Managing The Mac Address Table; Overview; Adding Entries To The Mac Address Table; Mac Address Table Entry Types - Foundry Networks NetIron M2404C User Manual

Foundry NetIron M2404C and M2404F Metro Access Switches

Managing the MAC Address Table

Overview

The MAC (Media Access Control) address is the unique hardware number that identifies user's
computer on a local area network (LAN) or other network. On an Ethernet LAN, this address is the
same as the Ethernet address. When the user are connected to the Internet from the computer (or
host as the Internet protocol sees it), a correspondence table associates the IP address to user's
computer physical (MAC) address on the local area network.
The MAC address is used by the Media Access Control sub-layer of the Data-Link Control (DLC)
of the telecommunication protocol. Each physical device type has a different MAC sub-layer. The
other sub-layer level in the DLC layer is the Logical Link Control sub-layer.
The MAC Address table contains forwarding database information. The device uses the forwarding
database to forward packets to the appropriate bridge in the bridge group. All MAC addresses in
the address tables are associated with one or more ports (except for the device own MAC address).
The address tables hold the destination MAC address, the VLAN ID, the MAC address priority and
the port number associated with each address.

Adding Entries to the MAC Address Table

Entries are added into the MAC address table in the following ways:
1. The device can learn entries by examining packets it receives. The system updates its MAC
address table with the source MAC address from a packet, the VLAN, and the port identifier
on which the source packet is received. The ability to learn MAC addresses can be enabled or
disabled on a port-by-port basis. You can also limit the number of addresses that can be
learned on a port, or the user can "shutdown" the current port and prevent additional MAC
address learning.
2. Entries can be entered and updated using the command-line interface (CLI).
3. The device self MAC address entries are added by the system for each created VLAN.
4. Multicast MAC address entries are added by the multicast protocols (such as GMRP, IGMP
snooping, etc.).

MAC Address Table Entry Types

The following entry types can exist in the MAC address table:
• Dynamic entries - To learn a dynamic entry, the device examines packets to determine the
source MAC address, VLAN, and port information. The device then creates or updates a MAC
address table entry for that MAC address. Initially, all entries in the database are dynamic,
except for certain entries created by the device.
Dynamic entries are flushed and relearned (updated) when any of the following occurs:
• A VLAN is deleted.
• A port mode is changed (tagged/untagged).
Managing the MAC Address Table © 2008 Foundry Networks, Inc.
Switch Administration (Rev. 03)
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