Currently the icmpping* simple checks have size field that could be used for monitoring large packet support in the network.

However, sending larger packets than link MTU causes packets to be fragmented (in IPv4), which makes it impossible to monitor network availability for 1500-standard packets with the simple checks.

I'm proposing adding support for DF-bit (Don't Fragment) that would make it possible to use icmpping items for monitoring out-of-normal MTU situations in provider networks.

In practice, for example, an ICMP payload size of 1472 (= 1500 minus IPv4 and ICMP headers) could be specified along with the proposed DF-bit option, and the item would fail if the end-to-end MTU is below the expected 1500 bytes. (This is the normal way of verifying the link MTU.)

https://fping.org/fping.8.html says there is an option for it in Fping:

M, -dontfrag

Set the "Don’t Fragment" bit in the IP header (used to determine/test the MTU ).

The use of DF-bit would be configured in the options field in the items ("dont_fragment", for example).