Cisco ASA Series Cli Configuration Manual page 1571

Chapter 1 Configuring IPsec and ISAKMP
access-list access-list-name {deny | permit} ip source source-netmask destination
destination-netmask
Each ACL consists of one or more ACEs that have the same access list name. You create an ACL when
you create its first ACE. The following command syntax creates or adds to an ACL:
access-list access-list-name {deny | permit} ip source source-netmask destination
destination-netmask
In the following example, the ASA applies the IPsec protections assigned to the crypto map to all traffic
flowing from the 10.0.0.0 subnet to the 10.1.1.0 subnet:
access-list 101 permit ip 10.0.0.0 255.255.255.0 10.1.1.0 255.255.255.0
The crypto map that matches the packet determines the security settings used in the SA negotiations.
If the local ASA initiates the negotiation, it uses the policy specified in the static crypto map to create
the offer to send to the specified peer. If the peer initiates the negotiation, the ASA attempts to match the
policy to a static crypto map, and if that fails, then it attempts to match any dynamic crypto maps in the
crypto map set, to decide whether to accept or reject the peer offer.
For two peers to succeed in establishing an SA, they must have at least one compatible crypto map. To
be compatible, a crypto map must meet the following criteria:
•
The crypto map must contain compatible crypto ACLs (for example, mirror image ACLs). If the
responding peer uses dynamic crypto maps, so the ASA also must contain compatible crypto ACLs
as a requirement to apply IPsec.
•
Each crypto map identifies the other peer (unless the responding peer uses dynamic crypto maps).
•
The crypto maps have at least one transform set or proposal in common.
You can apply only one crypto map set to a single interface. Create more than one crypto map for a
particular interface on the ASA if any of the following conditions exist:
•
You want specific peers to handle different data flows.
•
You want different IPsec security to apply to different types of traffic.
For example, create a crypto map and assign an ACL to identify traffic between two subnets and assign
one IKEv1 transform set or IKEv2 proposal. Create another crypto map with a different ACL to identify
traffic between another two subnets and apply a transform set or proposal with different VPN
parameters.
If you create more than one crypto map for an interface, specify a sequence number (seq-num) for each
map entry to determine its priority within the crypto map set.
Each ACE contains a permit or deny statement.
deny ACEs in ACLs applied to crypto maps.
Table 1-3 explains the special meanings of permit and
Cisco ASA Series CLI Configuration Guide
Configuring IPsec
1-21