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Configuring IPsec anti-replay
IPsec anti-replay protects networks against anti-replay attacks by using a sliding window mechanism
called anti-replay window. This feature checks the sequence number of each received IPsec packet
against the current IPsec packet sequence number range of the sliding window. If the sequence
number is not in the current sequence number range, the packet is considered a replayed packet
and is discarded.
IPsec packet de-encapsulation involves complicated calculation. De-encapsulation of replayed
packets is not required, and the de-encapsulation process consumes large amounts of resources
and degrades performance, resulting in DoS. IPsec anti-replay can check and discard replayed
packets before de-encapsulation.
In some situations, service data packets are received in a different order than their original order. The
IPsec anti-replay feature drops them as replayed packets, which impacts communications. If this
happens, disable IPsec anti-replay checking or adjust the size of the anti-replay window as required.
IPsec anti-replay does not affect manually created IPsec SAs. According to the IPsec protocol, only
IKE-based IPsec SAs support anti-replay checking.
IMPORTANT:
•
Failure to detect anti-replay attacks might result in denial of services. If you want to disable IPsec
anti-replay, make sure you understand the impact of the operation on network security.
•
Set the anti-replay window size as small as possible to reduce the impact on system
performance.
•
IPsec anti-replay requires that packets on the same interface be processed on the same slot. To
perform IPsec anti-replay on a multichassis IRF fabric for a global interface, use the
service
command in interface view to specify a service processing slot for that interface. Global
interfaces (such as VLAN or tunnel interfaces) are virtual interfaces that might have physical
ports across the IRF member devices. For more information about the
service
command, see
Layer 2—LAN Switching Command Reference
or
Layer 3—IP Services Command Reference
.
To configure IPsec anti-replay:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enable IPsec anti-replay.
ipsec anti-replay check
By default, IPsec anti-replay is
enabled.
3.
Set the size of the IPsec
anti-replay window.
ipsec anti-replay window
width
The default size is 64.
Configuring IPsec anti-replay redundancy
This feature synchronizes the following information from the active device to the standby device at
configurable packet-based intervals:
•
Lower bound values of the IPsec anti-replay window for inbound packets.
•
IPsec anti-replay sequence numbers for outbound packets.
This feature, used together with IPsec redundancy, ensures uninterrupted IPsec traffic forwarding
and anti-replay protection when the active device fails.
To configure IPsec anti-replay redundancy:
Summary of Contents for FlexFabric 5940 SERIES
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