Cisco Cisco ACE Application Control Engine Module

The new “\xST” metacharacter has the following usage guidelines related to its inclusion in regex 
matching: 

If the input matches a regex pattern that includes the “\xST” metacharacter, the regex engine will 
halt upon finding the character directly next to the '\xST' in the regex string (2nd '\x01' in the match 
statement). 

No additional input data will be considered by the ACE once the matching pattern is seen which may 
affect other regexes that are configured elsewhere in the policy. In this case, the “\xST” 
metacharacter should be used only once in the policy. 

The “\xST” metacharacter should only be used at the end of a regex pattern and not at the beginning. 
In this case, the ACE will display the “Error: Invalid regular expression” error message.

The “\xST” metacharacter should not be added directly after a * wildcard match. For example, 
“abc.*\xST” would not be a recommended regex.

The following configuration examples show the use of the “\xST” metacharacter in two very specific 
regexes:

parameter-map type generic SESSID-PARAM

  set max-parse-length 76

sticky layer4-payload SESSID-STICKY

  serverfarm SF1

  response sticky

  layer4-payload offset 43 length 32 begin-pattern "(\x20|\x00\xST)"

sticky layer4-payload FIX-STICKY

  serverfarm FIX-SF1

  layer4-payload begin-pattern "\x0149=" end-pattern "\x01"

class-map type generic match-all FIX-CM

  2 match layer4-payload regex ".*\x0110=...\x01\xST"