Switching

last person joined: yesterday 

Ask questions and share experiences about EX and QFX portfolios and all switching solutions across your data center, campus, and branch locations.

  • 1.  ospf and big frames

    Posted 02-07-2012 08:22

    Hi,

     

    I have a EX3200 running 10.3R1.9, ospf is enabled on one of the interfaces, but when I set the mtu size to 9216 then the ospf routes disappear.

    The ospf database stays the same also the neighbors are listed, but the routes are gone.

    When deleting the mtu setting, then the routes come back again.

     

    Is this normal behavior?



  • 2.  RE: ospf and big frames

    Posted 02-07-2012 08:57

    It's normal, and a requirement of RFC 2328 section 10.6...

     

    If the Interface MTU field in the Database Description packet
        indicates an IP datagram size that is larger than the router can
        accept on the receiving interface without fragmentation, the
        Database Description packet is rejected.


  • 3.  RE: ospf and big frames
    Best Answer

    Posted 02-08-2012 06:24

    Yes - you'll need to make sure all neighbouring routers that are adjacent on this interface have their MTU sizes set the same, otherwise OSPF will not establish.

     

    Cisco have a configuration knob ignore-mtu-mismatch which gets around this, but Junos enforces it.

     

    Hope this helps