3/03/2020

Arista EOS MTU Behavior (1)

Summary:
In this series of blogs, I will cover the MTU (Maximum Transmission Unit) behavior on Arista Jericho-based routers. Here is the summary:
  • 1. MTU enforcement happens on the egress interfaces. 
    • So MTU is not MRU (maximum receive unit), large size packets are NOT dropped at ingress interfaces
  • 2. Arista MTU is layer-3 MTU on Jericho chipset:
    • 2.1 The MTU enforcement is only for routed packets, no action on switched traffic
    • 2.2 The actual packet size is MTU size plus L2 header size, which is 14-byte for L3 routed interface or 18-byte for the trunk interface
  • 3. IPv4 packets are fragmented by router CPU and capped by CoPP

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