Configuring The Ipsec Anti-Replay Function; Binding A Source Interface To An Ipsec Policy - HP VSR1000 Security Configuration Manual

To enable ACL checking for de-encapsulated packets:
Step
1. Enter system view.
2. Enable ACL checking for
de-encapsulated packets.

Configuring the IPsec anti-replay function

The IPsec anti-replay function protects networks against anti-replay attacks by using a sliding window
mechanism called anti-replay window. This function 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 function 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:
IPsec anti-replay is enabled by default. Failure to detect anti-replay attacks might result in denial of
•
services. Use caution when you disable IPsec anti-replay.
• Specify an anti-replay window size that is as small as possible to reduce the impact on system
performance.
To configure IPsec anti-replay:
Step
1. Enter system view.
2. Enable IPsec anti-replay.
3. Set the size of the IPsec
anti-replay window.

Binding a source interface to an IPsec policy

For high availability, a core device is usually connected to an ISP through two links, which operate in
backup or load sharing mode. The two interfaces negotiate with their peers to establish IPsec SAs
respectively. When one interface fails and a link failover occurs, the other interface needs to take some
time to re-negotiate SAs, resulting in service interruption.
Command
system-view
ipsec decrypt-check enable
Command
system-view
ipsec anti-replay check
ipsec anti-replay window width
188
Remarks
N/A
By default, this feature is enabled.
Remarks
N/A
By default, IPsec anti-replay is
enabled.
The default size is 64.