Load balancing between two asterisk

I wants to create a load balancing service between two asterisk PBX servers to organize the registration of the extensions between these two servers ,

I have used zen software “www.zenloadbalancer.com” , but the extensions can’t register to the virtual IP,

I asked zen support team and they told me we include the maddr in the SIP header.

where we can put this parameter in asterisk?

Asterisk only appears to support incoming maddr parameters; it can’t originate them. You will need to modify the source code.

Load balancing and virtual machines doesn’t make much sense to me. If you have load problems, you need to be using real machines.

I would start by upgrading Asterisk, if you are still using the the version in your six year old question. You an use any of the technologies supported by Asterisk to communicate between two instances of Asterisk.