The segment number that uniquely identifies the virtual
segment to which this DLSw interface is connected.
Current source routing protocols limit this value to
the range 0 - 4095. (The value 0 is used by some
management applications for special test cases.)
A value of 65535 signifies that no virtual segment
is assigned to this interface. For instance,
in a non-source routing environment, segment number
assignment is not required.