For a given link type, how would a router calculate it's MTU?

I initially thought of it taking a brute force approach, using a binary search to figure out the point at which the link fails to support a packet.

But, wouldn't this require a protocol to get a response (ACK) (so the router knows the packet was actually successfully sent)

Does it use a timeout system?


1 Answer 1


Routers do not calculate the MTU. The MTU is a function of the layer-1/2 interface. For example, the MTU of ethernet is 1500 bytes. Other protocols will have other MTU sizes. That is something inherent in the interface and protocol, so a router or other device knows what the MTU of the link is.

  • There are 2 Ron's. It's confusing
    – Tobiq
    May 28, 2019 at 23:27
  • There used to be more. :)
    – Ron Maupin
    May 28, 2019 at 23:28
  • I’m the good looking one :)
    – Ron Trunk
    May 29, 2019 at 1:35

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