plmn sgsn-mapping   :

Using the plmn sgsn-mapping command, you can
control whether the user under the APN is permitted to obtain the PLMN ID
through the SGSN IP mapping, which is called mapping switch. According to the
table of the mapping between the SGSN IP address segment and the PLMN ID, you
can obtain the PLMN ID of the SGSN, which is also one way to obtain the PLMN
ID.

By default, the mapping switch is on