Ipsec Df-Bit - HP FlexNetwork MSR Series Command Reference Manual

Usage guidelines
In tunnel mode, the IP packet encapsulated in an inbound IPsec packet might not be under the
protection of the ACL specified in the IPsec policy. After being de-encapsulated, such packets bring
threats to the network security. In this scenario, you can enable ACL checking for de-encapsulated
IPsec packets. All packets failing the checking are discarded, improving the network security.
Examples
# Enable ACL checking for de-encapsulated IPsec packets.
<Sysname> system-view
[Sysname] ipsec decrypt-check enable

ipsec df-bit

Use ipsec df-bit to configure the DF bit for the outer IP header of IPsec packets on an interface.
Use undo ipsec df-bit to restore the default.
Syntax
ipsec df-bit { clear | copy | set }
undo ipsec df-bit
Default
The DF bit is not configured for the outer IP header of IPsec packets on an interface. The global DF
bit setting is used.
Views
Interface view
Predefined user roles
network-admin
Parameters
clear: Clears the DF bit in the outer IP header. IPsec packets can be fragmented.
copy: Copies the DF bit setting of the original IP header to the outer IP header.
set: Sets the DF bit in the outer IP header. IPsec packets cannot be fragmented.
Usage guidelines
This command is effective only when the IPsec encapsulation mode is tunnel mode. It is not effective
in transport mode because the outer IP header is not added in transport mode.
This command does not change the DF bit for the original IP header of IPsec packets.
If multiple interfaces use an IPsec policy that is bound to a source interface, you must use the same
DF bit setting on these interfaces.
Packet fragmentation and reassembly might cause packet forwarding to be delayed. You can set the
DF bit to avoid the forwarding delay. However, to prevent the IPsec packets from being discarded,
you must make sure the path MTU is larger than the IPsec packet size. As a best practice, clear the
DF bit if you cannot make sure the path MTU is larger than the IPsec packet size.
Examples
# Set the DF bit in the outer IP header of IPsec packets on GigabitEthernet1/0/2.
<Sysname> system-view
[Sysname] interface gigabitethernet 1/0/2
[Sysname-GigabitEthernet1/0/2] ipsec df-bit set
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