Virtual Private LAN Services
7750 SR OS Services Guide Page 643
feature provides an LDP-based mechanism for recovering a physical link failure in a dual-homed
connection to a VPLS service. This method provides an alternative to RSTP solutions where dual
homing redundancy and recovery, in the case of link failure, is resolved by RSTP running between a
PE router and CE devices. If the endpoint is configured within the VPLS and send-flush-on-failure is
enabled, flush-all-from-me messages will be sent out only when all spoke SDPs associated with the
endpoint go down.
This feature cannot be enabled on management VPLS.
Default no send-flush-on-failure
service-mtu
Syntax service-mtu octets
no service-mtu
Context config>service>vpls
Description This command configures the service payload (Maximum Transmission Unit – MTU), in bytes, for
the service. This MTU value overrides the service-type default MTU. The service-mtu defines the
payload capabilities of the service. It is used by the system to validate the SAP and SDP binding’s
operational state within the service.
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.
Default VPLS: 1514
The following table displays MTU values for specific VC types.
octets
VC-Type Example
Service MTU
Advertised
MTU
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