DNS performs a crucial role in enabling user access
to network resources so that users need not remember IP addresses
and individual computers need not store a huge volume of domain
names mapped to IP addresses. DNS employs a client/server model;
a DNS server resolves a query for a DNS client by looking up the
domain in its cache and if necessary sending queries to other servers
until it can respond to the client with the corresponding IP address.
The DNS structure of domain names is hierarchical: the top-level domain (TLD) in
a domain name can be a generic TLD (gTLD): com, edu, gov, int, mil,
net, or org (gov and mil are for the United States only) or a country
code (ccTLD), such as au (Australia) or us (United States). ccTLDs
are generally reserved for countries and dependent territories;
they are sometimes used in an unrelated context.
A fully qualified domain name (FQDN) includes at a minimum a
host name, a second-level domain, and a TLD to completely specify
the location of the host in the DNS structure. For example, www.paloaltonetworks.com
is an FQDN.
Wherever a Palo Alto Networks firewall uses an FQDN in the user
interface or CLI, the firewall must resolve that FQDN using DNS.
Depending on where the FQDN query originates, the firewall determines
which DNS settings to use to resolve the query. The firewall uses
DNS in a number of ways:
You can Enable DNS Proxy and
then enable evasion signatures for threat prevention.
When you Configure an Interface as a DHCP Server,
the firewall acts as a DHCP Server and sends DNS information to
its DHCP clients so the provisioned DHCP clients can reach their
respective DNS servers.