Source Address Change Detection
Certain switch ports can detect and report changes in the MAC (Ethernet hardware) address of the attached equipment. This is useful when the network administrator intends that only a particular physical device be attached to a particular port. Source Address Change detection is not useful unless the interface is attached to a single end station or IP router port. When the interface is instead attached to a switch or hub port, a Source Address Change will be detected every time a different station on the segment transmits.
When a Source Address Change is detected (i.e. when the Ethernet address of the device attached to the port changes), a
pSError(111) trap will be generated. A variable binding containing the OID of the Source Address Change status MIB variable and its value (which will be “
yes(1)“) is included in the “interesting” variable bindings. From this binding, it is possible to derive the cabinet, slot, and subdevice of the interface that detected the change. Another binding containing the new Source Address is also included when this information is available from the hardware. No
pSErrorClear(112) trap is ever generated due to Source Address Change.
Source Address Change status MIB variables change so quickly that they are generally not useful aside from their inclusion in trap messages. (In some cases, the variable may read “
yes(1)” for only a fraction of a second when a change occurs.) They exist only so that they can be attached as “interesting” variable bindings in a Trap. Traps are the only reliable way to find out about changes in Source Addresses.