Mitel phones not liking the SYN/ACK

[parvikram]

I have two captures. In one, I see a handshake from the phone to the Voice Server (working capture). In the non-working one, I do not see an ACK from the client after the SYN/ACK from the Voice Server.

Initially I thought it might be a routing issue since maybe the SYN/ACK from the server is not reaching the client or the ACK from the client is not reaching the server. But traffic other than Voice is going fine back and forth between the client (Mitel Phone) and the server. There is no FW between them.

Any idea why we do not see any ACK from the Mitel phone back only for the Voice traffic. I thought maybe something in the SYN/ACK which the phone is not liking perhaps. I saw the TCP options , in the failing case the order of appearance of the TCP options is different. The fingerprint of the failing scenario shows the windowscale option first, followed by MSS and NOP. The successful scenario shows MSS,NOP,Windowscale .
WOULD THIS CAUSE THE MITEL PHONE TO NOT SEND BACK AN ACK SINCE THE PHONES ARE NOT REGISTERING.

[ralph]

What system are you trying to connect to?

Ralph

[parvikram]

Hello Ralph,

  Thanks for the response. It's a Mitel phone connecting to a Mitel Voice Server.  Not sure about the version and exact make. Do you need me to find that out ? I can if it helps.

[ralph]

I wanted to be sure your post was in the correct forum section.
I'll assume it is a Mitel 3300 and move the post there.

Ralph

[parvikram]

Thanks Ralph. But I'm not getting any answer. I really suspect some bug in the TCP Stack of the Mitel phone. I wanted to confirm the same.

[johnp]

I don't think anyone knows the exact nature of your problem. Maybe you could tells us what your issue is in simpler terms, i.e. one phone boots up properly while another constantly reboots or something similar.

[sarond]

So the phone and the server are on different subnets, VLANs..., I know you said you checked routing but is it possible to get a laptop on the voice network to see if you can reach the server, this will at least eliminate the phone being a problem.

[acejavelin]

There is no issue with the Mitel IP stack, it is either misconfigured or you have malfunctioning/non-standard equipment. Mitel has been doing IP phones and services for a very long time... They have it down.

If you could give us more information on the scenario this is and what is not working, we could probably help more.

[parvikram]

I'm attaching the working and non-working captures. You can see that in the non-working one, the phone receives the SYN/ACK but does not respond with an ACK. I do not suspect routing since, the same phone is communicating with a different TCP port 20001 on the same server. But this time, the traffic is UDP. I seriously still think , its something to do with the TCP stack of Mitel . I know it's been working for ages, but we do see it pretty obvious here, that with a few TCP options realigned and a different MSS value than the working capture, the phone does not respond with an ACK.

[ralph]

What exactly isn't working?   What was the issue that caused you to do a packet sniff in the first place?

Ralph

[parvikram]

The issue is that the Mitel phones are not reigistering with the Voice server. The Voice Server IP is 172.16.8.2.

[ralph]

I couldn't open the ZIP file.

Ralph

[parvikram]

Hi Ralph,

  Let me upload it again. If you still can't open, then let me know your email address. I will send it across.

[ralph]

Got the file.

I admit I'm over my head on this one.
But I didn't see the DHCP request from the phone in either trace.  (I could have easily missed it)
The first question that comes to mind though is does the non-working phone work if it's plugged into the same port as the working phone?

Ralph

[parvikram]

They are connected to the same switch. It's just that the captures were taken on different phones . If you want we can try to take a working/non-working for the same phone but they the difference is still the same.

parvikram
CCIE (R&S)