DNS: Basics of Stub Zone, Delegation & Conditional Forwarding

Stub Zone:

Stub Zone is a copy of zone which contains the following records,

SOA - Start of Authority record

NS - Name Server record - Authoritative DNS servers of the zone

A - IP address mapping for the Authoritative DNS Servers of the zone.

This is good than a normal forwarder if there are changes in DNS server not managed by us. It automatically updates SOA, NS and A records. There will be part time zone transfers.

Delegation:

DNS delegation can be simply explained by the process used by Root servers ('.') to point to its top level domains. When a request for google.com is received by the root server, it provides the nameserver address of 'com' and which inturn gives the nameserver address of 'google'. This is a good example of DNS delegation.

The delegated domain should be a child domain.

When we delegate a child domain to its parent, its SOA and NS records will be created in the parent domain.

The parent domain does not require the permission of its sub-domain for delegation.

Conditional Forwarding:

In forwarding, the DNS server will forward any query that cannot be resolved by that server to a DNS server IP address set as forwarder. We can set any DNS server in the world as a forwarder (Provided it resolves the query). But in conditional forwarding, we can specify a DNS domain name also. Only the queries intended for that domain will be sent to the forwarded DNS.