From OpenNMS

IfAlias refers to an administrator-assigned name for an interface on a network device such as a switch or router. IfAlias is p[art of the if-mib ifXtable. OpenNMS stores this for each SNMP interface in its snmpinterface table. It is used in several places within the OpenNMS WebUI and can be included in events and notifications.

Most network devices have a way to set this string. The ifAlias for an interface may be set via SNMP or through a management interface on the network device. IfAliases might be 1) the names of the server attached to the interface, or 2) the names of the remote sites or their circuit IDs. This can be assigned on Cisco devices with the "description" command on a particular interface. On Extreme Network Extremeware based switches, this is defined as the port "display-string".

From RFC2233:

"This object is an 'alias' name for the interface as specified by a network manager, and provides a non-volatile 'handle' for the interface.

On the first instantiation of an interface, the value of ifAlias associated with that interface is the zero-length string. As and when a value is written into an instance of ifAlias through a network management set operation, then the agent must retain the supplied value in the ifAlias instance associated with the same interface for as long as that interface remains instantiated, including across all re- initializations/reboots of the network management system, including those which result in a change of the interface's ifIndex value.

An example of the value which a network manager might store in this object for a WAN interface is the (Telco's) circuit number/identifier of the interface.

Some agents may support write-access only for interfaces having particular values of ifType. An agent which supports write access to this object is required to keep the value in non-volatile storage, but it may limit the length of new values depending on how much storage is already occupied by the current values for other interfaces."