Well there is always an exception to the rule ; ) Regards, Joe Astorino - CCIE #24347 R&S Technical Instructor - IPexpert, Inc. Cell: +1.586.212.6107 Fax: +1.810.454.0130 Mailto: [email protected]
-----Original Message----- From: Adrian Brayton <[email protected]> Date: Tue, 20 Oct 2009 17:27:51 To: Joe Astorino<[email protected]> Cc: Syed Zaidi<[email protected]>; <[email protected]> Subject: Re: [OSL | CCIE_RS] Regex query 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
