With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cnatInterfaceRealm
cnat Interface Realm
1.3.6.1.4.1.9.10.77.1.1.4.1.2
This object identifies whether this interface is connected to the private or the public realm.
Back to CISCO-IETF-NAT-MIB MIB page.
IPHost Network monitor allows you to monitor cnatInterfaceRealm on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco routers right now.
