Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 335)

Brocade Virtual ADX Server Load Balancing Guide 319
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Configuring the forwarding of synchronizing messages
6
Configuring the forwarding of synchronizing messages
In a Hot Standby HA configuration, the active Brocade Virtual ADX and the backup Brocade Virtual
ADX continuously communicate through synchronizing messages. These messages contain Layer 4
–Layer 7 session status information and are only used by the Brocade Virtual ADX devices.
Some of the messages can travel over a non-dedicated private link between the two Brocade
Virtual ADX devices. Another Brocade Virtual ADX can be in the middle of this link, acting as a Layer
2 or Layer 3 Switch passing traffic between the active and backup Brocade Virtual ADX devices.
In this situation, messages sent between the active and backup Brocade Virtual ADX devices can
be intercepted and dropped by the Brocade Virtual ADX in the middle, and not forwarded to the
active or backup Brocade Virtual ADX devices. This could cause loss of synch between the active
and backup Brocade Virtual ADX devices. To prevent this from happening, use the server
fwd-l4-sync command to configure the Brocade Virtual ADX in the middle to simply forward the
synching messages and not intercept them.
To configure the Brocade Virtual ADX in the middle to forward the synchronizing messages, enter
the following command on the Brocade Virtual ADX connecting the active and the backup Brocade
Virtual ADX devices.
Virtual ADX(config)#server fwd-l4-sync
Syntax: server fwd-l4-sync
Configuring synchronization with HA
You can use the config-sync command line utility to synchronize an SLB configuration from the
active Brocade Virtual ADX to the standby Brocade Virtual ADX. For information about the
config-sync command, refer to the "Initiating the Synchronization" section of the "Brocade Virtual
ADX System Management" chapter in the Brocade Virtual ADX Administration Guide.
Hot-standby HA with routing protocols
When the upstream and the downstream routers are on the different VLANs, the routing protocols
like OSPF and BGP should be up and running on both active and standby devices in addition to
static routes. Brocade Virtual ADX learns the routes advertised by the routing protocol as well as
the static routes configured. As soon as a device becomes active, the new active starts allowing the
packets for forwarding. In contrast, though the same learnt and configured routes are present on
the standby device, it does not forward the packets.
With the routing protocols configured, both active and standby devices advertise the routes to the
upstream and downstream routers, including the VIP RHI routes. However Brocade Virtual ADX
automatically adjusts the cost of the advertised routes without any additional configuration,
ensuring that the traffic is always targeted to the active device. This cost alteration by the system is
not be reflected in the running configuration of the Brocade Virtual ADX.