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SonicOS 5.7: Advanced Switching Feature Guide and Screencast Tutorial
Technical FAQ
How do I view the CAM table on the SonicWALL NSA 2400MX?
The SonicOS 5.7.0.0 user interface or CLI does not provide a way to display the CAM, or MAC Address,
table directly, but provides the same information in the ARP table and on the Switching > L2 Discovery
page.
A Content Addressable Memory (CAM) table is a dynamic, internal, purely Layer 2 mapping between switch
ports and the MAC addresses that are bound to them. The CAM table information is also referred to as the
MAC address table, switching cache, or forwarding data. The CAM table is used to quickly dereference MAC
addresses to the switch ports where they are connected, allowing the speedy switching of traffic out the port
to the destination. The CAM table is populated when the switch receives a data frame on one of its ports
and updates the table with the frame's source MAC address and the port on which it was received.
In SonicOS 5.7.0.0, the information displayed on the the Switching > L2 Discovery page is derived from
three sources:
• MAC address table, internal to the switch (SonicWALL NSA 2400MX)
• ARP table maintained by the gateway
• Layer 2 Discovery Protocol exchanges
To illustrate the difference between the MAC address table and the ARP table, consider a situation where
you have two computers that use static IP addresses and communicate with each other within the same
VLAN. The traffic between them never reaches the IP layer (the traffic is never forwarded, always
switched).
These machines will only show up in the MAC address table of the switch. The Switching > L2 Discovery
page will display the MAC addresses and VLAN for these computers, but nothing else (assuming there is no
discovery protocol agent running on these machines).
If the machines stop communicating for awhile, the switch ages out the MAC address table and the entries
will be gone. If you refresh the Switching > L2 Discovery page, you will no longer see these entries.
On the other hand, if the machines connect to the Internet or to another VLAN, the traffic will be
forwarded and the gateway ARP table is populated with entries for these computers. It is possible for entries
to exist only in the gateway ARP table, but not in the switch MAC address table.
The Switching > L2 Discovery page consolidates entries from the MAC address table and the ARP table,
and displays one entry per machine.
Many switches, such as the HP ProCurve, Dell PowerConnect, or Cisco switches, provide a command to
display the CAM or MAC Address table. For example, the following output is from a Cisco switch running
IOS:
Cisco_L3# show mac-address-table dynamic
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
1 0017.c52e.59ba DYNAMIC Fa0/3
1 0017.c52e.5aa4 DYNAMIC Fa0/4
1 0017.c53c.d425 DYNAMIC Po1
Total Mac Addresses for this criterion: 3
Cisco_L3#
The display shows two dynamic entries for SonicPoint-Ns, connected to switch ports 3 and 4 of the Cisco
switch, and one entry for the LACP Link Aggregation Group, which is connected to a SonicWALL NSA
2400MX and is not blocked by RSTP.