Configuring Metro Features
December 2005 © Foundry Networks, Inc. 8 - 9
Figure 8.5 Metro ring – ring break
If a break in the ring occurs, MRP heals the ring by changing the states of some of the ring interfaces.
• Blocking interface – The Blocking interface on the Master node has a dead timer. If the dead time expires
before the interface receives one of its ring’s RHPs, the interface changes state to Preforwarding. Once the
secondary interface changes state to Preforwarding:
• If the interface receives an RHP, the interface changes back to the Blocking state and resets the dead
timer.
• If the interface does not receive an RHP for its ring before the Preforwarding time expires, the interface
changes to the Forwarding state, as shown in Figure 8.5.
• Forwarding interfaces – Each member interface remains in the Forwarding state.
When the broken link is repaired, the link’s interfaces come up in the Preforwarding state, which allows RHPs to
travel through the restored interfaces and reach the secondary interface on the Master node.
• If an RHP reaches the Master node’s secondary interface, the ring is intact. The secondary interface changes
to Blocking. The Master node sets the forwarding bit on in the next RHP. When the restored interfaces
receive this RHP, they immediately change state to Forwarding.
• If an RHP does not reach the Master node’s secondary interface, the ring is still broken. The Master node
does not send an RHP with the forwarding bit on. In this case, the restored interfaces remain in the
Preforwarding state until the preforwarding timer expires, then change to the Forwarding state.
Master VLANs and Customer VLANs
All the ring ports must be in the same VLAN. Placing the ring ports in the same VLAN provides Layer 2
connectivity for a given customer across the ring. Figure 8.6 shows an example.
F
F
F
Switch D
F
Customer A
F
F
F
F
F
Switch C
Switch A
Switch B
Master
Node
Customer ACustomer A
Customer A
F
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