How Ring Breaks Are Detected And Healed - HP ProCurve 9304M Installation And Configuration Manual

Installation and Basic Configuration Guide
• 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 10.4 shows an example.
Figure 10.4 Metro ring – from Preforwarding to Forwarding
PF
F
Customer A
PF
Each RHP also has a sequence number. MRP can use the sequence number to determine the round-trip time for
RHPs in the ring. See "Using MRP Diagnostics" on page 10-12.

How Ring Breaks Are Detected and Healed

Figure 10.5 shows ring interface states following a link break. MRP quickly heals the ring and preserves
connectivity among the customer networks.
10 - 8
Customer A
F
PF F
Switch B
Secondary port
receives RHP 1
and changes to
Blocking
Switch C
Primary port then
sends RHP 2 with
forwarding bit on
Switch D
PF
PF
F
Customer A
RHP 2
Forwarding bit is on.
Each port changes from
Preforwarding to Forwarding
when it receives this RHP.
F
F
Switch A Master
Node
Customer A
B