IEC61850 SuBNetwork Address

Hi, to everybody.

I am trying (and succed) to connect to a few switches supporting IED61850. My question is about IEC61850 SubNetworks. My computer's IP is 172.16.4.132 :

The IED device IP is 172.16.7.253 (in the same subnet cause the mask is 255.255.252.0).

The connection works without any problem. The 'problem' is that i can set up the ip of the subnetwork to 'any' value (i.e. 192.168.1.132) without disturbing the communication.

Why ?

Best Regards