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OSPF and MTU Mismatch

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  • 1.  OSPF and MTU Mismatch

    Posted 11-06-2019 01:23

    Hi All,

     

    I try to connect 1 ex3200-48t [11.4R5.5] with mx-10003 17.4R2-S4.1.

    Note: I can not modify any configuration on the ex3200-48t i can only play with the mx.

    Problem: I need to create an OSPF peering between them but i got this error on the mx

     

    Bla@bla.bla> show log ospf-debug | match mtu
    Nov 6 17:50:16.370895 options 0x50, i 1, m 1, ms 1, r 0, seq 0xd974d59a, mtu 8982
    Nov 6 17:50:16.370922 OSPF packet ignored: MTU mismatch from x.x.x.4 on intf xe-1/1/10:0.350 area 0.0.1.94
    Nov 6 17:50:18.021625 options 0x50, i 1, m 1, ms 1, r 0, seq 0x5ccedeb4, mtu 1500
    Nov 6 17:50:20.710752 options 0x50, i 1, m 1, ms 1, r 0, seq 0xd974d59a, mtu 8982

     

    On the ex3200-48t (IP x.x.x.4) I see

    set interfaces vlan mtu 9000
    set interfaces vlan unit 350 family inet mtu 8982

     

    On the mx I try to run the following

    bla@bla# show | compare
    [edit interfaces]
    +   xe-1/1/10 {
    +       mtu 9000;
    +   }
    
    [edit]
    bla@bla# commit
    and then

    bla@bla# commit check
    [edit interfaces xe-1/1/10:0 unit 350 family]
      'inet'
         Family MTU 8982 is too large relative to device MTU 1518; Protocol overhead should be 18
    error: configuration check-out failed
    
    [edit]
    bla@bla#
    

    Of course L3  interface xe-1/1/10:0 unit 350 on MX is connected to L3 interface vlan unit 350 on ex. Direct connection.

    Any idea how can i fix this?

     

    Thanks. 



  • 2.  RE: OSPF and MTU Mismatch

     
    Posted 11-06-2019 01:58

    Hi, 


    Can you check interface MTU of 9000 has been correctly applied:

    show interfaces xe-1/1/10 | match MTU

    Cheers, 
    Ashvin



  • 3.  RE: OSPF and MTU Mismatch

    Posted 11-06-2019 02:30

    Hello

     

    On both device you can run

    show ospf interface detail

    this will show you the associated MTU in use by OSPF

     

     



  • 4.  RE: OSPF and MTU Mismatch
    Best Answer

     
    Posted 11-12-2019 13:38

    You have a WRONG configuration

     

    Your physical interface is xe-1/1/10:0 NOT xe-1/1/10

     

    Try:

    delete interface xe-1/1/10

    set interface xe-1/1/10:0 mtu 9000