Office Communications Server uses DNS (Domain Name Services) to publish Enterprise pools and Edge Servers so that they can be discoverable by other home servers and Edge Servers. Standard Edition Servers automatically publish their FQDN as A (Host) records in DNS; however, the FQDN of Enterprise pools need to be published in DNS manually by administrators. Administrators create an A record for the Enterprise pool's FQDN, mapped to the virtual IP (VIP) of the Enterprise pool's hardware load balancer (HLB). To federate with other partners and public IM connectivity (PIC) partners or allow remote users to connect to the internal Office Communication Server infrastructure, the external network interface card (NIC) of Edge Servers deployed in the network perimeter must be published in the public DNS.
Office Communications Server introduces the concept of Session Initiation Protocol (SIP) namespaces or domains to route SIP requests internally and externally by using DNS. This is similar to how e-mail messages are routed.
When installing Office Communications Server 2007, the default SIP domain server becomes authoritative for the Active Directory's forest (that is, root domain) name. For example, if your forest's FQDN is contoso.com, Office Communications Server will be authoritative for the SIP domain @contoso.com. In the case of a multitree Active Directory forest, Office Communications Server 2007 picks up only the first tree's FQDN as its SIP domain. The other tree's FQDN must be defined manually. However, this default namespace is probably not the namespace you will want to expose externally. In most cases, you will want to make the user's SIP URI identical to the user's e-mail address for simplicity. This is not a requirement, but it keeps the user's corporate identity consistent. If your corporate e-mail namespace does not match your Active Directory root domain FQDN, you must change the default SIP namespace to match your Simple Mail Transfer Protocol (SMTP) namespace. Fortunately, you can modify the list of SIP domains.
You can easily modify the set of authoritative SIP domains through the Administrative Tools MMC. To open global settings, right-click the Forest node and then select Properties. The General tab appears by default. Use the Add and Remove buttons to modify the list of authoritative SIP domains, as shown in Figure 3-15.
Users in your organization must be enabled for Office Communications Server with a SIP URI that has a domain suffix supported by the Office Communications Servers in your organization.
After the initial configuration, there is little need to add or remove SIP domains; however, sometimes this need does arise. For example, if a company changes its public identity, the old SIP domain must be discontinued and the new SIP domain must be added. If a company with an existing deployment of Office Communications Server is merged with your organization and you want to support only a single SIP domain namespace, the acquired company's SIP domain name must be added to your Domain list until the migration is completed. For these and other reasons, simply adding the new SIP domain to the Domain list and removing the old SIP domain is not sufficient. In addition to this step, you must migrate all users whose SIP URI uses the acquired SIP domain to the existing SIP domain. To remain valid, each user's contacts also need to be updated from the acquired SIP domain to the new corporate SIP domain.
Migrate users from one SIP namespace to another
Performing step 1 is easy; however, steps 2 and 3 become more challenging because there are no tools to perform these steps. Fortunately, Office Communications Server 2007 provides Windows Management Instrumentation (WMI) APIs that can be leveraged via scripting (for example, VBScript, PowerShell) to automate these steps.
One approach is to query all users in Active Directory that are enabled for Office Communications Server, determine if any user matches the source SIP domain to change, and change the domain portion of the SIP URI (leaving the username portion intact) to the target SIP domain desired. Because users could have added a contact with a SIP URI that you must change to match the new SIP domain name, this utility needs to "peek" into each user enabled for Office Communications Server, check whether any contact's SIP URI matches the same source SIP domain, and update the domain portion of the contact's SIP URI. Step 4 involves requesting a new server certificate from your preferred public certificate authority (CA) provider. For additional details, see the Configuring the Subject Alternative Name section later in this chapter.