RV0xx default MTU values behind cable/dsl modems

Discussion in 'Cisco Small Business Routers and VPN Solutions' started by binderz77, Sep 22, 2006.

  1. binderz77

    binderz77 Network Guru Member

    This questions is regarding the default MTU value when the RV0xx (016, 042, 082) is used behind a cable/dsl modem.

    I am very interested in knowing the default MTU value for Rv016 and RV042. For RV082 firmware 1.3.2 I was able to see that when this router is used behind a cable modem (Motorola's SBG900 or SB5120), the router sets the MTU value automatically on the WAN side to 576. Earlier I had the same problem with WRV54G F/W 2.37 and 2.39.2.

    As I cannot buy RV041 or RV016 ( for I already have RV082 and WRV54G ) I would appreciate if somebody provide me with this information.
  2. pablito

    pablito Network Guru Member

    You should typically see an MTU of 1500 when behind an ethernet device like a cable modem or any other router that is between you and the net (including a DSL router if you are on the LAN side). PPPoE DSL MTU will vary but common MTU is 1492, mine goes to 1452. I've heard of some RVs auto setting to 576 which is not good. You would want to manually set your MTU in that case. The latest beta firmware seems to do a much better job and in fact solved an MTU related problem I was having with 1.3.2
  3. binderz77

    binderz77 Network Guru Member

    "The latest beta firmware seems to do a much better job and in fact solved an MTU related problem I was having with 1.3.2

    I am going to try with 1.3.2.

    Can anyone tell about default MTU value on the WAN port for RV042 behind a cable modem?
  4. Toxic

    Toxic Administrator Staff Member

    you should set the MTU to manual and use 1500 for cable
  5. YeOldeStonecat

    YeOldeStonecat Network Guru Member

    I've always manually set the MTU on every single brand/make/model router that I've installed. The "auto" function is not something I trust, too many variables in the way that can throw it off.

    1500 for cable/T and bridged DSL
    1492 for PPPoE DSL (I've read some people in Europe go even lower for this..I've just worked with various ISPs across several states in my area of the US)
  6. quattrohead

    quattrohead Guest

    Just discovered that setting the MTU manually has fixed my Sunrocket VOIP using an AC211.
    Could not for the life of me work out why the ATA would work plugged into the RV042/082 only if the RV was plugged into a Netgear router !!!!!!
  7. binderz77

    binderz77 Network Guru Member

    I am glad for you Quattro....
    I had the same problem...
    My SIP based videophone won't work behind RVxxx and WRV54G ( F/W ver. 2.37 onwards ) until I set the MTU to manual.
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