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

251
Tasks at a
g
lance
(Optional.) Enabling ACL checking for de-encapsulated packets
(Optional.) Configuring the IPsec anti-replay function
(Optional.) Binding a source interface to an IPsec policy
(Optional.) Enabling QoS pre-classify
(Optional.) Enabling logging of IPsec packets
(Optional.) Configuring the DF bit of IPsec packets
(Optional.) Configuring IPsec RRI
(Optional.) Configuring SNMP notifications for IPsec
Configuring an ACL
IPsec uses ACLs to identify the traffic to be protected.
Keywords in ACL rules
An ACL is a collection of ACL rules. Each ACL rule is a deny or permit statement. A permit statement
identifies a data flow protected by IPsec, and a deny statement identifies a data flow that is not protected
by IPsec. With IPsec, a packet is matched against the referenced ACL rules and processed according to
the first rule that it matches:
• Each ACL rule matches both the outbound traffic and the returned inbound traffic. Suppose there is
a rule rule 0 permit ip source 1.1.1.0 0.0.0.255 destination 2.2.2.0 0.0.0.255. This rule matches
both traffic from 1.1.1.0 to 2.2.2.0 and traffic from 2.2.2.0 to 1.1.1.0.
• In the outbound direction, if a permit statement is matched, IPsec considers that the packet requires
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:
{ 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. By default, the de-encapsulated packets are matched against the rule again.
Only those that match a permit statement are processed. Other packets are dropped. If ACL
checking for de-encapsulated IPsec packets is disabled, the de-encapsulated packets are not
matched against the ACL rule and are directly processed by other modules.
When defining ACL rules 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. 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 all the inbound traffic
that does not need IPsec protection to be dropped.
• Avoid statement conflicts in the scope of IPsec policy entries. When creating a deny statement, be
careful with its matching scope and matching order relative to permit statements. The policy entries
in an IPsec policy 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 entry 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 entry. Otherwise, the packets will be sent