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EoIP: guarantee MTU of 1500

Posted: Fri Dec 08, 2023 5:03 am
by Kentzo
I'm planning a workaround to bridge interfaces of a legacy wireless station with interfaces of wifiwave2 AP. Since station-bridge is out, the plan is to use an EoIP tunnel as a VLAN trunk.
The wireless station has L2 MTU of 2290 and the wifiwave2 AP has L2 MTU of 1560 (see the 7.12 changelog).

What is the best approach to guarantee MTU of 1500 without fragmentation? Am I out of luck until Mikrotik fixes the wifiwave2 bug that limited L2 MTU of the wireless interfaces to 1560?

Re: EoIP: guarantee MTU of 1500  [SOLVED]

Posted: Fri Dec 08, 2023 6:01 am
by rplant
Apparently eoip adds an overhead of 42 bytes, so it should fit ok.

Re: EoIP: guarantee MTU of 1500

Posted: Fri Dec 08, 2023 6:42 am
by Amm0
What is the best approach to guarantee MTU of 1500 without fragmentation? Am I out of luck until Mikrotik fixes the wifiwave2 bug that limited L2 MTU of the wireless interfaces to 1560?
FWIW, the current stable RouterOS allows MTU of 2290 with wifiwave2 (renamed wifi-qcom-XXX in 7.13). But there totally was a bug that 1500 was the L2MTU in wifiwave2 — even though it allow setting higher. See viewtopic.php?t=180369&hilit=MTU

But EoIP MTU would have gotten crushed over wifiwave2 until a few months ago... but shouldn't in recent builds.

Re: EoIP: guarantee MTU of 1500

Posted: Fri Dec 08, 2023 8:18 am
by Kentzo
FWIW, the current stable RouterOS allows MTU of 2290 with wifiwave2.

Hmm, I get the out-of-range error on AX3 with 7.12.1 when I attempt to set a value greater than 1560.

Re: EoIP: guarantee MTU of 1500

Posted: Fri Dec 08, 2023 9:28 am
by Amm0
FWIW, the current stable RouterOS allows MTU of 2290 with wifiwave2.
Hmm, I get the out-of-range error on AX3 with 7.12.1 when I attempt to set a value greater than 1560.

Opps, I guess I meant the previous stable. There is a new bug in 7.12, so they limit to 1560. From 7.12.1 changelog:
limit L2MTU to 1560 until a fix is available for a bug causing interfaces to fail transmitting larger frames than that;