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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 57
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 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in dynamic forwarding table entries that are out-of-date or no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.
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.
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 or IP Address filtering.
Each port on the switch is a unique collision domain and the
switch filters (discards) packets whose destination lies on the