R2511-HP MSR Router Series Security Configuration Guide(V5)

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Subsequent data flows search the session entries according to the quintuplet to find a matched item. If
found, the data flows are processed according to the tunnel information. Otherwise, they are processed
according to the original IPsec process: search the policy group or policy at the interface, and then the
matched tunnel.
The session processing mechanism of IPsec saves intermediate matching procedures, improving the IPsec
forwarding efficiency.
To set the IPsec session idle timeout:
Ste
p
Command Remar
k
1. Enter system view.
system-view N/A
2. Set the IPsec session idle
timeout.
ipsec session idle-time seconds
Optional.
300 seconds by default
Enabling ACL checking of de-encapsulated IPsec packets
In tunnel mode, the IP packet that was encapsulated in an inbound IPsec packet might not be an object
that is specified by an ACL to be protected. For example, a forged packet is not an object to be protected.
If you enable ACL checking of de-encapsulated IPsec packets, all packets failing the checking will be
discarded, improving the network security.
To enable ACL checking of de-encapsulated IPsec packets:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enable ACL checking of
de-encapsulated IPsec
packets.
ipsec decrypt check
Optional.
Enabled by default.
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 and consumes large amounts of
resources and degrades performance, resulting in DoS. IPsec anti-replay checking, when enabled, is
performed before the de-encapsulation process, reducing resource waste.
In some cases, however, the sequence numbers of some normal service data packets might be out of the
current sequence number range, and the IPsec anti-replay function might drop them as well, affecting the
normal communications. If this happens, disable IPsec anti-replay checking or adjust the size of the
anti-replay window as required.
IPsec anti-replay checking does not affect manually created IPsec SAs. According to the IPsec protocol,
only IPsec SAs negotiated by IKE support anti-replay checking.