© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE I Chapter 6 1 Access Control Lists Accessing the WAN – Chapter 5

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 2 Objectives  Explain how ACLs are used to secure a medium-size Enterprise branch office network.  Configure standard ACLs in a medium-size Enterprise branch office network.  Configure extended ACLs in a medium-size Enterprise branch office network.  Describe complex ACLs in a medium-size Enterprise branch office network.  Implement, verify and troubleshoot ACLs in an enterprise network environment.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 3 What is ACL? Access Control List stands for the list of packet filter rules, that defines, whether to allow or deny specified type of communication. It does similar actions like complex Firewalls.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 4 ACL rules  ACL is the list of the rules, which starts at the top of the list and ends with the first match (Lunch example) AllowRice AllowPotato DenyHamburger AllowTomato AllowHamburger DenyTomato Can I eat Potato? First matching rule is on line 2 - ALLOW Can I eat Hamburger? First matching rule is on line 3 - DENY Anything not mentioned here DENY Can I eat Tomato? First matching rule is on line 4 - ALLOW Can I eat Ham? Implicit rule at the end of the list - DENY

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 5 Explain How ACLs are Used to Secure a Medium-Size Enterprise Branch Office Network  Explain how a packet filter allows or blocks traffic

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 6 Explain How ACLs are Used to Secure a Medium-Size Enterprise Branch Office Network  Describe how ACLs control access to networks

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 7 ACL Types extendedstandard numbered named extendedstandard Standard – decision made only by source host/network address Extended – decision made by complex criteria: source or destination host/network address protocol used in case of TCP/UDP – service that is used (port)

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 8 Explain How ACLs are Used to Secure a Medium-Size Enterprise Branch Office Network  Explain how Cisco ACLs can be identified using standardized numbering or names

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 9 ACL syntax Before we start writing rules, we need to understand the term wildcard mask ! Wildcard mask – tells us, which part of IP address is necessary to check with corresponding IP address 0-bit in wildcard mask represent bit, that needs to be checked 1-bit in wildcard mask represent bit, that can be ignored Example: Wildcard mask: in binary Tells us, that first 24 bits of IP address needs to be checked.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 10 Lets do the practise… Which bits of IP address needs to be checked, when we want to be sure, that IP address has in last octet number between ? Examples: They all begin with 25 th bit set to 1 in order to be greater than – – – – Wildcard mask:

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 11 Lets do the practise… Which bits of IP address needs to be checked, when we want to be sure, that IP address has in last octet number between ? Examples: They all begin with 25 th bit set to 1 in order to be greater than – – – – Wildcard mask: It is not enough, because we need to say what value of that checked bit we expect! (in our case, we expect 1) Wildcard mask is everytime paired with an IP address as refference for bit values

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 12 Second trial… Which combination of IP and Wildcard mask we need to use when we want to check, whether packet has address from address space /24 and has even number between in last octet? Examples: Wildcard mask: It is not necessary to check any bits Which bits needs to be checked, so we will be sure, it is from /24 Wildcard mask: Check first 24 bits of IP address Which bits we need to check, so we will be sure, it is the number between in last octet Wildcard mask: Check first 25 bits of IP address Which bits we need to check, so we will be sure, it is the even number in last octet? Wildcard mask: Check first 25 bits of IP address and 32 nd bit Wildcard: Coresponding IP: e.g

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 13 Numbered ACL

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 14 Configure Standard ACLs in a Medium- Size Enterprise Branch Office Network  Explain the process for editing numbered ACLs

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 15 Named ACL

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 16 Configure Standard ACLs in a Medium- Size Enterprise Branch Office Network  Describe how to monitor and verify ACLs

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 17 Configure Extended ACLs in a Medium- Size Enterprise Branch Office Network  Describe how to apply an extended ACL to an interface

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 18 Configure Extended ACLs in a Medium- Size Enterprise Branch Office Network  Describe how to create named extended ACLs

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 19 Describe Complex ACLs in a Medium-Size Enterprise Branch Office Network  List the three types of complex ACLs

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 20 Describe Complex ACLs in a Medium-Size Enterprise Branch Office Network  Explain how and when to use dynamic ACLs

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 21 Describe Complex ACLs in a Medium-Size Enterprise Branch Office Network  Explain how and when to use reflexive ACLs

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 22 Describe Complex ACLs in a Medium-Size Enterprise Branch Office Network  Explain how and when to use time-based ACLs

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 23 Describe Complex ACLs in a Medium-Size Enterprise Branch Office Network  Describe how to troubleshoot common ACL problems

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 24 Implement, Verify and Troubleshoot ACLs in an Enterprise Network Environment  Create, place and verify a standard/ extended ACL and verify its placement.  Verify ACL’s functionality and troubleshoot as needed.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 25 Summary  An Access List (ACL) is: A series of permit and deny statements that are used to filter traffic  Standard ACL –Identified by numbers and –Filter traffic based on source IP address  Extended ACL –Identified by number & –Filter traffic based on Source IP address Destination IP address Protocol Port number

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 26 Summary  Named ACL –Used with IOS 11.2 and above –Can be used for either standard or extended ACL  ACL’s use Wildcard Masks (WCM) –Described as the inverse of a subnet mask Reason –0  check the bit –1  ignore the bit

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 27 Summary  Implementing ACLs –1 st create the ACL –2 nd place the ACL on an interface Standard ACL are placed nearest the destination Extended ACL are placed nearest the source  Use the following commands for verifying & troubleshooting an ACL –Show access-list –Show interfaces –Show run

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 28 Summary  Complex ACL –Dynamic ACL –Reflexive ACL –Time based ACL

© 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 29