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Cisco CCNA Certification Exam Tutorial Access List Details You Must KnowTo pass the CCNA exam, you have to be able to write and troubleshoot access lists. As you climb the ladder toward the CCNP and CCIE, you'll see more and more uses for ACLs. Therefore, you had better know the basics! Cisco CCNP BCMSN Exam Tutorial Multicasting And The RPF Check Cisco CCNP / BCMSN Exam Tutorial: Multicasting And The RPF Check Multicasting is a vital topic on your BCMSN, CCNP, and CCIE exams, and it can also be very confusing when you first start studying it... R3(config)#access-list 15 permit any Another often overlooked detail is the order of the lines in an ACL. Even in a two- or three-line ACL, the order of the lines in an ACL is vital. Consider a situation where packets sourced from 172.18.18.0 /24 will be denied, but all others will be permitted. The following ACL would do that. R3#conf t R3(config)#access-list 15 deny 172.18.18.0 0.0.0.255 R3(config)#access-list 15 permit any The previous example also illustrates the importance of configuring the ACL with the lines in the correct order to get the desired results. What would be the result if the lines were reversed? R3#conf t Cisco CCNP BCMSN Exam Tutorial Multicasting And Reserved Addresses Cisco CCNP / BCMSN Exam Tutorial: Multicasting And Reserved Addresses Ever since you picked up your first CCNA book, youve heard about multicasting, gotten a fair idea of what it is, and youve memo.. R3(config)#access-list 15 permit any R3(config)#access-list 15 deny 172.18.18.0 0.0.0.255 If the lines were reversed, traffic from 172.18.18.0 /24 would be matched against the first line of the ACL. The first line is ,permit any", meaning all traffic is permitted. The traffic from 172.18.18.0/24 matches that line, the traffic is permitted, and the ACL stops running. The statement denying the traffic from 172.18.18.0 is never run. The key to writing and troubleshoot access lists is to take just an extra moment to read it over and make sure it's going to do what you intend it to do. It's better to realize your mistake on paper instead of once the ACL's been applied to an interface! Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of freeCCNA andCCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages. You can also join his RSS feed and visit his blog, which is updated several times daily with new Cisco certification articles, free tutorials, and daily CCNA / CCNP exam questions! Details are on the website. For a FREE copy of his latest e-books, ,How To Pass The CCNA, and ,How To Pass The CCNP,, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Get yourCCNA study guide from The Bryant Advantage!
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