Hi Morteza,
You were able to connect to that switch from a different network because on Catalyst switches, if no ip routing is configured and no ip default-gateway is defined, these switches will simply send an ARP request for every IP packet's destination they need to reach. If the switch connects to a router that has Proxy ARP active, it will respond to this ARP request using its own MAC address. As a result, you will be able to establish connectivity to such a switch. This connectivity comes at a price, though: The ARP cache on the switch can potentially grow very large, depending on how many IP destinations the switch needs to talk to; the ARP traffic can be unreasonably high; if the Proxy ARP functionality is deactivated on the router that is attached to the switch, the connectivity will no longer work.
You can check using show ip arp on your switch to see that there will most probably be several ARP entries recorded, also entries for IP addresses that are outside the switch's management VLAN. This is an indication that the switch relies on Proxy ARP, otherwise it would never ARP for a destination outside its own management VLAN IP space.
It's actually quite insidious, this little featurette on Catalysts.
Best regards,
Peter
