropped (can't see any sign in the FW logs)
3. the packet gets out to the mail server but the reply is dropped (again, nothing in FW logs)
4. the reply is routed to the bridge where it's lost

So I'm making progress, but very slowly. We're in a heatwave here in southern England, it reached 33' in my office yesterday and the cupboard where the server and firewall live was even hotter (air con is pretty rare here!). This isn't helping! I do have an old hub and spare PC which I can use as a sniffer though.

Thanks for the suggestion anyway, any more ideas please !?
 
Old 06-14-2006, 08:19 AM   #4
Hangdog42
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Quote:
I can see is that TB asks DNS for the IP of the mail server, gets it (from Smoothie) then sends a TCP request to it. There's no reply to this - hence no mail.
That's some nice work so far. And I think it clears TB of suspicion of wrongdoing. I also agree that the next logical step is to sniff the other side of Smoothwall and see if TB packets are getting past it.


Quote:
The 7330 is set to AdHoc mode
Sorry I missed this from your first post, but are you sure this is running in AdHoc mode? Usually you use Managed or Auto for a network set-up like yours. If you are in AdHoc try the other two and see if it makes a difference.


The only other thing I can think of is to connect the laptop via CAT5 and see if that works. If you use the same static IP and settings on a wired connection and it works, that suggests that the wireless config is the problem. If it doesn't work, it points to Smoothwall as the culprit.

Quote:
it reached 33' in my office yesterday
Ouch! With temperatures like that I bet your system is just staging a work slow-down trying to keep cool.
 
Old 06-19-2006, 03:56 PM   #5
Mq2004
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Hi again, It's finally cooled down a bit and I managed to resurrect an old PC to use as a sniffer. It seems that my suspicion above was correct - the Belkin F5D7330uk isn't forwarding the POP3 request to the ISP.

The big question is how to get around this - I'm stumped. I'll ask in a few other fora now I have a better handle on the problem (and will report back here if and when I solve it!)

Cheers
Richard
 
Old 06-19-2006, 05:37 PM   #6
Hangdog42
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Since the Belkin device works for other forms of communications, I think the driver can be ruled out. In fact the only thing that makes any sense to me would be a firewall rule that is dropping packets. Do you have a firewall on this machine?
 
Old 08-14-2006, 03:22 PM   #7
Mq2004
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Finally gave up on the belkin and bought a sitecom wireless router which I'm using with the dsl port & dhcp server switched off. It all works perfectly, with no changes to the setup of any of my linux machines.

To help others who may follow:

Belkin F5D7330uk can be used as an access point (that's what it's sold as) but in at least some circumstances it fails to forward some packets, esp. those destined for an external (i.e. outside the subnet mask) POP server.

Thanks to all who helped (i.e. Hangdog42)
--
Cheers
Richard.
 
Old 08-14-2006, 04:53 PM   #8
Hangdog42
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Thanks for posting what you found. It sounds as if that Belkin access point isn't worth anything.
 
  


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