Reference : RFC 2863: The Interfaces Group MIB - ifAliasA textual description of the interface.
A server implementation MAY map this leaf to the ifAlias
MIB object. Such an implementation needs to use some
mechanism to handle the differences in size and characters
allowed between this leaf and ifAlias. The definition of
such a mechanism is outside the scope of this document.
Since ifAlias is defined to be stored in non-volatile
storage, the MIB implementation MUST map ifAlias to the
value of 'description' in the persistently stored
datastore.
Specifically, if the device supports ':startup', when
ifAlias is read the device MUST return the value of
'description' in the 'startup' datastore, and when it is
written, it MUST be written to the 'running' and 'startup'
datastores. Note that it is up to the implementation to
decide whether to modify this single leaf in 'startup' or
perform an implicit copy-config from 'running' to
'startup'.
If the device does not support ':startup', ifAlias MUST
be mapped to the 'description' leaf in the 'running'
datastore.