R0106-HP MSR Router Series Security Configuration Guide(V7)

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Enabling ACL checking for de-encapsulated packets
This feature uses the ACL in the IPsec policy to match the IP packets that are de-encapsulated from
incoming IPsec packets in tunnel mode, and it discards the IP packets that fail to match the ACL to avoid
attacks using forged packets.
To enable ACL checking for de-encapsulated packets:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enable ACL checking for
de-encapsulated packets.
ipsec decrypt-check enable By default, this feature is enabled.
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.
• On MSR4000 routers, multiple service cards might process packets for the same global logical
interface. However, IPsec anti-replay requires that packets sent and received on the same global lo
g
ical
interface be processed by the same service card. To implement IPsec anti-replay, use the service
command in the global logical interface view to specify a service card for forwardin
g
the traffic on the
interface.
To configure IPsec anti-replay:
Ste
p
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.