Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 1499)

EPSR Introduction and Configuration
Software Reference for x310 Series Switches
C613-50046-01 REV A AlliedWare Plus TM Operating System - Version 5.4.4C 57.17
Superloop Protection
Careful attention must be paid when creating EPSR networks with interconnecting links,
to avoid an error condition known as superloops. This sections explains what superloops
are and how to prevent them.
What is an EPSR Superloop?
An EPSR superloop is a data loop whose path traverses more than a single EPSR ring. This
fault condition usually occurs when there is a break in a physical segment that is shared by
the two rings. For a superloop condition to occur, the two physical rings must share some
of their data VLANS.
Figure 57-10 on page 57.17 shows an EPSR ring with a superloop
condition caused by a break in the common ring segment. Figure 57-11 on page 57.18
shows the Superloop data path ring caused by the broken common ring segment. The
superloop condition occurs because both rings detect the ring segment break and as a
result both master nodes unblock their secondary ports.
Figure 57-10: Interconnected EPSR Rings with Data VLAN Sharing
EPSR_SLoop.eps
Transit
Node
Transit
Node
Transit
Node E
Transit
Node
Primary
Port Secondary
Port
Transit
Node
Master
Node
Master
Node
Transit
Node D
Port
Unblocks
Same Data VLAN
Control VLAN
Control VLAN
Primary
Port
Secondary
Port
Common
Segment
(Broken)
Port
Unblocks
Ring One
Ring Two
Control VLAN (Ring One)
Data VLAN (Ring One and Ring Two)
Control VLAN (Ring Two)