Cisco ASA 5505 Configuration Manual page 254

Completing Interface Configuration (All Models)
Configuring Advanced Interface Parameters
This section describes how to configure MAC addresses for interfaces and how to set the MTU.
Information About MAC Addresses
By default, the physical interface uses the burned-in MAC address, and all subinterfaces of a physical
interface use the same burned-in MAC address. A redundant interface uses the MAC address of the first
physical interface that you add. If you change the order of the member interfaces in the configuration,
then the MAC address changes to match the MAC address of the interface that is now listed first. If you
assign a MAC address to the redundant interface using this command, then it is used regardless of the
member interface MAC addresses.
In multiple context mode, if you share an interface between contexts, you can assign a unique MAC
address to the interface in each context. This feature lets the adaptive security appliance easily classify
packets into the appropriate context. Using a shared interface without unique MAC addresses is possible,
but has some limitations. See the
for more information. You can assign each MAC address manually, or you can automatically generate
MAC addresses for shared interfaces in contexts. See the
Context Interfaces" section on page 6-19
generate MAC addresses, you can use this procedure to override the generated address.
For single context mode, or for interfaces that are not shared in multiple context mode, you might want
to assign unique MAC addresses to subinterfaces. For example, your service provider might perform
access control based on the MAC address.
Detailed Steps
Choose the Configuration > Device Setup > Interfaces pane.
Step 1
For the ASA 5505, the Interfaces tab shows by default.
Choose the interface row, and click Edit.
Step 2
The Edit Interface dialog box appears with the General tab selected.
Step 3 Click the Advanced tab.
Step 4 To set the MTU or to enable jumbo frame support (ASA 5580 only), enter the value in the MTU field,
between 300 and 65,535 bytes.
The default is 1500 bytes.
•
•
Enabling or disabling jumbo frame support requires you to reboot the security appliance.
Note
A jumbo frame is an Ethernet packet larger than the standard maximum of 1518 bytes (including Layer
2 header and FCS), up to 9216 bytes. Jumbo frames require extra memory to process, and assigning more
memory for jumbo frames might limit the maximum use of other features, such as access lists.
Cisco ASA 5500 Series Configuration Guide using ASDM
8-26
For the ASA 5580 in single mode—If you enter a value for any interface that is greater than 1500,
then you enable jumbo frame support automatically for all interfaces. If you set the MTU for all
interfaces back to a value under 1500, then jumbo frame support is disabled.
For the ASA 5580 in multiple mode—If you enter a value for any interface that is greater than 1500,
then be sure to enable jumbo frame support in the system configuration. See the
Frame Support (ASA 5580, Multiple Mode)" section on page
"How the Security Appliance Classifies Packets" section on page 6-3
"Automatically Assigning MAC Addresses to
to automatically generate MAC addresses. If you automatically
Chapter 8 Configuring Interfaces
"Enabling Jumbo
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