[asterisk-dev] IAX hardphone

Kevin P. Fleming kpfleming at digium.com
Tue Feb 15 11:11:13 CST 2011

On 02/15/2011 10:58 AM, Mihai Balea wrote:
> On Feb 15, 2011, at 11:21 AM, Bill Shaw wrote:
>> Just thought I'd confirm that the UDP checksum being incorrect was my problem (thank you Mihai),  and also that Wireshark incorrectly handles the UDP checksum.  I've corrected my checksum routine and deleted Wireshark - fallen back to Ethereal.
> Glad I could help.
> Weird that your copy of Wireshark did not flag this - I'm using Wireshark on Mac OSX (v 1.4.3) and it pointed me to it. And, after all, Wireshark is the new Ethereal, they renamed the project a while back.
> Maybe it was just a buggy version or maybe just some settings...

In addition, there's really no such thing as a 'disabled' UDP checksum; 
UDP checksums are not optional in the protocol, although some endpoints 
can be configured to not compute/check them. Even in that case, the 
checksum field will still be present in the UDP header, and will usually 
have a constant value.

It is possible that Wireshark senses a particularly common constant 
value (like all zero) and reports that the endpoint must be configured 
with UDP checksum generation/checking 'disabled'... which I suppose 
would be better than it reporting every single packet with a UDP 
checksum error for such an endpoint.

Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kfleming at digium.com
Check us out at www.digium.com & www.asterisk.org

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