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Posted
27 February 2005

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Nerd Factor X

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3 Comments

Netgear Bugs

Sometimes Google is the best approach to a technical problem, but other times it's best to just dive in with a packet sniffer.

Just recently The SO has been complaining about being unable to print over the wireless network. Plug into the ethernet and printing works just fine. A perplexing dillema.

The printer (Samsung ML-1710, a very nice and cheap laser printer) is hooked up to the FreeBSD server running CUPS. This is in turn connected to a Netgear WGR614 wireless router and 4-port ethernet switch. The printer appears in the OS X Printer list as a "shared printer" without requiring any special configuration. Which is nice, when it works.

What was/is happening is that when switching to the wireless network, the Host column in the Printer Setup Utility changes to 0.0.0.0, and printing is no longer possible.

Opening up the packet sniffer (the one built into Interarchy) and I see what happens in the 'normal' case, when connected to the ethernet network:

UDP packet from 192.168.0.5:ipp(631) to 192.168.0.255:ipp(631) (101 bytes)
IP Header:
 Version: 4; Header Length: 20; TOS: 0; Packet Length: 129
 Identifier: 17132; Fragment Offset: 0
 Time To Live: 64; Protocol: 17; Header Checksum: 46379
UDP Header:
 Packet Length: 109; Checksum: 60424
Data:
1006 3 ipp://0.0.0.0:631/printers/Samsung "" "ML-1710P" "Samsung ML-1710 Foomatic/gdi (recommended)"

UDP packet from 192.168.0.5:ipp(631) to 192.168.0.255:ipp(631) (112 bytes)
IP Header:
 Version: 4; Header Length: 20; TOS: 0; Packet Length: 140
 Identifier: 64710; Fragment Offset: 0
 Time To Live: 64; Protocol: 17; Header Checksum: 64325
UDP Header:
 Packet Length: 120; Checksum: 63549
Data:
1006 3 ipp://lola.geekflash.com:631/printers/Samsung "" "ML-1710P" "Samsung ML-1710 Foomatic/gdi (recommended)"

What each CUPS server does is send out a local broadcast every 30 seconds (by default) advertising the printers that it can serve. I'm still not entirely sure why my CUPS server is sending two advertisements, one of which is for the mystery 0.0.0.0 server. But anyway we'll let that one go through to the keeper for now. [Please also ignore my dodgy host naming scheme]

When connected with the wireless network, the first advertisement is the same, but the second one is partially corrupted, with most of the IP header being zeroed out:

Invalid IP packet (140 bytes), claims 0 byte IP header length
Data:
«00»«00»«00»«00»«00»«00»«00»«00»«00»«11»«00»x«C0»«A8»«00»«05»«C0»«A8»«00»«FF»«02»w«02»w«00»x«00»«00»
1006 3 ipp://lola.geekflash.com:631/printers/Samsung
"" "ML-1710P" "Samsung ML-1710 Foomatic/gdi (recommended)"

So the mystery (partially) solved. Somewhere in the ethernet-to-wireless transition the second CUPS advertisement is corrupted. Yes that does seem like a pretty bizarre bug, but the packet sniffer doesn't lie.

A quick visit to the Netgear support site revealed that I was already running the latest firmware. I tried reverting to the previous version, but that didn't help. So it looks like I've now got an excuse to upgrade to a new wireless router. WRT54G, anyone?

3 Comments

Posted by
Chris
2005-02-27 09:45:28 -0600
#

I've got this problem with all broadcast packets. I noticed it first because I'm trying to use the router to bridge DHCP from a server. Can't find a solution though :(


Posted by
alastair
2005-02-27 09:45:28 -0600
#

This probably doesn't help you, but I ended up getting that WRT54G.


Posted by
Chris
2005-02-27 09:45:28 -0600
#

Oddly enough so did I (for home) but I'm stuck with these Netgear.... "things"... at work. BusyBox is the mutts nips!