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Eircom VPN - MTU Settings

  • 12-12-2007 10:25pm
    #1
    jamesd
    Registered Users, Registered Users 2 Posts: 3,464 ✭✭✭


    Hi,

    I have setup a site to site vpn with 2 sonicwall routers (TZ150 and a TZ170 with PPPOE ) with 2 netopia boxes in bridged mode - the vpn is working but slow even though its a 3mb line - Speaking to sonicwall today and they told me to update my firmware on both boxes and also to get the correct MTU set on both my sonicwalls. By default its set to 1500 - Is 1492 the correct MTU?


Comments

  • #2
    Rattlehead_ie
    Registered Users, Registered Users 2 Posts: 1,884 ✭✭✭Rattlehead_ie


    There is no correct or incorrect MTU size, it depends on what type of security encryption you and then your ISP are using.

    Best advise is set it down to about 1450 and work up in increments of 8. i.e. 1458, 1466, 1474, 1482 and see which one is the highest you can go.


  • #3
    lynchie
    Registered Users, Registered Users 2 Posts: 2,013 ✭✭✭lynchie


    jamesd wrote: »
    Hi,

    I have setup a site to site vpn with 2 sonicwall routers (TZ150 and a TZ170 with PPPOE ) with 2 netopia boxes in bridged mode - the vpn is working but slow even though its a 3mb line - Speaking to sonicwall today and they told me to update my firmware on both boxes and also to get the correct MTU set on both my sonicwalls. By default its set to 1500 - Is 1492 the correct MTU?

    Is it a leased line you have, i.e. 3Mb Synchronous? Or is it standard 3Mb Eircom DSL line? If so, the max speed you are going to get between them is the upload speed of the line probably 384Kb and not the full 3Mb


  • #4
    jamesd
    Registered Users, Registered Users 2 Posts: 3,464 ✭✭✭jamesd


    Its a 3Mb Eircom DSL line between them - they have 2 pcs in the 2nd site and they both want to use the file and print server in the 2nd site.I set the mtu on both sonicwalls to 1492 and updated the firmware on both to the latest versions today but still slow.


  • #5
    jamesd
    Registered Users, Registered Users 2 Posts: 3,464 ✭✭✭jamesd


    Rattlehead_ie wrote: »
    There is no correct or incorrect MTU size, it depends on what type of security encryption you and then your ISP are using.

    Best advise is set it down to about 1450 and work up in increments of 8. i.e. 1458, 1466, 1474, 1482 and see which one is the highest you can go.


    How do I test which mtu works?


  • #6
    ob
    Closed Accounts Posts: 164 ✭✭ob


    TCP Optimizer is great for finding the MTU. Temporarily replace the sonicwall with a PC/laptop and run it to find the MTU. That said, I think it's usually 1492 for Eircom.

    http://www.speedguide.net/downloads.php
    Its a 3Mb Eircom DSL line between them - they have 2 pcs in the 2nd site and they both want to use the file and print server in the 2nd site.I set the mtu on both sonicwalls to 1492 and updated the firmware on both to the latest versions today but still slow.

    It's only 3Mb download though, 384k upload is probably where the problem is for file transfers.


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  • #7
    lynchie
    Registered Users, Registered Users 2 Posts: 2,013 ✭✭✭lynchie


    jamesd wrote: »
    Its a 3Mb Eircom DSL line between them - they have 2 pcs in the 2nd site and they both want to use the file and print server in the 2nd site.I set the mtu on both sonicwalls to 1492 and updated the firmware on both to the latest versions today but still slow.

    Then the max speed you are going to get between both sites is 384Kb. What speeds are you seeing now?


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