Virtual Leased Line Services
7210 SAS M Services Guide Page 147
Master-Slave Operation
NOTE: 7210 SAS devices support only standby-signaling-master option. 7210 does not support
the CLI command standby-signaling-slave. In the discussion below, reference to standby-
signaling-slave command is only used to describe the solution. 7210 device can be used only
where standby-signaling-master is used in the example below.
This section describes master-slave operation for pseudowire redundancy, as well as the algorithm
used to select the active transmit object in a VLL endpoint.
Blocking the transmit direction of a VLL spoke SDP when the far-end PE signals standby are
covered in this section. A solution the Rx direction of standby spoke SDP at the master endpoint in
order to interoperate with PEs that play a slave role but do not support blocking the Tx direction
on receiving a standby. However, blocking Tx on standby is a feasible approach since blocking Tx
satisfies a majority of deployments.
Figure 24 illustrates the operation of master-slave pseudowire redundancy. In this scenario, an
Epipe service is provided between CE1 and CE2. CE2 is dual homed to PE2 and PE3, and thus
PE1 is dual-homed to PE2 and PE3 using Epipe spoke SDPs. The objectives of this feature is to
ensure that only one pseudowire is used for forwarding in both directions by PE1, PE2 and PE3 in
the absence of a native dual homing protocol between CE2 and PE2/PE3, such as MC-LAG. In
normal operating conditions (the SAPs on PE2 and PE3 towards CE2 are both up and there are no
defects on the ACs to CE2), PE2 and PE3 cannot choose which spoke SDP to forward on based on
the status of the AC redundancy protocol.
Figure 24: Master-Slave Pseudowire Redundancy
standby-signaling-master
PE1
PE3
PE2
A
S
L2 Switch
epipe
A
A
standby-signaling-slave
CE1
CE2
NO MC-LAG
Block
Fwd
epipe
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