Limit the maximum MTU to 9216 bytes?

[ipspace]

It looks like none of the devices netlab supports uses anything but Ethernet for the "physical" interfaces, and the maximum jumbo frame size on Ethernet seems to be 9216, so it might make sense to set the upper bound of the mtu attribute to 9216 (with a footnote in the documentation explaining how to raise it)

Any objections? /cc @jbemmel @ssasso @steffann @sdargoeuves @ddutt

[sdargoeuves]

Just looking at a cisco iosv, from a configuration perspective they allow up to 9600 🤷

d5xr01(config-if)#mtu ?
  <64-9600>  MTU size in bytes

A Juniper seems to go to 9192:

vagrant@c0xr03# set interfaces ge-0/0/2 mtu ?
Possible completions:
  <mtu>                Maximum transmit packet size (256..9192)
[edit]

Regarding my usage, I have only one interface where I have set the mtu to 1500 to create a mismatch, for all the other use cases around MTU, I have some playbooks creating different scenarios.

Long story short, 9216 sounds good to me!

[ddutt]

9216 sounds fine to me as well.

[ipspace]

Thank you, implemented ;)

[jbemmel]

On Dell OS10 9216 is the maximum Ethernet MTU, for IP level MTU (as used by Netlab) the maximum would be 9184:

Mode of IPv4 Address Assignment: not set
    Interface IPv6 oper status: Disabled
MTU 9216 bytes, IP MTU 9184 bytes
LineSpeed 25G, Auto-Negotiation off

At the same time, Cumulus does (claim to) support a 9216 IP level MTU size