Cisco ASA 5505 Configuration Manual page 1297

Asa 5500 series

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Configuring IKE, Load Balancing, and NAC

Changing the MTU or the pre-fragmentation option on any interface tears down all existing connections.

For example, if 100 active tunnels terminate on the public interface, and you change the MTU or the

pre-fragmentation option on the external interface, all of the active tunnels on the public interface are

The following table shows the modes in which this feature is available:

Firewall Mode

Edit IPsec Pre-Fragmentation Policy

Use this pane to modify an existing IPsec pre-fragmentation policy and do-not-fragment (DF) bit policy

for an interface selected on the parent pane, Configuration > VPN > IPsec > Pre-Fragmentation

The following table shows the modes in which this feature is available:

Pre-Fragmentation—Shows the current pre-fragmentation configuration for every configured

Interface—Shows the name of each configured interface.

Pre-Fragmentation Enabled—Shows, for each interface, whether pre-fragmentation is

DF Bit Policy—Shows the DF Bit Policy for each interface.

Edit—Displays the Edit IPsec Pre-Fragmentation Policy dialog box.

Security Context

Transparent Single

Interface—Identifies the chosen interface. You cannot change this parameter using this dialog box.

Enable IPsec pre-fragmentation—Enables or disables IPsec pre-fragmentation. The adaptive

security appliance fragments tunneled packets that exceed the MTU setting before encapsulating

them. If the DF bit on these packets is set, the adaptive security appliance clears the DF bit,

fragments the packets, and then encapsulates them. This action creates two independent,

non-fragmented IP packets leaving the public interface and successfully transmits these packets to

the peer site by turning the fragments into complete packets to be reassembled at the peer site.

DF Bit Setting Policy—Choose the do-not-fragment bit policy: Copy, Clear, or Set.

Cisco ASA 5500 Series Configuration Guide using ASDM

Configuring IPsec

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