D-Link DGS-3224TGR - Switch User Manual - Snmp
DGS-3224TGR Gigabit Ethernet Switch User’s Guide
modify MIBs, you can also get the MIB values and change them (if the MIBs’ attributes permit the write
operation). This process however can be quite involved, since you must know the MIB OIDs and retrieve
them one by one.
SNMP
The Simple Network Management Protocol (SNMP) is an OSI layer 7 (the application layer) protocol for
remotely monitoring and configuring network devices. SNMP enables network management stations to
read and modify the settings of gateways, routers, switches, and other network devices. SNMP can be
used to perform many of the same functions as a directly connected console, or can be used within an
integrated network management software package such as HP OpenView or DView.
SNMP performs the following functions:
• Sending and receiving SNMP packets through the IP protocol.
• Collecting information about the status and current configuration of network devices.
• Modifying the configuration of network devices.
The DGS-3224TGR has a software program called an ‘agent’ that processes SNMP requests, but the
user program that makes the requests and collects the responses runs on a management station (a
designated computer on the network). The SNMP agent and the user program both use the UDP/IP
protocol to exchange packets.
Authentication
The authentication protocol ensures that both the router SNMP agent and the remote user SNMP
application program discard packets from unauthorized users. Authentication is accomplished using
‘community strings’, which function like passwords. The remote user SNMP application and the router
SNMP must use the same community string.
Packet Forwarding
The switch enters the relationship between destination MAC or IP addresses and the Ethernet port or
gateway router the destination resides on into its forwarding table. This information is then used to
forward packets. This reduces the traffic congestion on the network, because packets, instead of being
transmitted to all ports, are transmitted to the destination port only. Example: if Port 1 receives a
packet destined for a station on Port 2, the switch transmits that packet through Port 2 only, and
transmits nothing through the other ports. This process is referred to as ‘learning’ the network
topology.
MAC Address Aging Time
The Aging Time affects the learning process of the Switch. Dynamic forwarding table entries, which are
made up of the source and destination MAC addresses and their associated port numbers, are deleted
from the table if they are not accessed within the aging time.
The aging time can be from 10 to 1,000,000 seconds with a default value of 300 seconds. A very long
aging time can result in dynamic forwarding table entries that are out-of-date or no longer exist. This
may cause incorrect packet forwarding decisions by the Switch.
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