Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 511)

Multi-Service IronWare Switching Configuration Guide 481
53-1003036-02
How ring breaks are detected and healed
14
• 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 109 .
• Forwarding interfaces – All member interfaces remain in the forwarding state unless the
physical interface is in an error condition.
When the link is repaired, the associated MRP interfaces come up in the preforwarding state
allowing RHPs to be forwarded around the ring and finally 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.
MRP alarm RHP enhancement
Prior to the enhancement detection of ring breaks were completely timer based. If the ring master
fails to receive RHPs for a period of 3 “hello times” (by default the hello time is 100 ms) this
indicates that the ring is broken in some manner. This initiates a topology change as described in
the previous section. The convergence time associated with such an event could take several
hundred milliseconds.
This enhancement enables ring nodes to rapidly notify the master of link failures. To understand
the mechanism we introduce the concept of downstream switches in the ring and how member
switches determine the primary and secondary ring interfaces. Remember that a primary ring
interface sends RHPs and a secondary ring interface receives RHPs.
To fully understand the mechanism the reader needs to be aware of the concept of shared
interfaces and interface owner ID’s which are a function of MRP phase 2.
A downstream switch is defined as the next switch that will receive the ring RHP originated from the
master primary interface for a particular ring. In
Figure 110 Switch B is downstream from the
master, Switch C is downstream from Switch B and so on and so forth. In addition it should be
noted that a member switch identifies which ring interface is secondary for each discrete ring by
virtue of the receipt of RHPs for that ring. In a topology with shared interfaces a single physical
interface can therefore be a primary ring interface for one ring and a secondary ring interface for
another ring. It should be noted that the output of the ‘show metro’ command as well as the
configuration will change if the primary and secondary ring interfaces of the master are swapped.
This keeps the identification of interface roles consistent with the flow of RHPs for discrete ring
instances.
When a link is detected to be down on a member switch secondary ring interface due to a link
failure an alarm RHP, which is an RHP with the alarm bit set, is sent from the primary ring interface
towards the ring master, notifying the master of the failure.
The destination MAC address in the alarm is the ring MAC address. The MAC address will be in the
format 0304.8000.00xx where ‘xx’ is the ring number in hexadecimal.
For example ring 100 = 0304.8000.0064. This ensures that the packet is hardware forwarded all
the way to the master. When the master in the ring receives this alarm the secondary interface is
immediately transitioned from blocking to forwarding.