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Cisco ASDM User Guide
OL-16647-01
Chapter 34 IKE
Load Balancing
To implement load balancing, you group together logically two or more devices on the same private
LAN-to-LAN network into a virtual cluster.
All devices in the virtual cluster carry session loads. One device in the virtual cluster, the virtual cluster
master, directs incoming calls to the other devices, called secondary devices. The virtual cluster master
monitors all devices in the cluster, keeps track of how busy each is, and distributes the session load
accordingly. The role of virtual cluster master is not tied to a physical device; it can shift among devices.
For example, if the current virtual cluster master fails, one of the secondary devices in the cluster takes
over that role and immediately becomes the new virtual cluster master.
The virtual cluster appears to outside clients as a single virtual cluster IP address. This IP address is not
tied to a specific physical device. It belongs to the current virtual cluster master; hence, it is virtual. A
VPN client attempting to establish a connection connects first to this virtual cluster IP address. The
virtual cluster master then sends back to the client the public IP address of the least-loaded available host
in the cluster. In a second transaction (transparent to the user) the client connects directly to that host.
In this way, the virtual cluster master directs traffic evenly and efficiently across resources.
Note All clients other than the Cisco VPN client, the Cisco VPN 3002 Hardware Client, or the ASA 5505
operating as an Easy VPN Client connect directly to the security appliance as usual; they do not use the
virtual cluster IP address.
If a machine in the cluster fails, the terminated sessions can immediately reconnect to the virtual cluster
IP address. The virtual cluster master then directs these connections to another active device in the
cluster. Should the virtual cluster master itself fail, a secondary device in the cluster immediately and
automatically takes over as the new virtual session master. Even if several devices in the cluster fail,
users can continue to connect to the cluster as long as any one device in the cluster is up and available.
Prerequisites
Load balancing is disabled by default. You must explicitly enable load balancing.
You must have first configured the public and private interfaces and also have previously configured the
the interface to which the virtual cluster IP address refers.
All devices that participate in a cluster must share the same cluster-specific values: IP address,
encryption settings, encryption key, and port. All of the outside and inside network interfaces on the
load-balancing devices in a cluster must be on the same IP network.
Fields
• VPN Load Balancing—Configures virtual cluster device parameters.
–
Participate in Load Balancing Cluster—Specifies that this device is a participant in the
load-balancing cluster.
–
VPN Cluster Configuration—Configures device parameters that must be the same for the
entire virtual cluster. All servers in the cluster must have an identical cluster configuration.
–
Cluster IP Address—Specifies the single IP address that represents the entire virtual cluster.
Choose an IP address that is within the public subnet address range shared by all the security
appliances in the virtual cluster.
–
UDP Port—Specifies the UDP port for the virtual cluster in which this device is participating.
The default value is 9023. If another application is using this port, enter the UDP destination
port number you want to use for load balancing.