Westermo RedFox Series - Manual (Page 307)

Westermo OS Management Guide
Version 4.17.0-0
14.1.1 FRNT introduction
The FRNT protocol handles fast reconfiguration in switched ring topologies. One
of the switches has the role of FRNT focal point while the other switches are
referred to as FRNT members. When the switches are connected in a ring, it is
the responsibility of the focal point to break the loop by putting one of its ports
(port ”M”) in blocking mode, see
fig. 14.1 .
Note
In an FRNT ring, only one of the switches can be configured as focal point.
The other switches should be configured as member switches (i.e., non-
”focal-point”).
Member
Focal
Point
Member Member
N N N N M M M M
Figure 14.1: FRNT network operating in ring mode. Port ”M” on the Focal Point is
in BLOCKING state.
Once a link failure is detected somewhere along the ring, the focal point will
put its blocked port (port ”M”) in forwarding mode to establish full connectivity
between the switches (see
fig. 14.2 ). FRNT is event based: switches detecting
a link down event will immediately send a link down FRNT message towards the
focal point. Intermediate switches will forward the FRNT messages with highest
priority, and the focal point will open its BLOCKED port (port ”M”) upon receiving
the link down message.
Link
break
Member
Focal
Point
Member Member
redundant path
Focal point opens
M N M M M N N N
Figure 14.2: FRNT network operating in bus mode due to broken link.
Similarly, when a broken link comes back up again and the ring is fully connected,
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