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Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring IPsec and ISAKMP
Configuring IPsec
Figure 1-1 Effect of Permit and Deny ACEs on Traffic (Conceptual Addresses)
The simple address notation shown in this figure and used in the following explanation is an abstraction.
An example with real IP addresses follows the explanation.
The objective in configuring Security Appliances A, B, and C in this example LAN-to-LAN network is
to permit tunneling of all traffic originating from one of the hosts shown in Figure 1-1 and destined for
one of the other hosts. However, because traffic from Host A.3 contains sensitive data from the Human
Resources department, it requires strong encryption and more frequent rekeying than the other traffic.
So you will want to assign a special transform set for traffic from Host A.3.
To configure Security Appliance A for outbound traffic, you create two crypto maps, one for traffic from
Host A.3 and the other for traffic from the other hosts in Network A, as shown in the following example:
Crypto Map Seq_No_1
deny packets from A.3 to B
deny packets from A.3 to C
permit packets from A to B
permit packets from A to C
Crypto Map Seq_No_2
permit packets from A.3 to B
permit packets from A.3 to C
After creating the ACLs, you assign a transform set to each crypto map to apply the required IPsec to
each matching packet.
Cascading ACLs involves the insertion of deny ACEs to bypass evaluation against an ACL and resume
evaluation against a subsequent ACL in the crypto map set. Because you can associate each crypto map
with different IPsec settings, you can use deny ACEs to exclude special traffic from further evaluation
in the corresponding crypto map, and match the special traffic to permit statements in another crypto
map to provide or require different security. The sequence number assigned to the crypto ACL
determines its position in the evaluation sequence within the crypto map set.
A.1
A.2
A.3
Human Resources
A
143514
B.1
B.2
B.3
B
C.1
C.2
C.3
C
Internet
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