Applying crypto maps to interfaces, Using interface access lists – Cisco ASA 5505 User Manual
Page 1378
64-26
Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter 64 Configuring IPsec and ISAKMP
Configuring IPsec
The tables that follow combine the IP addresses shown in
to the concepts shown in
. The real ACEs shown in these tables ensure that all IPsec packets under evaluation within
this network receive the proper IPsec settings.
You can apply the same reasoning shown in the example network to use cascading ACLs to assign
different security settings to different hosts or subnets protected by a Cisco ASA.
Note
By default, the ASA does not support IPsec traffic destined for the same interface from which it enters.
Names for this type of traffic include U-turn, hub-and-spoke, and hairpinning. However, you can
configure IPsec to support U-turn traffic by inserting an ACE to permit traffic to and from the network.
For example, to support U-turn traffic on Security Appliance B, add a conceptual “permit B B” ACE to
ACL1. The actual ACE would be as follows:
permit 192.168.12.0 255.255.255.248 192.168.12.0 255.255.255.248
Applying Crypto Maps to Interfaces
You must assign a crypto map set to each interface through which IPsec traffic flows. The ASA supports
IPsec on all interfaces. Assigning the crypto map set to an interface instructs the ASA to evaluate all the
traffic against the crypto map set and to use the specified policy during connection or SA negotiation.
Assigning a crypto map to an interface also initializes run-time data structures, such as the SA database
and the security policy database. Reassigning a modified crypto map to the interface resynchronizes the
run-time data structures with the crypto map configuration. Also, adding new peers through the use of
new sequence numbers and reassigning the crypto map does not tear down existing connections.
Using Interface Access Lists
By default, the ASA lets IPsec packets bypass interface ACLs. If you want to apply interface access lists
to IPsec traffic, use the no form of the sysopt connection permit-vpn command.
Table 64-5
Example Permit and Deny Statements for Security Appliance A
Security
Appliance
Crypto Map
Sequence
No.
ACE Pattern
Real ACEs
A
1
deny A.3 B
deny 192.168.3.3 255.255.255.192 192.168.12.0 255.255.255.248
deny A.3 C
deny 192.168.3.3 255.255.255.192 192.168.201.0 255.255.255.224
permit A B
permit 192.168.3.0 255.255.255.192 192.168.12.0 255.255.255.248
permit A C
permit 192.168.3.0 255.255.255.192 192.168.201.0 255.255.255.224
2
permit A.3 B
permit 192.168.3.3 255.255.255.192 192.168.12.0 255.255.255.248
permit A.3 C
permit 192.168.3.3 255.255.255.192 192.168.201.0 255.255.255.224
B
None needed
permit B A
permit 192.168.12.0 255.255.255.248 192.168.3.0 255.255.255.192
permit B C
permit 192.168.12.0 255.255.255.248 192.168.201.0 255.255.255.224
C
None needed
permit C A
permit 192.168.201.0 255.255.255.224 192.168.3.0 255.255.255.192
permit C B
permit 192.168.201.0 255.255.255.224 192.168.12.0 255.255.255.248