Brocade TurboIron 24X Series Configuration Guide - Manual (Page 317)

Brocade TurboIron 24X Series Configuration Guide 283
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Metro Ring Protocol (MRP)
RHP processing in MRP Phase 1
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
begin 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 the port 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.
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.
• 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.
Figure 12 shows an example.