Prepare the Device for Operation
Chapter 3. Configuration
29
Set Layer 2 MAC Address Resolution on the Local Interface
1. At the
config-ifLocal>
prompt, enter this command:
macAddrResolutionMechanism {none | arp | {gateway <
ipAddress
>}}
For parameter descriptions, go to “macAddrResolutionMechanism” on page 77.
2. Return to configuration mode: enter the
exit
command.
Example
In this example, a local interface configuration on SG2, the HA4000 enters local
interface configuration mode, identifies the default gateway, and then exits local
interface configuration mode.
config>
interface local
config-ifLocal>
macAddrResolutionMechanism gateway 192.168.154.175
config-ifLocal>
exit
config>
Configure the PMTU
The path maximum transmission unit (PMTU) is the end-to-end MTU from target
to destination. Valid PMTU values on the HA4000 range from 128 through 12,160
bytes. The default PMTU size is 3072 bytes.
In these cases, adjust the PMTU size:
z
If jumbo frame processing capabilities are needed (2944-12,160 bytes),
z
If the local side devices has DF bit set, the PMTU size must be set to a number
smaller than the smallest MTU in the path
Older Layer 2 devices are more likely to require frames of a certain size than are
newer, Layer 3 devices. Check with your network administrator about the
configuration of the devices connected to the HA4000 on the local interface. If the
device on the WAN side of the HA4000 is dropping packets, it is an indication that
the PMTU size needs to be adjusted.
HA4000-MTU Interactions
z
When you set an MTU size, the HA4000 detects LAN packets that have the DF
bit set (see “Configure DF Bit Handling” on page 30) and exceed the MTU size
(minus encryption overhead).
When this condition is detected, the HA4000 drops the packet and issues an
MTU discovery packet to the source host, informing it to reduce its MTU. The
HA4000 suggests an MTU value of the actual MTU size minus the encryption
overhead.
z
When you specify the total MTU size, the HA4000 subtracts the IPSec header
overhead from the specified PMTU value to calculate the actual PMTU size that
it asks the device to send.
For example, if an HA4000 MTU size of 1500 is specified and the encryption
overhead is 40 bytes, the adjusted MTU, from the HA4000 gateway’s
perspective, is 1460 bytes (1500 minus 40).
