User manual

Advanced DNS

Cobalt Qube 3 User Manual 231

Retry interval

Due to a connection or service failure, a secondary DNS server may be unable to

refresh data from the primary server. The secondary DNS server attempts to

refresh data after the interval speciﬁed for trying again.

Expire interval

A secondary DNS server may be unable to refresh data from the primary server

for a prolonged period of time. After the interval speciﬁed for expiry, the

secondary server stops serving name requests.

Time-to-live period (TTL)

A caching DNS server other than the primary and secondary DNS servers for this

domain or network can cache record lookups for the TTL period. During the TTL

period, a caching DNS server does not poll the primary or secondary DNS

servers for repeated lookups of the same record.

Conﬁguring the server settings

You can also conﬁgure the server settings and the zone transfer access control for

the Qube 3 DNS server.

Forwarding server

If the Qube 3 is being used on a private network or in conjunction with a

restrictive ﬁrewall, you can specify a forwarding DNS server(s) by IP address.

Zone transfer

A zone transfer allows another DNS server to download the complete list of hosts

maintained by your DNS server. Zone transfers are used by secondary domain

name servers to synchronize their records with primary domain name servers.

By default, zone transfers are unrestricted. However, you can restrict zone

transfers if you want. By entering a domain name in the Zone Transfer Access

window, you automatically restrict zone transfers. Only the domain names listed

in this window are now able to perform zone transfers.

Zone ﬁle format

You can select a zone ﬁle format for delegating subnets on non-octet boundaries

which is compatible with your local reverse-delegation method. RFC2317 is the

international standard format. Consult your ISP to determine the type of subnet

DNS delegation they are using.