Custom MTU for bridge network

We run Nomad on OpenStack instances which have a default MTU of 1450 for VXLAN networks. We are trying to figure out if it’s possible to set the MTU of the bridge network Nomad uses for Consul Connect services. We tried making a custom bridge network with a specified MTU, but it looks like Consul Connect only works with the built-in default bridge network which doesn’t currently have a way to specify it.

According to the bridge CNI documentation, the MTU “Defaults to the value chosen by the kernel.” Is there some way to use some OS level network setting to get the default MTU to match our interface properly? Or is the only option to try to update Nomad to allow specifying a custom MTU value for the built-in bridge?

Hi @Kimahriman; unfortunately there is no way currently to inform Nomad of which MTU to use for the bridge network. I am also not aware of any way to change the kernel level value which is used by default, although I might be missing knowledge here.

I have raised this issue which would allow operators to supply their own CNI configuration for use with the bridge network. If you could give this a thumbs up, that would be useful for internal roadmapping.

jrasell and the Nomad team