[VoiceOps] Odd network problem with SIP

[Frank Bulk]

+1

-----Original Message-----
From: VoiceOps [mailto:voiceops-bounces at voiceops.org] On Behalf Of Ujjval
Karihaloo
Sent: Saturday, June 21, 2014 10:58 AM
To: Jay Ashworth
Cc: voiceops at voiceops.org
Subject: Re: [VoiceOps] Odd network problem with SIP

 wireshark can show chksum incorrectly at times. 

Ujjval K

> On Jun 21, 2014, at 9:37 AM, Jay Ashworth <jra at baylink.com> wrote:
> 
> I have a client using the Spitfire dialler on Win7 to dial via SIP to a
> carrier called VoxTelecom; I infer they're a virtual carrier because the
> SIP goes to their Sonus SBC at a single IP, but the media sessions go all
> over creation.
> 
> The client has been having completion trouble, and the dialler folks said
> "crappy circuit; too much jitter and packet loss", tested from the dialler
> using PingPlotter.  I don't think it was jitter, I think it was ping
response
> deviation; PingPlotter doesn't appear to actually test jitter.
> 
> But to tick the boxes, I had road runner out; they replaced a ubee D2
modem
> with their New Hawtness Arris D3 modem; no change.  All his analog
measurements
> were pristine, he told me.
> 
> So next step, check the router.  Log in to the Fortigate 40D; control
panel
> won't paint properly.  This *may* have been an IE10 compatibility mode
> red-herring, but I temporarily swapped it for a 20C, which I could talk
to.
> 
> Set up the inbound DNATs for udp/5060 SIP and upd/49152-49252 RTP.  
> 
> Ran some calls.
> 
> They're not seeing my ACK after they send me an SDP.  They get the invite,
but
> not the ACK.  I send RTP, but they don't bother cause they think the
call's
> not set up yet.
> 
> Wireshark on the dialler... that ACK packet *has a bad IP header
checksum*.
> 
> Not the earlier packets; just the ACK.  Huh?
> 
> So, assume it's the OS, somehow; reboot.  65 Windows updates and an hour
later...
> 
> Set everything back up, and run more test calls.  This time, the Invite
has a bad
> IP header checksum.  Look at clock, 6pm EDT.  Give up, go home.
> 
> I'm going to go back to the original router Monday morning, and check the 
> compatibility mode theory, but has anyone ever seen "just certain sent
packets
> show up with a bad IP header checksum, as monitored on-machine"?
> 
> (I know that the original 40D router might well *have* a problem, and that
the 
> checksum thing is orthogonal to the original problem -- since older pcaps
show
> clean setups -- but at least I can confirm I have the NATs configured
right.)
> 
> Cheers,
> -- jra
> 
> -- 
> Jay R. Ashworth                  Baylink
jra at baylink.com
> Designer                     The Things I Think                       RFC
2100
> Ashworth & Associates       http://www.bcp38.info          2000 Land Rover
DII
> St Petersburg FL USA      BCP38: Ask For It By Name!           +1 727 647
1274
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