Mitel 5320 over VPN - Strange Behaviour

[pokeyhat]

Hello - first post here, please be gentle!
I'll start by letting you know i'm not a voice guy by any means - but have been landed with a strange voice type problem so am reaching out to this fine community! 

So - Mitel 5320 IP phone, site to site VPN back to the controller - the phone registers, and it is possible to log in and make calls. All good right?
Almost - any kind of communication between controller and phone is woefully slow - TFTP Main hangs for approximately 9 mins, Contacting Server the same - as well as the check to Upgrade HTML Apps and logging into the phone - all take around 9 mins to complete - once this very long protracted dance is complete - the phone works fine, but it's obviously not a workable solution when everything takes so long!

Has anyone out there ever seen this before and more importantly been able to solve the issue? Tearing out what little hair i have left! Appreciate any help you can offer - thanks in advance!

Holding out for a hero........

[ZuluAlpha]

First things first - is the actual bandwidth available? Voice traffic isn't very high bandwidth so a frayed cat 5 cable on the remote end might be handling the voice traffic but when it comes to anything else good luck.

[dilkie]

sounds like an MTU issue.

[pokeyhat]

First things first - is the actual bandwidth available? Voice traffic isn't very high bandwidth so a frayed cat 5 cable on the remote end might be handling the voice traffic but when it comes to anything else good luck.

Loads of bandwidth available - sorry, should have said that!

[pokeyhat]

sounds like an MTU issue.

Care to expand? MTU is the same at both sides of the VPN link as far as i can tell...

[dilkie]

usually the MTU of a vpn link is smaller than the MTU of ethernet, which gets discovered dynamically (MTY discovery)... you don't have any icmp (or firewall) restrictions on link traffic, do you?

[dilkie]

otherwise, getting a pcap of the set's traffic might be your best next step.

[Dogbreath]

sounds like an MTU issue.

Plus one.

How about Teleworker Network Analyzer "Connect Test"? Would give more useful diagnostics than a handset, but not sure if it's valid against MiVB rather than MBG.

[pokeyhat]

Guys - thanks for the input - further testing being done over the weekend - i'll be sure and report back

[pokeyhat]

So - here's the story. MTU was not the issue - i was able to verify that remote sites using various methods to connect had the same MTU as the site i was using, but these other sites were working.

Long story short - the problem was sorted by using firewalls from the same vendor at both sides to terminate the VPNs - i had been using different vendors at either side. In my mind - this shouldn't matter - tunnel came up, everything worked as it should except the long delay in the phones talking to the controller. Swap out the phone side firewall with one the same make as central site - problem goes away. Can't really explain it - but at least can move on with my life. 

Thanks again for your input guys - appreciated!