NoProxy

This directive is only useful for Apache proxy servers within intranets. The NoProxy directive specifies a list of subnets, IP addresses, hosts and/or domains, separated by spaces. A request to a host which matches one or more of these is always served directly, without forwarding to the configured ProxyRemote proxy server(s).

Example:

  ProxyRemote  *  http://firewall.mycompany.com:81
  NoProxy         .mycompany.com 192.168.112.0/21 

Domain

A Domain is a partially qualified DNS domain name, preceded by a period. It represents a list of hosts which logically belong to the same DNS domain or zone (i.e., the suffixes of the hostnames are all ending in Domain).
Examples: .com .apache.org.
To distinguish Domains from Hostnames (both syntactically and semantically; a DNS domain can have a DNS A record, too!), Domains are always written with a leading period.
Note: Domain name comparisons are done without regard to the case, and Domains are always assumed to be anchored in the root of the DNS tree, therefore two domains .MyDomain.com and .mydomain.com. (note the trailing period) are considered equal. Since a domain comparison does not involve a DNS lookup, it is much more efficient than subnet comparison.

SubNet

A SubNet is a partially qualified internet address in numeric (dotted quad) form, optionally followed by a slash and the netmask, specified as the number of significant bits in the SubNet. It is used to represent a subnet of hosts which can be reached over a common network interface. In the absence of the explicit net mask it is assumed that omitted (or zero valued) trailing digits specify the mask. (In this case, the netmask can only be multiples of 8 bits wide.)
Examples:

192.168 or 192.168.0.0

the subnet 192.168.0.0 with an implied netmask of 16 valid bits (sometimes used in the netmask form 255.255.0.0)

192.168.112.0/21

the subnet 192.168.112.0/21 with a netmask of 21 valid bits (also used in the form 255.255.248.0)

As a degenerate case, a SubNet with 32 valid bits is the equivalent to an IPAddr, while a SubNet with zero valid bits (e.g., 0.0.0.0/0) is the same as the constant _Default_, matching any IP address.

IPAddr

A IPAddr represents a fully qualified internet address in numeric (dotted quad) form. Usually, this address represents a host, but there need not necessarily be a DNS domain name connected with the address.
Example: 192.168.123.7
Note: An IPAddr does not need to be resolved by the DNS system, so it can result in more effective apache performance.

See Also: DNS Issues

Hostname

A Hostname is a fully qualified DNS domain name which can be resolved to one or more IPAddrs via the DNS domain name service. It represents a logical host (in contrast to Domains, see above) and must be resolvable to at least one IPAddr (or often to a list of hosts with different IPAddr's).
Examples: prep.ai.mit.edu www.apache.org.
Note: In many situations, it is more effective to specify an IPAddr in place of a Hostname since a DNS lookup can be avoided. Name resolution in Apache can take a remarkable deal of time when the connection to the name server uses a slow PPP link.
Note: Hostname comparisons are done without regard to the case, and Hostnames are always assumed to be anchored in the root of the DNS tree, therefore two hosts WWW.MyDomain.com and www.mydomain.com. (note the trailing period) are considered equal.

See Also: DNS Issues