Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 531)

Multi-Service IronWare Switching Configuration Guide 501
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Tuning MRP timers
14
Hello time
This timer specifies the interval at which RHP’s are generated by the ring master. It should be noted
that this interval is applied not only to standard RHP’s but also to topology change notification
RHP’s. For example: Setting the hello time to its maximum value of 15,000 ms would mean that
the three topology change notification RHP’s that are sent following a ring break being detected or
a ring heal event would result in MAC table flushes three times at 15 second intervals. On a busy
network this would cause unnecessary impact.
Preforwarding time
The preforwarding time defines the amount of time an interface will take to move from blocking to
preforwarding without RHP’s being received. It also defines the amount of time an interface will
take to move from preforwarding to forwarding without RHP’s being received.
The preforwarding time must be at least 2 x hello time and must be a multiple of the hello time.
The preforwarding time for a lower priority ring must be greater than or equal to the highest higher
priority ring.
For example: Setting the preforwarding time to its maximum value of 30,000 ms will mean that a
break in the ring (assuming no alarm RHP’s are generated) will take one minute to heal.
Setting hello and preforwarding timers appropriately
When setting timers both the hello time and the preforwarding time should be considered to
ensure that the appropriate recovery time is applied on the network.
Consider a break in the network that does not generate alarm RHP’s
Example 1(default values):
Preforwarding time = 300ms
Hello time = 100ms
Time to forwarding = 2 x preforwarding time = 600ms
Post recovery mac table flush time = 3 x hello time = 300ms
Full connectivity = Time to forwarding + Post recovery mac table flush time = 900ms = 0.9secs
Example 2:
Preforwarding time = 10000ms
Hello time = 100ms
Time to forwarding = 2 x preforwarding time = 20000ms
Post recovery mac table flush time = 3 x hello time = 300ms
Full connectivity = Time to forwarding + Post recovery mac table flush time = 20300ms = 20.3secs