Reverse Host Name Lookup property

The domain name system (DNS) reverse host name lookup is used to determine what host and domain name a given IP address indicates.

Some administrators cannot or do not want to configure the DNS server for reverse host name lookup. For these environments, NetBackup offers the Reverse Host Name Lookup property to allow, restrict, or prohibit reverse host name lookup.

Administrators can configure the Reverse Host Name Lookup property for each host.

Table: Reverse Host Name Lookup property settings

Property	Description
Allowed setting	The Allowed property indicates that the host requires reverse host name lookup to work to determine that the connection comes from a recognizable server. By default, the host resolves the IP address of the connecting server to a host name by performing a reverse lookup. If the conversion of the IP address to host name fails, the connection fails. Otherwise, it compares the host name to the list of known server host names. If the comparison fails, the host rejects the server and the connection fails.
Restricted setting	The Restricted property indicates that the NetBackup host first attempts to perform reverse host name lookup. If the NetBackup host successfully resolves the IP address of the connecting server to a host name (reverse lookup is successful), it compares the host name to the list of known server host names. If the resolution of the IP address to a host name fails (reverse lookup fails), based on the Restricted setting, the host converts the host names of the known server list to IP addresses (using a forward lookup). The host compares the IP address of the connecting server to the list of known server IP addresses. If the comparison fails, the host rejects the connection from server and the connection fails.
Prohibited setting	The Prohibited property indicates that the NetBackup host does not try reverse host name lookup at all. The host resolves the host names of the known server list to IP addresses using forward lookups. The NetBackup host then compares the IP address of the connecting server to the list of known server IP addresses. If the comparison fails, the NetBackup host rejects the connection from the server and the connection fails.

Property

Description

Allowed setting

The Allowed property indicates that the host requires reverse host name lookup to work to determine that the connection comes from a recognizable server.

By default, the host resolves the IP address of the connecting server to a host name by performing a reverse lookup.

If the conversion of the IP address to host name fails, the connection fails.

Otherwise, it compares the host name to the list of known server host names. If the comparison fails, the host rejects the server and the connection fails.

Restricted setting

The Restricted property indicates that the NetBackup host first attempts to perform reverse host name lookup. If the NetBackup host successfully resolves the IP address of the connecting server to a host name (reverse lookup is successful), it compares the host name to the list of known server host names.

If the resolution of the IP address to a host name fails (reverse lookup fails), based on the Restricted setting, the host converts the host names of the known server list to IP addresses (using a forward lookup). The host compares the IP address of the connecting server to the list of known server IP addresses.

If the comparison fails, the host rejects the connection from server and the connection fails.

Prohibited setting

The Prohibited property indicates that the NetBackup host does not try reverse host name lookup at all. The host resolves the host names of the known server list to IP addresses using forward lookups.

The NetBackup host then compares the IP address of the connecting server to the list of known server IP addresses.

If the comparison fails, the NetBackup host rejects the connection from the server and the connection fails.

Reverse Host Name Lookup property

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