Cisco ASA 5506-X Configuration Manual page 132

Application Layer Protocol Inspection
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How Multiple Traffic Classes are Handled
You can specify multiple inspection class maps or direct matches in the inspection policy map.
If a packet matches multiple different match or class commands, then the order in which the ASA
applies the actions is determined by internal ASA rules, and not by the order they are added to the
inspection policy map. The internal rules are determined by the application type and the logical
progression of parsing a packet, and are not user-configurable. For example for HTTP traffic, parsing a
Request Method field precedes parsing the Header Host Length field; an action for the Request Method
field occurs before the action for the Header Host Length field. For example, the following match
commands can be entered in any order, but the match request method get command is matched first.
match request header host length gt 100
reset
match request method get
log
If an action drops a packet, then no further actions are performed in the inspection policy map. For
example, if the first action is to reset the connection, then it will never match any further match criteria.
If the first action is to log the packet, then a second action, such as resetting the connection, can occur.
If a packet matches multiple match or class commands that are the same, then they are matched in the
order they appear in the policy map. For example, for a packet with the header length of 1001, it will
match the first command below, and be logged, and then will match the second command and be reset.
If you reverse the order of the two match commands, then the packet will be dropped and the connection
reset before it can match the second match command; it will never be logged.
match request header length gt 100
log
match request header length gt 1000
reset
A class map is determined to be the same type as another class map or match command based on the
lowest priority match command in the class map (the priority is based on the internal rules). If a class
map has the same type of lowest priority match command as another class map, then the class maps are
matched according to the order they are added to the policy map. If the lowest priority match for each
class map is different, then the class map with the higher priority match command is matched first. For
example, the following three class maps contain two types of match commands: match request-cmd
(higher priority) and match filename (lower priority). The ftp3 class map includes both commands, but
it is ranked according to the lowest priority command, match filename. The ftp1 class map includes the
highest priority command, so it is matched first, regardless of the order in the policy map. The ftp3 class
map is ranked as being of the same priority as the ftp2 class map, which also contains the match
filename command. They are matched according to the order in the policy map: ftp3 and then ftp2.
class-map type inspect ftp match-all ftp1
match request-cmd get
class-map type inspect ftp match-all ftp2
Cisco ASA Series Firewall CLI Configuration Guide
6-4
HTTP inspection policy maps—If you modify an in-use HTTP inspection policy map (policy-map
type inspect http), you must remove and reapply the inspect http map action for the changes to
take effect. For example, if you modify the "http-map" inspection policy map, you must remove
inspect http http-map command from the layer 3/4 policy, then add it back:
hostname(config)# policy-map test
hostname(config-pmap)# class http
hostname(config-pmap-c)# no inspect http http-map
hostname(config-pmap-c)# inspect http http-map
Chapter 6 Getting Started with Application Layer Protocol Inspection