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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 7 Administering the Switch
Managing the MAC Address Table

Managing the MAC Ad dress Tabl e

The MAC address table contains address information that the switch uses to forward traffic between
ports. All MAC addresses in the address table are associated with one or more ports. The address table
includes these types of addresses:
•Dynamic address: a source MAC address that the switch learns and then ages when it is not in use.
•Static address: a manually entered unicast or multicast address that does not age and that is not lost
when the switch resets.
The ad dress table lists th e des tinat ion MAC addr ess , the ass ocia ted VLAN ID , and por t numbe r
ass ociat ed wi th th e addre ss.
Note For complete syntax and usage infor mation for the comma nds used in this section, r efer to the command
refere nce fo r thi s r ele ase.
This se ctio n c onta ins thi s configu ratio n inf or mat ion:
•Building the A d dress Table, pa ge 7 -54
•MAC Addresses and VLANs, page 7-55
•Default MAC Address Table Configurat ion, page 7-55
•Changin g the Address A ging Time, page 7-55
•Removing Dy na mic Addr ess E ntri es, pa ge 7- 56
•Configuring M AC A ddre ss Not ificatio n Traps, pa ge 7- 56
•Adding and Re moving Static Addr ess Entries, pag e 7-58
•Adding and Re moving Secure Ad dresses, page 7-59
•Displayin g Ad dress Table Ent ries, page 7 -60

Building the Address Table

With mu ltip le MAC addresse s su ppo rted o n al l po rts, yo u ca n con nect any p ort on th e swi tch to
individual workst ations, re peate rs, switch es, routers, or other network devices. T he switch pr ovides
dynami c addressi ng by learning th e source addr ess of packets it rece ives on each por t and ad ding the
address and its associated port number to the address table. As stations are added or removed from the
network, th e switch upd ates th e addre ss table, ad ding new dynamic addr esses an d agin g out those tha t
are no t in use .
The aging interval is configured on a per-switch basis. However, the switch maintains an address table
for each VLAN, and STP can accelerate the aging interval on a per-VLAN basis.
The switch sends packets between any combination of ports, based on the destination address of the
received packet. Using the MAC address table, the switch forwards the packet only to the port or ports
associated with the destination address. If the destination address is on the port that sent the packet, the
packet is filtered a nd not forwar ded. The sw itch always uses the store- and-f orward meth od: com plete
packets a re stor ed and c hecked fo r error s b ef ore tr an smission .