Intel ER8100STUS - Express 8100 Router, Reference Manual

Page: 122 / 150

Reference.bok : Chapter10 110 Wed Apr 22 10:58:08 1998
110
Spanning Tree Algorithm
WAN Bridging Services
Bridging loop detection
and removal
Within the Spanning Tree Algorithm, bridges connected in a LAN must be capa-
ble of detecting potential “bridge loops”, and of removing these loops as they oc-
cur by blocking the appropriate links to other bridges. This is illustrated in the
following diagram:
An alternate path has been established by connecting Bridge B in parallel with
Bridges A and C, which also creates a potential bridging loop. However, by using
the Spanning Tree Algorithm, Bridge B breaks the loop by blocking its path to
segment 3.
Bridge failure
In the event that one of the bridges fails, the Spanning Tree Algorithm must be
capable of activating alternative paths.
Bridge A
Bridge C
Bridge B
Blocked by
Bridge B
#1
#3
#2
Matchbox Router
Matchbox Router
Matchbox Router
1045
Matchbox Router
Matchbox Router
Matchbox Router
Bridge A
Dropout
Bridge C
Bridge B
Activated
by Bridge B
#1
#3
#2
Matchbox Router
Matchbox Router
Matchbox Router
1046
Matchbox Router
Matchbox Router
Matchbox Router