I understand what you are saying... But, It was stated that ^300$ will
only match when there is only AS 300 in the AS-Path list and I was
just saying that isn't exactly correct...
On the what ever you would call what I put together below, there are 2
AS's in the list and it still works as stated... Thats all I was
trying to say.
-Adrian
On Oct 20, 2009, at 9:12 PM, Bryan Bartik wrote:
Adrian,
Are we talking about the same thing? While what you say is correct
we are just talking about matching regex. Regardless of the
scenario, _100_ matches 100 anywhere in the path, while ^100$
matches when the path has only 100. Whether or not the route is
allowed because of loop prevention is another issue.
On Tue, Oct 20, 2009 at 3:27 PM, Adrian Brayton <[email protected]>
wrote:
That is not necessarily correct... Sorry about the long winded
explanation!
Lets say you have 3 routers.
A--------B-------C
Router A (AS 100) is advertising 10.1.0.0/24 and 10.1.1.0/24
Router B (AS 200) - aggregate add 10.1.0.0/22 summary-only as-set
Router C (AS300) is advertising 10.1.2.0/24 and 10.1.3.0/24
Now when Router B advertises that summary, its going to have that
summary route and it will look something like this in a "show ip
bgp": Path {100,300}
Now, when it goes to advertise it to its eBGP neighbors... No one
will install that route because both routers (A & C) see there AS in
the path info.
Now, if you were to do this on Router B (Remember, there are 2 AS
paths, {100,300} )
ip as-path access-list 1 permit ^300$
Route-Map BLAH BLAH BLAH
aggregate-address BLAH BLAH
Router A will now have the routes in there because ^300$ was the
only thing permitted when there were "2" as-paths!
I hope you could follow along with what I wrote...
^ Start of string
$ End of string
[] Range of characters
Used to specify range ( i.e. [09] )
( ) 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
Expression Meaning
.* Anything
^$ Locally originated routes
^100_ Learned from AS 100
_100$ Originated in AS 100
_100_ Any instance of AS 100
^[09]+$ Directly connected ASes
On Oct 20, 2009, at 4:09 PM, Joe Astorino wrote:
Also just to add to what Bryan already said the second example says
"it has to start with 100 and then immediately end"...therefore it
would have to have been originated from AS 100. Additionally, like
Bryan said it also means AS 100 is the only AS in the AS_PATH
On Tue, Oct 20, 2009 at 3:15 PM, Syed Zaidi <[email protected]>
wrote:
Whats the difference between.. _100_ and ^100$ , to me both seems
one and the same, however i'm still confused.
Regards,
Syed
_______________________________________________
For more information regarding industry leading CCIE Lab training,
please visit www.ipexpert.com
--
Regards,
Joe Astorino - CCIE #24347 R&S
Technical Instructor - IPexpert, Inc.
Cell: +1.586.212.6107
Fax: +1.810.454.0130
Mailto: [email protected]
_______________________________________________
For more information regarding industry leading CCIE Lab training,
please visit www.ipexpert.com
_______________________________________________
For more information regarding industry leading CCIE Lab training,
please visit www.ipexpert.com
--
Bryan Bartik
CCIE #23707 (R&S), CCNP
Sr. Support Engineer - IPexpert, Inc.
URL: http://www.IPexpert.com
_______________________________________________
For more information regarding industry leading CCIE Lab training, please visit
www.ipexpert.com
