Alot of people seem to struggle with BGP regular expressions so I put them together the following questions
Here are a list of AS paths (I just threw them together so we can create regular expressions). The AS that you are in is AS1.
100 110 2009 20093 20100 54 321
100 110 2009 20111 129 22 10
10 200 19 24 39 4 32
16 100 888 1339 2
Create a regular expression that filters routes that originate in AS321
Create a regular expression that filters routes that have instances of AS200 in the path
Create a regular expression that filters routes that are learned from AS10
Create a regular expression that filters routes that are locally originated
Create a regular expression that filters all routes from any AS
Create a regular expression that filters routes that pass through AS39
Create a regular expression that filters routes that have a number "20" anywhere within the AS number or path
Regular Expressions and their usage
^
Start of string
$
End of string
[]
Range of characters
-
Used to specify range ( i.e. [0-9] )
( )
Logical grouping
.
Any single character
*
Zero or more instances
+
One or more instance
?
Zero or one instance
_
Comma, open or close brace, open or close parentheses, start or end of string, or space
Have fun!
