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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.
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 Switch 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.
Packet Forwarding
The Switch learns the network configuration and uses this information to forward packets. This
reduces the traffic congestion on the network, because packets, instead of being transmitted to all
segments, are transmitted to the destination 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.
A listing of CLI commands for Switch forwarding and related settings can be found in the CLI
Reference Manual in the chapter titled, Layer 2 FDB Commands. Use the menus contained in the
Forwarding and Filtering folder of the web manager to make entries into the Unicast and Multicast
forwarding tables (see page 65).
MAC Address Aging Time
The Aging Time affects the learning process of the Switch. Dynamic forwarding table entries are made
up of the source and destination MAC addresses and their associated port numbers and are deleted
from the table if they are not accessed within the aging time.
The aging time can be adjusted from 10 to 2200 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long aging time can result in dynamic forwarding table entries that are out-of-date or no longer exist.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. To change MAC Address Aging
Time use the CLI command
web manager (page 52).
If the Aging Time is too short however, many entries may be aged out too soon. This will result in a
high percentage of received packets whose source addresses cannot be found in the forwarding table,
in which case the switch will broadcast the packet to all ports, negating many of the benefits of having
a switch.
Static forwarding entries are not affected by the aging time.
Packet Filtering
The switch uses a filtering database to segment the network and control communication between
segments. It can also filter packets off the network for intrusion control. Static filtering entries can be
made by MAC Address.
Each port on the switch is a unique collision domain and the switch filters (discards) packets whose
destination lies on the same port as where it originated. This keeps local packets from disrupting
communications on other parts of the network.
For intrusion control, whenever a switch encounters a packet originating from or destined to a MAC
address or an IP Address entered into the filter table, the switch will discard the packet.
The switch does some filtering automatically:
Dynamic Filtering: automatic learning and aging of MAC addresses and their location on the network.
Filtering occurs to keep local traffic confined to its segment.
Switch Management
DES-7000/DES-7100 Layer 2 Switch User's Guide
config fdb aging_time
or use the Advanced Settings menu of the
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