![background image](http://html.mh-extra.com/html/cisco/5505-asa-firewall-edition-bundle/5505-asa-firewall-edition-bundle_cli-configuration-manual_186241572.webp)
1-22
Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring IPsec and ISAKMP
Configuring IPsec
ACEs containing deny statements filter out outbound traffic that does not require IPsec protection
(for example, routing protocol traffic). Therefore, insert initial deny statements to filter outbound traffic
that should not be evaluated against permit statements in a crypto access list.
For an inbound, encrypted packet, the security appliance uses the source address and ESP SPI to
determine the decryption parameters. After the security appliance decrypts the packet, it compares the
inner header of the decrypted packet to the permit ACEs in the ACL associated with the packet SA. If the
inner header fails to match the proxy, the security appliance drops the packet. It the inner header matches
the proxy, the security appliance routes the packet.
When comparing the inner header of an inbound packet that was not encrypted, the security appliance
ignores all deny rules because they would prevent the establishment of a Phase 2 SA.
Note
To route inbound, unencrypted traffic as clear text, insert deny ACEs before permit ACEs.
shows an example LAN-to-LAN network of ASAs.
Table 1-3
Special Meanings of Permit and Deny in Crypto Access Lists Applied to Outbound Traffic
Result of Crypto Map
Evaluation
Response
Match criterion in an ACE
containing a permit statement
Halt further evaluation of the packet against the remaining ACEs in the
crypto map set, and evaluate the packet security settings against those in
the IKEv1 transform sets or IKEv2 proposals assigned to the crypto
map. After matching the security settings to those in a transform set or
proposal, the ASA applies the associated IPsec settings. Typically for
outbound traffic, this means that it decrypts, authenticates, and routes
the packet.
Match criterion in an ACE
containing a deny statement
Interrupt further evaluation of the packet against the remaining ACEs in
the crypto map under evaluation, and resume evaluation against the
ACEs in the next crypto map, as determined by the next seq-num
assigned to it.
Fail to match all tested permit
ACEs in the crypto map set
Route the packet without encrypting it.
Summary of Contents for 5505 - ASA Firewall Edition Bundle
Page 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Page 61: ...P A R T 1 Getting Started with the ASA ...
Page 62: ......
Page 219: ...P A R T 2 Configuring High Availability and Scalability ...
Page 220: ......
Page 403: ...P A R T 2 Configuring Interfaces ...
Page 404: ......
Page 499: ...P A R T 2 Configuring Basic Settings ...
Page 500: ......
Page 533: ...P A R T 2 Configuring Objects and Access Lists ...
Page 534: ......
Page 601: ...P A R T 2 Configuring IP Routing ...
Page 602: ......
Page 745: ...P A R T 2 Configuring Network Address Translation ...
Page 746: ......
Page 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
Page 846: ......
Page 981: ...P A R T 2 Configuring Access Control ...
Page 982: ......
Page 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
Page 1062: ......
Page 1093: ...P A R T 2 Configuring Application Inspection ...
Page 1094: ......
Page 1191: ...P A R T 2 Configuring Unified Communications ...
Page 1192: ......
Page 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
Page 1334: ......
Page 1379: ...P A R T 2 Configuring Advanced Network Protection ...
Page 1380: ......
Page 1475: ...P A R T 2 Configuring Modules ...
Page 1476: ......
Page 1549: ...P A R T 2 Configuring VPN ...
Page 1550: ......
Page 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
Page 1966: ......
Page 2059: ...P A R T 2 System Administration ...
Page 2060: ......
Page 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
Page 2099: ...P A R T 2 Reference ...
Page 2100: ......