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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 Jan 23, 2024 10:56 AM

    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.


    Original Message


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

    Posted Jan 24, 2024 09:08 AM

    That's my question as well... 


    Original Message


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

    EMPLOYEE
    Posted Jan 26, 2024 03:52 AM

    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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    Original Message