HP ProCurve 9304M Installation And Configuration Manual page 303

Figure 10.3 Metro ring – initial state
PF
F
Customer A
PF
MRP uses Ring Health Packets (RHPs) to monitor the health of the ring. An RHP is an MRP protocol packet. The
source address is the MAC address of the master node and the destination MAC address is a protocol address for
MRP. The Master node generates RHPs and sends them on the ring. The state of a ring port depends on the
RHPs.
A ring interface can have one of the following MRP states:
• Preforwarding (PF) – The interface can forward RHPS but cannot forward data. All ring ports being in this
state when you enable MRP.
• Forwarding (F) – The interface can forward data as well as RHPs. An interface changes from Preforwarding
to Forwarding when one of the following occurs:
• The port receives an RHP with its forwarding bit on. The forwarding bit, when set to 1 (on), instructs the
receiving port to immediately change its state from Preforwarding to Forwarding. This occurs during ring
initialization.
• The port's preforwarding time expires. This occurs if the port does not receive an RHP from the Master,
or if the forwarding bit in the RHPs received by the port is off. This indicates a break in the ring. The port
heals the ring by changing its state to Forwarding. The preforwarding time is the number of milliseconds
the port will remain in the Preforwarding state before changing to the Forwarding state, even without
receiving an RHP.
• Blocking (B) – The interface cannot forward data. Only the secondary interface on the Master node can be
Blocking. An RHP's forwarding bit cannot change this interfaces's state to Forwarding. Instead, the
forwarding bit sets this interface to Blocking, to break the forwarding loop in an intact ring.
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.
Customer A
F
PF PF
Switch B
All ports start in
Preforwarding state.
Switch C
Primary port on Master
node sends RHP 1
Switch D
PF
PF
F
Customer A
Configuring Metro Features
PF
F
Switch A Master
Node
Customer A
P F
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