1. ACLI Configuration Guide
  2. System Configuration
  3. DNS on the OCSBC

DNS on the OCSBC

DNS service is best known for providing resolution of internet domain names to IP addresses. Domain names are easy to remember, but connections require IP addresses. DNS deployments can also provide more comprehensive services, if required. For example, the a DNS client may need the resolution of multiple IP addresses to a single domain name, or the types of service provided by a given server. The Oracle® Enterprise Session Border Controller (E-SBC) uses DNS predominantly for resolving FQDNs to IP addresses so that it can support sessions.

When configured, the E-SBC performs DNS client functions per RFC1034 and RFC1035. The user can define one primary DNS server and two backup DNS servers for the E-SBC to query a domain for NAPTR (service/port), SRV (FQDN), AAAA (IPv6), and A (IP address) information. A common example of the E-SBC using DNS is to locate a SIP server via server location discovery, as described in RFC 3263. An applicable context is identifying a callee so the E-SBC can place a call.

There are multiple reasons for the E-SBC to query a DNS server. In each case, the E-SBC follows this high level procedure:

  1. The system determines the egress realm.
  2. The system identifies the egress network interface.
  3. From the egress network interface, the system refers to the configured DNS server(s).
  4. The system issues the DNS query to the primary server, then any configured backup servers, based on the function and the initial information it has.
  5. The system performs recursive lookups or subsequent queries based on, for example, information provided in NAPTR resource responses, until it has one or more resolutions for the FQDN.
  6. The system continues processing using the resolved FQDN(s) or indicates it cannot reach that FQDN.

Note:

DNS queries may require host routes.

The E-SBC also has a DNS Application Layer Gateway (ALG) function that operates independently of its client function. See the DNS ALG Chapter in this document for information about using this ALG.

Closely related to DNS, ENUM service also provides a method of defining a target endpoint, translating E.164 phone numbers to FQDNs. The E-SBC uses configured ENUM objects for routing calls. ENUM uses Naming Authority Pointers (NAPTR) records defined in RFC 2915 in order to identify available ways or services for contacting a specific node identified through the E.164 number. See the Session Routing and Load Balancing chapter for information on ENUM services and configuration.

The E-SBC can cache NAPTR, SRV and A records to speed up DNS and ENUM query processes. The user configures the applicable enum-config to cache these records, providing ENUM and, when configured, DNS with applicable resolutions without having to re-query a server. These resolutions become available to all internal lookup processes that may be generated within the E-SBC.