Specifications

236 ExtremeWare XOS 11.0 Concepts Guide
Extreme Standby Router Protocol
Electing the Master Switch
A new master can be elected in one of the following ways:
• A communicated parameter change
• Loss of communication between master and slave(s)
If a parameter determines the master changes (for example, link loss or priority change), the election of
the new master typically occurs within one second. A parameter change triggers a handshake between
the routers. As long as both routers agree upon the state transition, new master election is immediate.
If a switch in slave mode loses its connection with the master, a new election (using the same
precedence order indicated on page 234 or using a configured precedence order described in “ESRP
Election Algorithms” on page 237) occurs. The new election typically takes place in three times the
defined timer cycle (8 seconds by default).
Before the switch transitions to the master state, it enters a temporary pre-master state. While in the
pre-master state, the switch sends ESRP PDUs until the pre-master state timeout expires. Depending
upon the election algorithm, the switch may then enter the master or slave state. Traffic is unaffected by
the pre-master state because the master continues to operate normally. The pre-master state avoids the
possibility of having simultaneous masters.
You can configure the pre-master state timeout using the following command:
configure esrp <esrpDomain> timer premaster <seconds>
CAUTION
Configure the pre-master state timeout only with guidance from Extreme Networks personnel.
Misconfiguration can severely degrade the performance of ESRP and your switch.
ESRP Failover Time
ESRP Failover time is largely determined by the following factors:
• ESRP hello timer setting.
• ESRP neighbor timer setting.
• The routing protocol being used for interrouter connectivity if Layer 3 redundancy is used; OSPF
failover time is faster than RIP failover time.
The failover time associated with the ESRP protocol depends on the timer setting and the nature of the
failure. The default hello timer setting is 2 seconds; the range is 2 to 1024 seconds. The default neighbor
timer setting is 8 seconds; the range is 3*hello to 1024 seconds. The failover time depends on the type of
event that caused ESRP to failover. In most cases, a non-hardware failover is less than 1 second, and a
hardware failover is 8 seconds.
If routing is configured, the failover of the particular routing protocol (such as RIP V1, RIP V2, or OSPF)
is added to the failover time associated with ESRP.
If you use OSPF, make your OSPF configuration passive. A passive configuration acts as a stub area and
helps increase the time it takes for recalculating the network. A passive configuration also maintains a
stable OSPF core.