Rasterisk Freeze On 4G Link

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Hello,

I’m remotely managing an asterisk setup using an OpenVPN client on this Asterisk box, connecting to an OpenVPN server of mine).

This box is mainly connected to PSTN. It is also connected to the Internet, only for remote management.

The former ADSL link has recently been replaced by a new 4G link (UMTS).

I’m connecting to this box from a Debian Jessie/Gnome Terminal combo.

With this new link, whenever I launch a vim, a nano or a rasterisk session, my terminal freezes (rasterisk) or remains empty (nano, vim).

When a session is frozon, I can open a new one at the same so it excludes a basic connectivity loss.

What would you suggest ?

Best regards

PS: I was about to determine best MTU value but I always thought a punishment for a bad MTU value would be a lower throughput, not a screen freeze. Is it correct ?

7 thoughts on - Rasterisk Freeze On 4G Link

  • Please set correct MTU at server side, it is definitely an MTU issue.

    Sent from my iPhone

  • Usually incorrect MTU gives you this effect. Use ping with MTU size set to test and find what works.

    You will probably also break it with any large text dump eg cat /var/log/syslog will also do it

  • 2016-03-03 18:08 GMT+01:00 Duncan Turnbull :

    I think its value: it’s 1272, which amazes me.

    Yes “cat /var/log/syslog” also broke my console.

    Why would my console break because of inadequate MTU and other PC on the same location, seem unaffected ?
    Because, they most probably mostly use SMTP and HTTP ?

    Is possible to simulate a given MTU on a LAN to reproduce such freezes ?
    (the remote location is at the other side of the country and I would like to prepare things as much as possible).

  • These are not Asterisk related questions. It is a common problem. Google is your friend. Try something like ‘console stalls with big packets’.

    To answer your question “why”, it’s simple. “Because the big packets are being dropped”.

    Pete

  • > With this new link, whenever I launch a vim, a nano or a rasterisk session, my terminal freezes (rasterisk) or remains empty (nano, vim). I think you need to go through a router or some device that can constrain the MTU. But live changing your server MTU should be straight forward as openvpn should try and reconnect, and you can change the server back. I haven’t lost connectivity before with this

    Also the session is probably timed out rather than gone, in 10-15 mins maybe less it will come back (or does for me)

    Cheers Duncan

  • Hello,

    You need to determine the correct MTU value by doing the following:

    ping http://www.google.com -f -l 1400 and you go up or down

    An example:
    1440 Max packet size from Ping Test
    + 28 IP and ICMP headers
    1468 is your optimum MTU Setting

    Reference : http://www.tp-link.fr/FAQ-190.html

    Once you determine the correct MTU you just set it on the VPN server, it will not break any connection the worst will be slow connection that is all.

    From my experience the MTU value for 3G was 1400.

    Best regards

    Toufic

    From: asterisk-users-bounces@lists.digium.com
    [mailto:asterisk-users-bounces@lists.digium.com] On Behalf Of Duncan Sent: Thursday, March 03, 2016 9:02 PM
    To: Asterisk Users Mailing List – Non-Commercial Discussion

    Subject: Re: [asterisk-users] Rasterisk freeze on 4G link

    session, my terminal freezes (rasterisk) or remains empty (nano, vim).

    a basic connectivity loss. Usually incorrect MTU gives you this effect. Use ping with MTU size set to test and find what works.

    I think its value: it’s 1272, which amazes me.

    You will probably also break it with any large text dump eg cat
    /var/log/syslog will also do it

    Yes “cat /var/log/syslog” also broke my console.

    Why would my console break because of inadequate MTU and other PC on the same location, seem unaffected ?

    Because, they most probably mostly use SMTP and HTTP ?

    Is possible to simulate a given MTU on a LAN to reproduce such freezes ?

    (the remote location is at the other side of the country and I would like to prepare things as much as possible).

    I think you need to go through a router or some device that can constrain the MTU. But live changing your server MTU should be straight forward as openvpn should try and reconnect, and you can change the server back. I
    haven’t lost connectivity before with this

    Also the session is probably timed out rather than gone, in 10-15 mins maybe less it will come back (or does for me)

    Cheers Duncan