MTU/L2 MTU configuration help for bridge/VLANs

RouterOS General
1

I’m having an issue getting end to end MTU of 9000 set within my CRS317 switch, running RouterOS v6.48.1. I used the command below to successfully set the mtu and l2mtu on the physical ports. This is reflected in WInBox for each port. The bridge now also has a L2 MTU of 65535 but an Actual MTU of 1500. I can’t find the proper CLI command to set the bridge actual MTU to 9000. I can do it through Winbox, but I need the CLI command.

Any help would be appreciated to get the bridge set to MTU of 9000. MTU related commands that I’ve run:

/interface ethernet
set sfp-sfpplus1,sfp-sfpplus2,sfp-sfpplus3,sfp-sfpplus4,sfp-sfpplus16 l2mtu=10218
set sfp-sfpplus1,sfp-sfpplus2,sfp-sfpplus3,sfp-sfpplus4,sfp-sfpplus16 mtu=9000

/interface vlan
set “2611-MGT” mtu=9000
set “2612-vMotion” mtu=9000
set “2613-VM” mtu=9000

2

MTU (without any prefix) is a parameter of an L3 interface, hence the right command is /interface bridge set name-of-the-bridge mtu=9000. Setting it at the other ports of the bridge, i.e. the ethernet/sfp ones, makes no difference as this parameter is ignored while the ethernet/sfp interface is a member port of a bridge.

The row of /interface bridge aggregates configuration parameters of

  • the bridge itself (as in “virtual switch”),
    a virtual port of that virtual switch,
    a virtual port of a router connected to that virtual port of that virtual switch.

So the MTU is a parameter of the 3rd one (virtual port of a router).