Simple Gateway Monitoring Protocol (SGMP) defined in RFC 1028, allows commands to be issued to application protocol entities to set or retrieve values (integer or octet string types) for use in monitoring the gateways on which the application protocol entities reside. Messages are exchanged using UDP

User Datagram Protocol

The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...

 and utilize unreliable transport methods. Authentication takes place on UDP port 153. Some examples of things that can be monitored are listed below.

1. Network Type for interfaces: IEEE 802.3
   IEEE 802.3
   IEEE 802.3 is a working group and a collection of IEEE standards produced by the working group defining the physical layer and data link layer's media access control of wired Ethernet. This is generally a local area network technology with some wide area network applications...
   
    MAC, IEEE 802.4 MAC, IEEE 802.5 MAC, Ethernet
   Ethernet
   Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
   
   , ProNET-80, ProNET-10, FDDI
   Fiber distributed data interface
   Fiber Distributed Data Interface provides a 100 Mbit/s optical standard for data transmission in a local area network that can extend in range up to . Although FDDI logical topology is a ring-based token network, it does not use the IEEE 802.5 token ring protocol as its basis; instead, its...
   
   , X.25
   X.25
   X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
   
   , Point-to-Point Serial, RPA 1822 HDH, ARPA 1822, AppleTalk
   AppleTalk
   AppleTalk is a proprietary suite of protocols developed by Apple Inc. for networking computers. It was included in the original Macintosh released in 1984, but is now unsupported as of the release of Mac OS X v10.6 in 2009 in favor of TCP/IP networking...
   
   , StarLAN
2. Interface Status (down, up, attempting, etc.)
3. Route Type (local, remote, sub-network, etc.)
4. Routing Protocol (RIP
   Routing Information Protocol
   The Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15....
   
   , EGP
   Exterior Gateway Protocol
   The Exterior Gateway Protocol is a now obsolete routing protocol for the Internet originally specified in 1982 by Eric C. Rosen of Bolt, Beranek and Newman, and David L. Mills. It was first described in RFC 827 and formally specified in RFC 904...
   
   , GGP, IGRP
   Interior Gateway Routing Protocol
   Interior Gateway Routing Protocol is a distance vector interior routing protocol invented by Cisco. It is used by routers to exchange routing data within an autonomous system....
   
   , Hello)

The protocol was replaced by SNMP (Simple Network Management Protocol

Simple Network Management Protocol

Simple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...

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