Remote Monitoring Revisited (Essential SNMP)

2.8. Remote Monitoring Revisited

A thorough treatment of RMON is beyond the scope of this book, but it's worth discussing the groups that make up RMONv1. RMON probes are typically stand-alone devices that watch traffic on the network segments to which they are attached. Some vendors implement at least some kind of RMON probe in their routers, hubs, or switches. Chapter 9, "Polling and Thresholds" provides an example of how to configure RMON on a Cisco router.

The RMON MIB defines the following 10 groups:

rmon              OBJECT IDENTIFIER ::= { mib-2 16 }
statistics        OBJECT IDENTIFIER ::= { rmon 1 }
history           OBJECT IDENTIFIER ::= { rmon 2 }
alarm             OBJECT IDENTIFIER ::= { rmon 3 }
hosts             OBJECT IDENTIFIER ::= { rmon 4 }
hostTopN          OBJECT IDENTIFIER ::= { rmon 5 }
matrix            OBJECT IDENTIFIER ::= { rmon 6 }
filter            OBJECT IDENTIFIER ::= { rmon 7 }
capture           OBJECT IDENTIFIER ::= { rmon 8 }
event             OBJECT IDENTIFIER ::= { rmon 9 }

RMONv1 provides packet-level statistics about an entire LAN or WAN. The rmon OID is 1.3.6.1.2.1.16 (iso.org.dod.internet.mgmt.mib-2.rmon). RMONv1 is made up of nine groups:

statistics (1.3.6.1.2.1.16.1): Contains statistics about all the Ethernet interfaces monitored by the probe

history (1.3.6.1.2.1.16.2): Records periodic statistical samples from the statistics group

alarm (1.3.6.1.2.1.16.3): Allows a user to configure a polling interval and a threshold for any object the RMON probe records

hosts (1.3.6.1.2.1.16.4): Records traffic statistics for each host on the network

hostTopN (1.3.6.1.2.1.16.5): Contains host statistics used to generate reports on hosts that top a list ordered by a parameter in the host table

matrix (1.3.6.1.2.1.16.6 ): Stores error and utilization information for sets of two addresses

filter (1.3.6.1.2.1.16.7): Matches packets based on a filter equation; when a packet matches the filter, it may be captured or an event may be generated

capture (1.3.6.1.2.1.16.8): Allows packets to be captured if they match a filter in the filter group

event (1.3.6.1.2.1.16.9): Controls the definition of RMON events

RMONv2 enhances RMONv1 by providing network- and application-level statistical gathering. Since the only example of RMON in this book uses RMONv1, we will stop here and not go into RMONv2. However, we encourage you to read RFC 2021 to get a feel for what enhancements this version of RMON brings to network monitoring.