Virtual Private LAN Services
7210 SAS-X, R6 OS Services Guide Page 373
The service MTU and a SAP’s service delineation encapsulation overhead (i.e., 4 bytes for a dot1q
tag) is used to derive the required MTU of the physical port or channel on which the SAP was created.
If the required payload is larger than the port or channel MTU, then the SAP will be placed in an
inoperative state. If the required MTU is equal to or less than the port or channel MTU, the SAP will
be able to transition to the operative state.
When binding an SDP to a service, the service MTU is compared to the path MTU associated with the
SDP. The path MTU can be administratively defined in the context of the SDP. The default or
administrative path MTU can be dynamically reduced due to the MTU capabilities discovered by the
tunneling mechanism of the SDP or the egress interface MTU capabilities based on the next hop in
the tunnel path. If the service MTU is larger than the path MTU, the SDP binding for the service will
be placed in an inoperative state. If the service MTU is equal to or less than the path MTU, then the
SDP binding will be placed in an operational state.
In the event that a service MTU, port or channel MTU, or path MTU is dynamically or
administratively modified, then all associated SAP and SDP binding operational states are
automatically re-evaluated.
For i-VPLS and EPIPEs bound to a b-VPLS, the service-mtu must be at least 18 bytes smaller than
the b-VPLS service MTU to accomodate the PBB header.
The no form of this command returns the default service-mtu for the indicated service type to the
default value.
Note: To disable service MTU check execute the command no service-mtu-check. Disabling service
MTU check allows the packets to pass to the egress if the packet length is lesser than or equal to the
MTU configured on the port.
Default VPLS: 1514
The following table displays MTU values for specific VC types.
octets
The size of the MTU in octets, expressed as a decimal integer.
Values 1 — 9194
service-mtu-check
Syntax [no] service-mtu-check
Context config>service>vpls
VC-Type Example
Service MTU
Advertised
MTU
Ethernet 1514 1500
Ethernet (with preserved dot1q) 1518 1504
VPLS 1514 1500
VPLS (with preserved dot1q) 1518 1504
VLAN (dot1p transparent to MTU value) 1514 1500
VLAN (QinQ with preserved bottom Qtag) 1518 1504
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