Unifi Security Gateway MTU & MSS Clamping

Unifi Security Gateway MTU & MSS Clamping

Here is how to possibly fix a Unifi Security Gateways to work on a PPPOE connection.

On the Unifi controller, set the security gateway to enable “MSS clamping” and set the size of clamping at a custom size of “1406”.
If that alone does not fix the problem, you might need to also set the MTU size to 1480

Unfortunately this can not be done from the GUI and will need to be performed through CLI. SSH onto the gateway and running:

configure
set interfaces ethernet eth0 pppoe 0 mtu 1480
commit

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