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Cisco 1900 IOS Configuration Commands

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Notice the message received from the switch when the delete nvram

command is used. Once you say yes, the configuration is gone.

Managing the MAC Address Table

Do you remember how bridges and switches filter a network? They use
MAC (hardware) addresses burned into a host's network interface card
(NIC) to make forwarding decisions. The switches create a MAC table that
includes dynamic, permanent, and static addresses. This filter table is created
by hosts sending a frame and by the switch learning the source MAC address
and from which segment and port it was received.

The switch keeps adding new MAC addresses that are sent on the net-

work into the MAC filter table. As hosts are added or removed, the switch
dynamically updates the table. If a device is removed, or if it is not connected
to the switch for a period of time, the switch will age out the entry.

You can see the switch's filter table by using the show mac-address-

table

command. The following output shows the information received

when using this command.

Todd1900EN#sh mac-address-table

Number of permanent addresses : 0

Number of restricted static addresses : 0

Number of dynamic addresses : 4

Address Dest Interface Type Source Interface List

00A0.246E.0FA8 Ethernet 0/2 Dynamic All

0000.8147.4E11 Ethernet 0/5 Dynamic All

0000.8610.C16F Ethernet 0/1 Dynamic All

00A0.2448.60A5 Ethernet 0/4 Dynamic All

The addresses in the table shown are from the four hosts connected to my

1900 switch. They are all dynamic entries, which means the switch looked at
the source address of a frame as it entered the switch interface, and it placed that
address in the filter table. Notice that I have hosts in interfaces 1, 2, 4, and 5.

The Catalyst 1900 switch can store up to 1024 MAC addresses in the

filter table. If the MAC filter table gets full, the switch will flood all new
addresses until one of the existing entries gets aged out.

You can also clear the MAC filter table by using the clear mac-address-

table

command. You can clear dynamic, permanent, and restricted static

addresses. The next switch output shows the different options available
when using this command.

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