Mac – Setting MTU Per Destination Host

The short answer: "It depends".

The longer answer:

normally the TCP implements path MTU discovery algorithm (RFC1191).

However, the problem is that the middleboxes sometimes drop the ICMP messages "Fragmentation Needed, DF bit set" that are used for this. That said, it is usually infrequent - so you should be ok with the default MTU of 1500 - assuming your side does not filter ICMP unnecessarily, the failures to connect will be caused by the misconfigurations on the client side.

the MTU of 576 is assumed if the host does not implement the Path MTU discovery (if you explicitly disable it). This will cause lower performance for the connections, so better do not touch it.

So, normally 1500 should be a reasonable MTU to run in the vast majority of the cases - unless a very specific case where the firewall administrator on your side is overzealously blocking ICMP and the remote client is connecting via a path with a link inbetween that has a smaller MTU. But still, this case is best fixed by reconfiguring the firewall, so again 1500 should be fine.

Welcome to the strange and mysterious world of jumbo frames! It's normal that jumbo frame ethernet gear has MTU > 1518 and < 65K byte and you have to find a setting that is the lowest common denominator across your L2 domain to enable proper jumbo traffic.

My guess is that your ping/ICMP implementation only works for 8192 bytes payload, so 8164 + 28 (20 for the IP header and 8 for the ICMP header) gives you 8192 bytes.

MTU 9216 is also a standard 9K MTU on a lot of Cisco's gear, so my assumption is that Netgear wanted to be ''compatible'' to that.

Also note that MTU size specification should be taken seriously, a lot of vendors don't include 802.1Q (vLANs) or even L2 frame headers. Check with your switch vendor's documentation what they really specify when they're talking about MTU size.