ServerIron ADX Server Load Balancing Guide
Release 12.0.00
June 15, 2009

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Server Load Balancing > Symmetric SLB

Symmetric SLB
Symmetric Server Load Balancing (SLB) allows you to use multiple ServerIron ADXs to simultaneously load balance VIP traffic and provide hot standbys for one another’s VIPs. In addition to their roles as mutual backups, each ServerIron ADX actively provides Layer 4 SLB (and TCS, if configured) services. As a result, you get the fault protection of a hot standby configuration while doubling connection capacity.
In a Symmetric SLB configuration, each VIP is actively served by only one of the ServerIron ADXs. The other ServerIron ADXs are standbys for that VIP, although they may each simultaneously be the active ServerIron ADX for other VIPs. You determine which ServerIron ADX is the active ServerIron ADX for a VIP by assigning a priority to each VIP. The ServerIron ADX that has the highest priority for a specific VIP is the active ServerIron ADX for the VIP by default. The other ServerIron ADXs have lower priorities for the VIP and are standbys for that VIP. Only if the ServerIron ADX that has the highest priority for the VIP becomes unavailable does another ServerIron ADX (with the next highest priority for the VIP) assume service for the VIP.
To configure Symmetric SLB, you configure the same VIPs on multiple ServerIron ADXs that have Layer 2 connectivity, then assign a different SLB priority to each VIP on each of the ServerIron ADXs. For example, to configure two ServerIron ADXs for SLB, configure the same VIPs on each of the ServerIron ADXs. On one of the ServerIron ADXs, assign half of the VIPs a priority of 1 (lowest) and assign the other VIPs a priority of 255 (highest). Assign the reverse priorities to the VIPs on the other ServerIron ADX.
A typical Symmetric SLB configuration uses a redundant set of real servers connected to each ServerIron ADX. The VIPs and their contents are identical on each pair of servers. The only difference for each VIP is the priority you assign the VIP on a particular virtual server. You can configure a priority from 1 – 255 and you can use up to 255 ServerIron ADXs in a Symmetric SLB configuration.
NOTE: You need to enable VRRP or VRRP-E on ServerIron ADXs that are in a Symmetric SLB configuration; otherwise, FTP, RTSP, and MMS protocols may not work. Also, configure the IP address of the real server’s default gateway as the VRID of the VRRP or VRRP-E.
Figure 2.3 shows an example of Symmetric SLB.
Figure 2.3
Link-Level Redundancy
Symmetric SLB includes link-level redundancy to provide fault tolerance against failed links.
If a link from a ServerIron ADX to the real servers fails, Symmetric SLB can use an alternate path through another ServerIron ADX running Symmetric SLB to reach the real servers. Link-level redundancy requires no additional configuration. If the ServerIron ADXs have Layer 2 connectivity and you configure Symmetric SLB priorities for the VIPs, then link-level redundancy is automatically enabled.
See “Symmetric SLB”.

Server Load Balancing > Symmetric SLB

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