HSRP and VRRP Optimization

Problem this snippet solves:

This iRule provides a manageable solution for load balancing to any number of any sized HSRP/VRRP groups of routers or firewalls. The problem is simple to understand (explained officially in Solution 9487) in that the individual HSRP/VRRP routers/firewalls in a group transmit packets using the hardware MAC address which is what populates the lasthop entry for those connections. The problem is that during an HSRP router failover all the currently open connections will have the lasthop MAC address set to the hardware MAC address of the failed router and will attempt to send the data related to those flows to that MAC address. This will cause all current connections to timeout and in general diminishes the value of HSRP/VRRP groups. The solution is to populate the lasthop entry for each new connection with the relevant virtual MAC address as opposed to the hardware MAC address. In this case the active router responding to the virtual MAC address will receive the traffic which is the correct solution.

Code :

## data-group ##
ltm data-group internal RouterA {
    records {
        00:17:0f:2a:10:4a {
            data "00:00:0C:07:AC:02 test"
        00:17:0f:17:cf:80 {
            data "00:00:0C:07:AC:04 test"
    type string
## iRule ##
  set entry [class lookup [format %s [LINK::lasthop]] RouterA]
  if { $entry ne "" } {
    lasthop [lindex $entry 1] [lindex $entry 0]

Tested this on version:

Published Jan 30, 2015
Version 1.0

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