Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 1500)

EPSR Introduction and Configuration
Software Reference for x310 Series Switches
57.18 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Figure 57-11: EPSR Superloop data path caused by a broken common ring segment
EPSR Superloop Prevention
Alliedware Plus version 5.4.2 onwards contains mechanisms to prevent superloops
forming. The Superloop prevention facility enables rings to be assigned priority level
between 0 and 127, with 1 representing the lowest priority and 127 the highest. Level 0
(the default setting) applies the functionality of no Superloop prevention. Enabling
superloop prevention changes the way the EPSR nodes respond under fault conditions.
Superloop prevention is enabled for an EPSR ring instance by setting the epsr priority
command on page 58.7 . Setting a priority value greater than 0 applies superloop
prevention to that particular instance. How the superloop function is applied will depend
on the role of the node within the ring, i.e. whether it is a master node or a transit node,
and its physical location within the ring. Here is how the functions of Superloop
prevention modify the nodal behavior for a particular ring instance:
■ A master node with its epsr priority set to zero will consider the superloop function to
be turned off.
■ A master node with its epsr priority set within the range 1-127 will consider the
superloop function to be enabled, and will change its behavior in the following ways.
« It will not unblock its secondary port following the expiry of the Master Node
Hello message timer. However, a ring-down-flush message will still be sent.
« It will only unblock its secondary port when it receives a Links Down message
from a transit node.
■ A transit node that is not connect to a shared link will be unaffected by having its epsr
priority set for any of its instances.
EPSR_SLoopPath.eps
Data Path
Superloop