Dell PowerConnect B-RX BigIron RX Series Configuration Guide v02.7.03 - Page 469

Ring initialization 14 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 66 shows an example. FIGURE 66 Metro ring - from Preforwarding to Forwarding Customer A F PF F Switch B RHP 2 Forwarding bit is on. Each port changes from Preforwarding to Forwarding when it receives this RHP. PF F Customer A PF Switch C Secondary port receives RHP 1 and changes to Blocking Primary port then sends RHP 2 with forwarding bit on F Switch A Master Node B F Customer A Switch D PF PF F Customer A 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 "MRP phase 2" on page 404. BigIron RX Series Configuration Guide 397 53-1001986-01