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Campus Core CX uplink mtu setting, L2 and L3 or just L3?

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  • 1.  Campus Core CX uplink mtu setting, L2 and L3 or just L3?

    Posted Jan 22, 2024 05:09 PM

    I'm working through a new design and have come across the L2/L3 mtu configurations on CX switches...  https://www.arubanetworks.com/techdocs/VSG/docs/020-campus-deploy/esp-campus-deploy-050-wired-core/

    I've noticed that the ESP wired core design only has ip mtu 9198 set on the p2p interface to the aggregation.

    interface 1/1/1 
      description CORE_TO_AGG1
      no shutdown
      ip mtu 9198
      ip address 172.18.103.2/30
      no ip ospf passive
      ip ospf network point-to-point
      ip ospf 1 area 0
      ip pim-sparse enable

    But further down in the design, the Internet Connectivity Aggregation has both L2 and L3 mtu's set.

    interface 1/3/11
        description RSVCP-INET
        no shutdown
        mtu 9198
        routing
        ip mtu 9000
        ip address 192.168.8.9/31
        ip ospf 1 area 0.0.0.0
        no ip ospf passive
        ip ospf network point-to-point

    Why does the Core to Agg connection not have the L3 and L2 MTUs set?  If I only set the ip mtu how is it not fragmented with a L2 mtu of a default 1500?

    Thanks



  • 2.  RE: Campus Core CX uplink mtu setting, L2 and L3 or just L3?

    Posted 30 days ago

    For the Campus Core CX uplink MTU setting, is it necessary to configure it for both Layer 2 (L2) and Layer 3 (L3), or is it sufficient to configure it only for Layer 3? Share your insights on whether both layers need MTU settings or if L3 alone is appropriate.




  • 3.  RE: Campus Core CX uplink mtu setting, L2 and L3 or just L3?

    Posted 29 days ago

    That's my question as well... 




  • 4.  RE: Campus Core CX uplink mtu setting, L2 and L3 or just L3?

    EMPLOYEE
    Posted 28 days ago

    IP MTU controls the size of IP packet for routing. you can set it on SVI or routed only port (ROP) 

    The MTU at layer 2 is about the size of Ethernet frame.

    generally for a CX switch ROP, I would set both ip mtu and mtu to be the same 9198.



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