Dell PowerConnect B-RX Configuration Manual page 481

When MRP is enabled, all ports begin in the Preforwarding state. The primary interface on the
Master node, although it is in the Preforwarding state like the other ports, immediately sends an
RHP onto the ring. The secondary port on the Master node listens for the RHP.
•
•
Figure 66
FIGURE 66
Each RHP also has a sequence number. MRP can use the sequence number to determine the
round-trip time for RHPs in the ring. Refer to
BigIron RX Series Configuration Guide
53-1002253-01
If the secondary port receives the RHP, all links in the ring are up and the port changes its state
to Blocking. The primary port then sends another MRP with its forwarding bit set on. As each
of the member ports receives the RHP, the ports changes their state to Forwarding. Typically,
this occurs in sub-second time. The ring very quickly enters the fully initialized state.
If the secondary port does not receive the RHP by the time the preforwarding time expires, a
break has occurred in the ring. The port changes its state to Forwarding. The member ports
also change their states from Preforwarding to Forwarding as their preforwarding timers expire.
The ring is not intact, but data can still travel among the nodes using the links that are up.
shows an example.
Metro ring – from Preforwarding to Forwarding
PF
F
Switch C
Customer A
PF
Customer A
F
PF F
Switch B
Secondary port
receives RHP 1
and changes to
Blocking
Primary port then
sends RHP 2 with
forwarding bit on
Switch D
PF
PF
F
Customer A
"MRP phase 2"
Ring initialization
RHP 2
Forwarding bit is on.
Each port changes from
Preforwarding to Forwarding
when it receives this RHP.
F
F
Master
Switch A
Node
Customer A
B
on page 412.
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