Which AS path regular expression will only match a route originating in AS 500 with the last traversing AS of 100?
A.
"$100 .* ^500"
B.
"500 .*"
C.
"^100 .* 500$"
D.
"^100 .*"
Which AS path regular expression will only match a route originating in AS 500 with the last traversing AS of 100?
Which AS path regular expression will only match a route originating in AS 500 with the last traversing AS of 100?
The first indicator that C is wrong is ^. It means starting AS. $means ending AS. A is the correct choice.
BGP AS path is read from right to left meaning the right most AS is the beginning and the left is the final.
http://www.juniper.net/techpubs/en_US/junos9.5/information-products/topic-collections/config-guide-policy/policy-configuring-as-path-regular-expressions-to-use-as-routing-policy-match-conditions.html
“C” has to be correct answer…regular expressions are matched not on the way its read but on how the “show bgp summary” output is displayed.