H3C Technologies H3C SecPath F1000-E - Manual (Page 136)

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• 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 the packet as requiring
protection and continues to process it. If a deny statement is matched or no match is found, IPsec
considers the packet as not requiring protection and delivers it to the next function module.
• In the inbound direction, all IPsec packets matching a permit statement are processed by IPsec, and
all non-IPsec packets that match a permit statement are discarded.
When defining ACL rules for IPsec, follow these guidelines:
• Permit only the traffic that needs 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, while 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
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.
The following configuration example shows how an improper statement causes unexpected packet
dropping. Only the ACL-related configurations are presented.
Router A connects the segment 1.1.2.0/24 and Router B connects the segment 3.3.3.0/24. On Router A,
apply the IPsec policy group test to the outbound interface of Router A. The IPsec policy group contains
two policies, test 1 and test 2. The ACLs referenced by the two policies each contain a rule that matches
traffic from 1.1.2.0/24 to 3.3.3.0/24. The one referenced in policy test 1 is a deny statement and the one
referenced in policy test 2 is a permit statement. Because test 1 is matched prior to test 2, traffic from
1.1.2.0/24 to 3.3.3.0/24 will match the deny statement and sent as normal traffic. When the traffic
arrives at Router B, it will be dropped if it matches a permit statement in the ACL referenced in the applied
IPsec policy.
Configuration on Router A:
acl number 3000
rule 0 permit ip source 1.1.1.0 0.0.0.255 destination 2.2.2.0 0.0.0.255
rule 1 deny ip
acl number 3001
rule 0 permit ip source 1.1.2.0 0.0.0.255 destination 3.3.3.0 0.0.0.255
rule 1 deny ip
#
ipsec policy test 1 isakmp
security acl 3000
ike-peer aa
proposal 1
#
ipsec policy test 2 isakmp
security acl 3001
ike-peer bb