4
Unicast packets
data packets with a single destination address. Unicast packets are sent
from a single source to a single destination. This node-to-node transmission method is the
predominant form of transmission on
Local Area Networks (LANs)
and across the Internet.
Multicast packets
data packets sent to a selected group of recipients.
Broadcast packets
data packets sent to everyone on the network.
Central/Remote Port Monitoring
Managed switches can contain embedded software or come with installable software that allows
ports to be monitored centrally and/or remotely.
Central port monitoring, as its name implies, provides a central point of control. With this
monitoring method, client software is installed on a central workstation or PC. With this
software, the health and performance of managed switch ports can be monitored from a central
management console, without having to go to the switch’s physical location.
Remote port monitoring allows ports to be monitored using a Web browser or SNMP-based
solutions:
Web-based monitoring allows switch ports to be monitored over the Internet. Switches
that support web-based monitoring include software for assigning an Internet Protocol (IP)
address to the switch. Once the IP address is assigned, you can access the switch from any
PC or workstation that has an Internet connection and a Web browser.
SNMP-based solutions enable industry-standard SNMP and RMON management
methods to be used from any network-management application or in-band via Telnet.
SNMP and RMON management methods are described later in this paper.
Detecting Packet Errors
In addition to detecting data packets, managed switches can detect and record errors associated
with data packets that a port sends or receives. Some network-management tools alert
administrators to problems like excessive packet errors or bandwidth overload on a segment.
Other tools can perform simple baselining, such as computing packets per second versus
collisions per second on a per-port basis.
While the number and types of packet errors that can be tabulated varies between network-
management applications, typical errors include:
Undersize packets
packets smaller than the minimum size defined for IEEE 802.3
packets.
Oversize packets
packets that exceed the maximum length defined for IEEE 802.3
packets.
Jabbers
packets that a port receives from a faulty device that transmits oversize packets
continuously.
Fragments
incomplete data packets that a port sends or received.
Packets that contain a Cyclic Redundancy Check (CRC) or alignment error, which means
the data was corrupted during transmission.
