Workshop

Previous Table of Contents Next
Each SNMP agent can be configured to broadcast a trap to the network (trap is just another word for an
alert). If your network management station is listening for traps, it will raise a red flag to let you know
about it. For example, it can page you or do whatever you wish. Traps provide excellent ways of letting
you know that something is wrong with your network.
However, in real life, a trap can also be a silly extravaganza. For example, the print servers that we use in
my office will all send an SNMP trap out when their printers are offline. Argh! Give me a break. We’ve
got hundreds of printers out there on the network, many of which are purposely offline at any given time
(to change paper, add forms, and so on). There’s no way I want all of them sending traps to my network
management station every time this happens. Fortunately, when I configured the print server, I had the
option to turn off this trap. (See Figure 22.2.)
Figure 22.2 A dedicated print server with an SNMP configuration via a Telnet session.
Some SNMP agents can be configured to send several different “levels” of traps to your network
manager. This way, you don’t get paged for silly stuff. For example, my GroupWise MIB defines certain
traps as “informational” (for instance, when the post office first starts up) and others as “critical” (for
instance, when the post office must go down). Obviously, I’d like to be paged for critical issues but not
for informational ones.
RMON
The Internet MIBs (MIB-I and MIB-II) are a set of variables that allow individual devices to keep track
of their internal status. But what about the status of the segment that the devices are on? That’s where
RMON comes in. RMON (Remote Monitoring) is an MIB defined specifically for a probe device—that
is, a device whose sole purpose is to keep track of network traffic statistics. Is this much like a network
analyzer? Well, yes and no. Each RMON probe does keep track of network statistics much like your
analyzer does when it’s capturing packets. However, RMON probes aren’t expected to sit there and
continually capture packets; instead, they’re meant to sit there and continually gather statistical data
about the network and other network stations. (Yes, some RMON probes will also act to capture specific
packets from the network in conjunction with a network analyzer.)
Because RMON probes are always active, when you have a problem, there’s a pretty good chance that