User guide

Serial-Cable Failover
ExtremeWarePx1 1.2 Command Reference Guide 167
from the master to the backup, replacing the corresponding commands on the backup. After all the
commands have been replaced, the conÞguration is saved and the backup switch is rebooted.
¥ Whenever a relevant conÞguration command is issued on the master switch, the command is
automatically send to the backup switch, where it is stored in local memory. When a build
command is issued on the master switch, the backup executes the stored commands in sequence and
issues its own build command. The backup switch does not save the result. If you do not explicitly
issue the save configuration command on the backup switch before the next boot, the
conÞguration is lost.
Serial-Cable Failover
Serial-cable failover provides faster (sub-second) failover between the VRRP peers. When this feature is
enabled, in addition to sending and receiving VRRP advertisements via the Gigabit port, the VRRP
peers also exchange heartbeat messages by using the second serial port on each switch. A null-modem
serial cable is used. If the either switch does not receive heartbeats from its VRRP peer, it initiates a
failover. The failover latency is currently set to approximately one second.
The heartbeat interval property controls the frequency at which the switch sends heartbeat messages.
The lower the value, the faster failover occurs when the active switch goes down. The default value for
this property is 500 millisecond. The value can be changed with the
configure vrrp serial-failover
interval
command.
If you enable serial-cable failover on one switch and do not enable serial-cable failover on its VRRP
peer, there will be a temporary glitch because all the VRRP classes will attempt to become active on the
switch where serial-cable failover is enabled. This is an install issue when serial-cable failover is Þrst
enabled. The following messages that will be logged when VRRP serial-cable failover is deployed:
00:03:56 0 days:INFO: Enable VRRP serial failover
00:03:56 0 days:INFO: Disable VRRP serial failover
00:03:56 0 days:INFO:VRRP serial cable CTS asserted
00:03:56 0 days:INFO:VRRP serial cable CTS desserted
00:01:43 0 days:WARNING:VRRP serial heartbeats from peer missing!
00:01:55 0 days:WARNING:Received serial cable heartbeat msg when serial failover is
not enabled!"
These messages may be logged whenever you change the conÞguration of VRRP serial-cable failover, or
in response to changes on the serial link that joins the two VRRP peers.
Server-Health Failover
You can conÞgure an application switch so that one of the failover criteria for a VRRP class is the
number of servers in that class that are down (as per health check) on the other switch. To use this
feature for a particular class, you issue the configure vrrp add track-servers-delta command. This
command speciÞes a limit on the difference between the number of servers for that class on the two
switches. The backup switch attempts to become active if sees that many more servers than the other
switch sees.
The limit for each VRRP class must conÞgured the same on both switches.