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
_______________________________________________
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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
