Managing The Mac Address Tables; Mac Addresses And Vlans - Cisco Catalyst 2950 Software Manual

Chapter 6 Configuring the System
The Address Resolution Protocol (ARP) associates a host IP address with the corresponding media or
MAC addresses and the VLAN ID. Taking an IP address as input, ARP determines the associated MAC
address. Once a MAC address is determined, the IP-MAC address association is stored in an ARP cache
for rapid retrieval. Then the IP datagram is encapsulated in a link-layer frame and sent over the network.
Encapsulation of IP datagrams and ARP requests and replies on IEEE 802 networks other than Ethernet
is specified by the Subnetwork Access Protocol (SNAP). By default, standard Ethernet-style ARP
encapsulation (represented by the arpa keyword) is enabled on the IP interface.
ARP entries added manually to the table do not age and must be manually removed.
For CLI procedures, refer to the Cisco IOS Release 12.1 documentation on Cisco.com for additional
information and CLI procedures.

Managing the MAC Address Tables

You can manage the MAC address tables that the switch uses to forward traffic between ports. All MAC
addresses in the address tables are associated with one or more ports. These MAC tables include these
types of addresses:
•
•
•
The address tables list the destination MAC address and the VLAN ID, module, and port number
associated with the address. This example shows the list of addresses as they would appear in the
dynamic, secure, or static address table.
------------------------------------------
Vlan
----
1
1
1
10
10
Total Mac Addresses for this criterion:5
For information about the Mac address Notification feature, see the
on page

MAC Addresses and VLANs

All addresses are associated with a VLAN. An address can exist in more than one VLAN and have
different destinations in each. Multicast addresses, for example, could be forwarded to port 1 in VLAN
1 and ports 9, 10, and 11 in VLAN 5.
Each VLAN maintains its own logical address table. A known address in one VLAN is unknown in
another until it is learned or statically associated with a port in the other VLAN. An address can be secure
in one VLAN and dynamic in another. An address can be static in one VLAN and dynamic in another.
78-11380-03
Dynamic address: a source MAC address that the switch learns and then drops when it is not in use.
Secure address: a manually entered unicast address or dynamically learnt address that is usually
associated with a secured port. Secure addresses do not age.
Static address: a manually entered unicast or multicast address that does not age and that is not lost
when the switch resets.
Mac Address Table
Mac Address Type
----------- ----
0001.42e2.cdcd DYNAMIC
0001.96e4.fed6 DYNAMIC
0030.19c6.54dd DYNAMIC
0000.0000.0001 STATIC
0404.0400.0006 DYNAMIC
6-17.
Ports
-----
Fa0/24
Fa0/2
Fa0/24
Fa0/7
Fa0/7
"MAC Address Notification" section
Catalyst 2950 Desktop Switch Software Configuration Guide
Managing the MAC Address Tables
6-15