Rv082, Ipsec Mtu Setting

Discussion in 'Cisco Small Business Routers and VPN Solutions' started by moored99, Jul 4, 2007.

  1. moored99

    moored99 LI Guru Member

    I have just installed 2 x RV082 in different locations, both using 2 x ADSL links to different ISP's (ADSL modems in bridged mode, PPPoE is controlled from the RV082) when I looked at the FIRWALL section I noticed the MTU was set to Auto = 1500 (GRAYED OUT) while my customers could ping each way terminal services across this IPSEC VPN were extremely slow and dropped out all the time. I changed the MTU setting in the firewall settings tab to = 1454. From that point forward everything seemed to start working.

    Question: MTU=1454 is this the best value to use?
  2. erniemunozb

    erniemunozb LI Guru Member

    Hi Moore,

    Try to ping between both sites with the tunnel up and running using the following command on a Windows DOS prompt

    ping anyipontheothersite -f -l 1454

    If the response to the ping is something like "Packet needs to be fragmented but DF set", try reducing in 8 the number after the -l until you get the response in milisecs (meaning the standard ping response") and assign this value to the MTU setting on both sites.

    If you don't get a significant improvement, a DNS check up would help.

    Hope this help to you.
  3. moored99

    moored99 LI Guru Member

    thank you for your advise.

    I started pinging from 1500 - 1468 and got "Packet needs to be fragmented but DF set"
    At 1460 i received no fragmented message so I will choose 1454 as my MTU value unless others advise against.
  4. binderz77

    binderz77 Network Guru Member

    1454 should work. When the RV082 has the MTU setting to Auto : it sets its MTU to 576, so you should always set it to Manual and a value which works for you.
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