VPLS service MTU is supported on all 7210 SAS platforms as described in this document, except the 7210 SAS-T operating in access-uplink mode.
The user must ensure that the port MTU is configured appropriately so that the largest packet traversing through any of the SAPs (virtual ports) of the VPLS service can be forwarded out of any of the SAPs. VPLS services do not support fragmentation and can discard packets larger than the configured port MTU.
When an IP interface is associated with a VPLS service, the IP-MTU is based on either the administrative value configured for the IP interface or an operational value derived from port MTU of all the SAPs configured in the service. The port MTU excluding the Layer 2 Header and tags for all the ports which have SAPs configured in this VPLS service are considered and the minimum value among those are computed (which is called computed MTU). The operational value of the IP interface is set as follows:
If the configured (administrative) value of IP MTU is greater than the computed MTU, then the operational IP MTU is set to the computed MTU.
If the configured (administrative) value of IP MTU is lesser than or equal to the computed MTU, then operational IP MTU is set to the configured (administrative) value of IP MTU.