Alcatel-Lucent 7210 SAS M Service Manual page 148

Pseudowire Switching
Master-slave pseudowire redundancy adds the ability for the remote peer to react to the
pseudowire standby status notification, even if only one spoke SDP terminates on the VLL
endpoint on the remote peer. When the CLI command standby-signaling-slave is enabled at the
spoke SDP or explicit endpoint level in PE2 and PE3, then any spoke SDP for which the remote
peer signals PW FWD Standby will be blocked in the transmit direction.
This is achieved as follows. The standby-signaling-master state is activated on the VLL endpoint
in PE1. In this case, a spoke SDP is blocked in the transmit direction at this master endpoint if it is
either in operDown state, or it has lower precedence than the highest precedence spoke SDP, or the
given peer PE signals one of the following pseudowire status bits:
•
•
•
•
•
The fact that the given spoke SDP has been blocked will be signaled to LDP peer through the
pseudowire status bit (PW FWD Standby (0x20)). This will prevent traffic being sent over this
spoke SDP by the remote peer, but obviously only in case that remote peer supports and reacts to
pseudowire status notification. Previously, this applied only if the spoke SDP terminates on an
IES, VPRN or VPLS. However, if standby-signaling-slave is enabled at the remote VLL endpoint
then the Tx direction of the spoke SDP will also be blocked, according to the rules in
Master-Slave Pseudowire Redundancy with Existing Scenarios on page
Note that although master-slave operation provides bidirectional blocking of a standby spoke SDP
during steady-state conditions, it is possible that the Tx directions of more than one slave endpoint
can be active for transient periods during a fail-over operation. This is due to slave endpoints
transitioning a spoke SDP from standby to active receiving and/or processing a pseudowire
preferential forwarding status message before those transitioning a spoke SDP to standby. This
transient condition is most likely when a forced switch-over is performed, or the relative
preferences of the spoke SDPs is changed, or the active spoke SDP is shutdown at the master
endpoint. During this period, loops of unknown traffic may be observed. Fail-overs due to
common network faults that can occur during normal operation, a failure of connectivity on the
path of the spoke SDP or the SAP, would not result in such loops in the data path.
Local Rules at Slave VLL PE
It must not be possible to configure standby-signaling-slave on endpoints or spoke SDPs bound to
an IES, VPRN, ICB, MC-EP or that form part of an MC-LAG or MC-APS.
If 'standby-signaling-slave' is configured on a given spoke SDP or explicit endpoint, then the
following rules apply. Note that the rules describe the case of several spoke SDPs in an explicit
endpoint. The same rules apply to the case of a single spoke SDP outside of an endpoint where no
endpoint exists:
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Pseudowire not forwarding (0x01)
SAP (ingress) receive fault (0x02)
SAP (egress) transmit fault (0x04)
SDP binding (ingress) receive fault (0x08)
SDP binding (egress) transmit fault (0x10)
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7210 SAS M Services Guide
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