A CommuniGate Pro Cluster can serve several Shared Domains. If you plan to provide POP and IMAP access to Accounts in those Domains, you may want to assign dedicated IP addresses to those Domains to simplify client mailer setups. See the Access section for more details.
If you use Frontend Servers, only Frontend Servers should have dedicated IP Addresses for Shared Domains. Inter-server communications always use full account names (accountname@domainname), so there is no need to dedicate IP Addresses to Shared Domains on Backend Servers.
If you use the DNS round-robin mechanisms to distribute the site load, you need to assign N IP addresses to each Shared Domain that needs dedicated IP addresses, where N is the number of your Frontend Servers. Configure the DNS Server to return these addresses in the round-robin manner:
In this example, the Cluster is serving two Shared Domains: domain1.dom and domain2.dom, and the Cluster has three Frontend Servers. Three IP addresses are assigned to each domain name in the DNS server tables, and the DNS server returns all three addresses when a client is requesting A-records for one of these domain names. Each time the DNS server "rotates" the order of the IP addresses in its responses, implementing the DNS "round-robin" load balancing (client applications usually use the first address in the DNS server response, and use other addresses only if an attempt to establish a TCP/IP connection with the first address fails).
When configuring these Shared Domains in your CommuniGate Pro Servers, you assign all three IP addresses to each Domain.
If you use a Load Balancer to distribute the site load, you need to place only one "external" IP address into DNS records describing each Shared Domain. You assign one "virtual" (LAN) IP address to each Shared Domain on each Frontend Server:
In this example, the Cluster is serving two Shared Domains: domain1.dom and domain2.dom, and the Cluster has three Frontend Servers. One IP Addresses assigned to each Shared Domain in the DNS server tables, and those addresses are external (Internet) addresses of your Load Balancer. You should instruct the Load Balancer to distribute connections received on each of its external IP addresses to three internal IP addresses - the addresses assigned to your Frontend Servers.
When configuring these Shared Domains in your CommuniGate Pro Servers, you assign these three internal IP addresses to each Domain.
DNS MX-records for Shared Domains can point to their A-records.