Allied Telesis SwitchBlade x3100 Series Manual page 444

Introduction
The Enhanced Recovery feature changes the processing of this condition in both the Master and Transit nodes
so that some additional network connectivity can be restored when one or more links in a multiple-link failure
are restored, and there is still at least one link that has not been restored.
When the Master and Transit nodes are operating in Enhanced EPSR mode, a Transit node that has recovered
its failed ring port and has its other port in a non-failed state will send a message (called a Link-Forward-
Request message or LFR message) to the Master node that it has recovered its failed port. When the Master
node receives this message, it starts a Link-Forward-Request-Process timer, or LFRP timer (fixed at 4 sec-
onds). If the timer expires and the Master node has not been able to recover the ring from the multiple-link fail-
ure, the Master mode sends a message back to this Transit node that it can safely restore traffic on its
recovered link.
If the Transit node has both ring ports in a failed state and one port recovers, the Transit can safely
Note:
enable traffic on the one recovered port since it knows the ring is not yet a loop because of the other
port's failed state.
If the multiple link failure condition is resolved and the Master Node is able to restore the normal ring before
the 4-second LFRP timer expires, it sends out its normal "Ring-Up-Flush-FDB" message, and the recovery pro-
cedure described in 4.6.4.6
When the Transit node sends the LFR message asking if it can recover traffic on its restored link, it also starts
an LFR timing interval (fixed at 6 seconds). If this timer expires and the Transit node has received from the
Master Node neither a message that it can recover its failed link nor a Ring-Up-Flush-FDB message, it will
resend the message asking that it restore message to its recovered link.
The scenario described above is labeled EPSR+, and it assumes that there is communication between
Note:
the Transit node with the recovered port and the Master node.
It is also possible that the Master node may be in a failed state or is unreachable. In this scenario, when the
Transit node resends the LFR message asking that it restore its recovered link and does not receive a response,
the Transit node will go ahead and begin traffic on its recovered port.
This scenario, in which the Transit Node cannot communicate with the Master node and still begins
Note:
traffic on its recovered port, is labeled EPSR++.
The Transit node will continue to pass traffic over its recovered ports until communication with the Master
node is restored. At this point, the Master node will send out its normal "Ring-Up-Flush-FDB" message, and
the recovery procedure described in
This feature is activated with the parameter
CREATE EPSR MASTER |
The
ENHANCEDRECOVERY
4-124
Software Reference for SwitchBlade x3100 Series Switches (Layer Two Switching)
is followed.
4.6.4.6 is followed.
ENHANCEDRECOVERY
TRANSIT.
parameter is also added to the
EPSR+ and EPSR++ (Multiple Link Failure)
, that is added to the existing EPSR command
SET EPSR and SETDEFAULTS EPSR.