Draytek suddenly stops calls on VoIP Unlimited trunk

Discussion in '3CX Phone System - General' started by viper, Jun 22, 2011.

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  1. viper

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    Hi,

    We've been using a 3CX setup for a while now, suddenly this morning calls stopped working. On investigation it appears the Draytek Vigor 2820 (fw 3.3.5_232201) is to blame. Looks like a UDP packet size issue but it has never been a problem before and no changes were made overnight. Everything has been rebooted and the only thing I can find is a suggestion to UNTICK the "Accept large incoming fragmented UDP or ICMP packets" option - done, rebooted and no change.

    As soon as I route the SIP traffic out of the data network (using ZyXEL USG) everything is fine.

    Anyone got a suggestion on how to fix this?

    Thanks,

    Tom
     
  2. harv

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    Hi Tom,

    Did you get anywhere with this - I'm seeing a very similar thing.

    We're using dual ADSL with pfsense and VOIP-Unlimited as our provider.

    The ADSL which the SIP should be routed over is running in PPOE mode, so I guess in theory the fragmented packets setting in the router should have no effect. However, the VOIP-UL traces still show fragmented packets as the reason we aren't getting inbound calls! Very frustrating. The previous configuration using Smoothwall and PPOE pass through worked much better!

    I've just tried turning STUN off.

    I've tried messing with the MTU settings, but no joy at all.

    Anyone got any ideas?

    Harv
     
  3. viper

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    Hi,

    We are still working through the issue with Draytek and VoIP Unlimited - it looks likely to be an issue with how the T38 (Fax over IP) is implemented. Once we have made some more headway will let you know.

    In the meantime if you find any solution please let me know.

    Thanks,

    Tom
     
  4. davidbenwell

    davidbenwell Active Member

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    We come across this alot with VoIP Unlimited and we manage to get this working with the Draytek router by setting the MTU to the max size of 1428 and it works, We are resellers for VoIP Unlimited so if you need any help getting this working, give me a call 01702 66 88 36
     
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  5. viper

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    Hi,

    We are also VoIP Unlimited resellers and this has now happened on a few accounts, suddently overnight something happens and then the calls no longer connect - all have different hardware. I've changed hardware, firmware, MTU, disabling firewalls and nothing seems to help the call complete. As soon as we take if via a different route (in this case) the calls work without an issue. Val at VoIP U has said it is due to the T38 having large packet support but seems not to like any hardware we throw at it.

    Any other ideas?

    Thanks, Tom
     
  6. davidbenwell

    davidbenwell Active Member

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    We are in talks with Richard and Rob at VoIP Unlimited to see if they can adjust their network as its only VoIP Unlimited that this happens too. all other VoIP Providers have no issues.

    They claim its to do with the T.38 like you say. Richard is going to be giving me a call back tomorrow.
     
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  7. harv

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    Hi David,

    Sorry for the slow reply, I've been having another fiddle with this.

    I tried setting the MTU to 1428, both in the pfsense firewall (the router is running in PPOE pass-through) and on the router. This had no effect at all :(

    This morning, I've just replaced the Draytek 2820 with a Netgear DG834v2, set up in PPoE modem mode. The problem remains, so it looks like PFSense and VOIP-Unlimited aren't friends.

    In terms of the firewall configuration, the 3CX ports are all non-natted, all email etc works perfectly. I've tried the Clear invalid DF bits instead of dropping the packets setting and also disabling the firewall scrub setting.

    I'd be willing to sacrifice fax over IP just to get this working again.

    Hopefully Richard will have a positive answer for you today.

    If you can think of anything else which I should be checking or trying then I'd be really keen to hear/try.

    Regards,

    Harv
     
  8. davidbenwell

    davidbenwell Active Member

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    I have spoken to Richard just now on this.

    Would you be able to put back your Draytek 2820 router and give us remote access.

    We have managed to get theses working with VoIP Unlimited and have a few customers on them.

    if so, please email support@it-communicationsltd.co.uk and i will send over the details to get remote access.
     
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  9. harv

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    Dave,

    Just thought I'd update you on the status of the problem.. It appears something has changed at VOIP-Unlimited.. looking at the call traces this morning,

    It appears they have dropped their invite packet size from about 1514 to approx 1346 bytes, this means it's below the MTU, so all works once more.

    Have you seen this replicated in your traces?

    Harv
     
  10. viper

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    Hi,

    I've been talking to Steve at VoIP U about this along with our distributor - the distributor kindly sent VoIP U some equipment they could try my configs on and following that VoIP U have changed the header packet to enable the calls to be "slimmed" down and hopefully in 99.9% of cases the calls will complete with no problem - they did say that the odd call may still drop due to fragmented packets.

    Thanks,

    Tom
     
  11. harv

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    That's fantastic news.. thanks for the update!

    It's nice to see the reason for why everything has suddenly started working. I thought I was going to go mad.

    I also thought I was going to have to ditch pfsense, which it a shame, as it's an amazingly flexible open source firewall. All the 3cx ports pass straight through without any kind of NAT messing about.

    Harv
     
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