TMS zl Management and Configuration Guide ST.1.0.090213

8-6
High Availability
Overview
has gone offline, so it assumes the role of master and begins to transmit
gratuitous ARP messages over the network to associate the cluster’s IP
addresses with the participant’s MAC addresses. In the meantime, the master
continues to respond to ARP requests by associating its MAC addresses with
the cluster’s IP addresses.
This situation is called a “split brain” situation because both modules are
attempting to perform the same function using the same IP addresses and yet
cannot detect each other. To prevent a split-brain situation, install redundant
links between the host switches.
If one or more failed links result in a split-brain situation and the link is later
restored, the cluster reforms. The master will be the module that was the
master before the link failed.
You will also create a split-brain situation by deleting the HA VLAN on one
switch only. (When you delete an HA VLAN from the host switch, the HA traffic
moves onto the default VLAN without an interruption in traffic.)
HA, Traffic Types, and Settings
Table 8-1 shows how HA clusters deal with different types of traffic and
module settings.
Table 8-1. Synchronization and Failover in HA Clusters
Synchronized Fails Over
• current startup-config
• static routing table
• IDS/IPS signatures
• TCP connections
• UDP connections
•NAT
• IPsec VPNs (except L2TP over IPsec)
• GRE tunnels
•ALGs
• IDS/IPS signatures
Does Not Fail Over
• Connections to and from Self
• multicast traffic
• broadcast traffic
• ICMP traffic
• L2TP over IPsec VPNs
• rate limiting
• PPP connections
• IDS/IPS subscription