1. ENUM User Guide
  2. Feature Description
  3. About BIND9

2.4 About BIND9

ENUM uses BIND9 domain name server for interacting with the Domain Name System (DNS).

BIND is a suite of software for interacting with DNS. It acts as an authoritative name server for DNS zones and as well as a recursive resolver in the network.

BIND9 facilitates the following functions:

Access Control

Access Control Lists (ACLs) are the address match lists that give users control over who can access the name server. The ACLs can be configured using the DSR MMI or Graphical User Interface (GUI). You can select any of ther following option for an address:
  • Allowed
  • Blocked

The Blocked ACLs take precedence over allowed ones. For example, if there are two subnets configured with some common IPs as follows:

acl allowed{
172.16.0.0/22;
};
acl blocked{
172.16.1.0/24;
};

In the above example, the subnet 172.16.0.0/22 is allowed, which means that all the IPs in the range 172.16.0.1 - 172.16.3.254 are allowed. And the subnet 172.16.1.0/24 is blocked, which means the IPs in the range 172.16.1.1 - 172.16.1.254 are blocked. As blocked takes precedence, all IPs in the range 172.16.1.1 - 172.16.1.254 are considered as blocked.

Forwarding queries from validated IPs to ENUM application

The configured e164.arp zone allows BIND9 to forward all these queries to vENUM servers.

Load balancing the queries between multiple ENUM MPs

BIND9 load balances the queries between the various vENUM servers. It uses response times from previous queries to select the server that is likely to respond the most quickly. Dynamic adjustment of the recorded response times ensures that all forwarders are queried, even those with slower response times.

Caching

BIND9 caches the responses. The advantages of caching responses are:
  • Improvement in application performance
  • Reduction in the load on the backend
  • Reduction of database cost
  • Elimination of database hotspots