HP 5500 HI Series Configuration Manual page 285

IP address and the source IP address specified in the rule to match the source IP address and the
destination IP address of the traffic.
In the outbound direction, if a permit statement is matched, IPsec considers that the packet requires
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protection and continues to process it. If a deny statement is matched or no match is found, IPsec
considers that the packet does not require protection and delivers it to the next function module.
In the inbound direction:
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Non-IPsec packets that match a permit statement are dropped.
IPsec packets that match a permit statement and are destined for the device itself are
de-encapsulated and matched against the rule again. Only those that match a permit
statement are processed by IPsec.
When you configure an ACL for IPsec, follow these guidelines:
• Permit only data flows that need to be protected and use the any keyword with caution. With the
any keyword specified in a permit statement, all outbound traffic matching the permit statement will
be protected by IPsec and all inbound IPsec packets matching the permit statement will be received
and processed, but all inbound non-IPsec packets will be dropped. This will cause the inbound
traffic that does not need IPsec protection to be all dropped.
Avoid statement conflicts in the scope of IPsec policy groups. When creating a deny statement, be
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careful with its matching scope and matching order relative to permit statements. The policies in an
IPsec policy group have different match priorities. ACL rule conflicts between them are prone to
cause mistreatment of packets. For example, when configuring a permit statement for an IPsec
policy to protect an outbound traffic flow, you must avoid the situation that the traffic flow matches
a deny statement in a higher priority IPsec policy. Otherwise, the packets will be sent out as normal
packets; if they match a permit statement at the receiving end, they will be dropped by IPsec.
An ACL can be specified for only one IPsec policy. ACLs referenced by IPsec policies cannot be used
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by other services.
You must create a mirror image ACL rule at the remote end for each ACL rule created at the local
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end. Otherwise, IPsec may protect traffic in only one direction.
Mirror image ACLs
To make sure that SAs can be set up and the traffic protected by IPsec can be processed correctly at the
remote peer, on the remote peer, create a mirror image ACL rule for each ACL rule created at the local
peer.
If the ACL rules on peers do not form mirror images of each other, SAs can be set up only when both of
the following requirements are met:
• The range specified by an ACL rule on one peer is covered by its counterpart ACL rule on the other
peer.
The peer with the narrower rule initiates SA negotiation. If a wider ACL rule is used by the SA
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initiator, the negotiation request may be rejected because the matching traffic is beyond the scope
of the responder.
Protection modes
The switch supports IPsec for data flows in standard mode. In standard mode, one tunnel protects one
data flow. The data flow permitted by an ACL rule is protected by one tunnel that is established solely for
it.
For more information about ACL configuration, see ACL and QoS Configuration Guide.
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