Cisco ENSA Module 5: ACLs for IPv4 Configuration PDF

17/08/2022 Module 5: ACLs for IPv4 Configuration Enterprise Networking, Security, and Automation v7.0 (ENSA) 1...

17/08/2022 Module 5: ACLs for IPv4 Configuration Enterprise Networking, Security, and Automation v7.0 (ENSA) 1 OFFICIAL Module Objectives Module Title: ACLs for IPv4 Configuration Module Objective: Implement IPv4 ACLs to filter traffic and secure administrative access. Topic Title Topic Objective Configure Standard IPv4 ACLs Configure standard IPv4 ACLs to filter traffic to meet networking requirements. Modify IPv4 ACLs Use sequence numbers to edit existing standard IPv4 ACLs. Secure VTY Ports with a Standard IPv4 ACL Configure a standard ACL to secure VTY access. Configure Extended IPv4 ACLs Configure extended IPv4 ACLs to filter traffic according to networking requirements. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2 OFFICIAL 2 1  17/08/2022 5.1 Configure Standard IPv4 ACLs © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 3 OFFICIAL Configure Standard IPv4 ACLs Create an ACL All access control lists (ACLs) must be planned. When configuring a complex ACL, it is suggested that you: Use a text editor and write out the specifics of the policy to be implemented. Add the IOS configuration commands to accomplish those tasks. Include remarks to document the ACL. Copy and paste the commands onto the device. Always thoroughly test an ACL to ensure that it correctly applies the desired policy. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4 OFFICIAL 4 2  17/08/2022 OFFICIAL Configure Standard IPv4 ACLs Numbered Standard IPv4 ACL Syntax To create a numbered standard ACL, use the access-list command. Parameter Description access-list-number Number range is 1 to 99 or 1300 to 1999 deny Denies access if the condition is matched permit Permits access if the condition is matched remark text (Optional) text entry for documentation purposes source Identifies the source network or host address to filter source-wildcard (Optional) 32-bit wildcard mask that is applied to the source log (Optional) Generates and sends an informational message when the ACE is matched Note: Use the no access-list access-list-number global configuration command to remove a numbered standard ACL. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5 OFFICIAL 5 OFFICIAL Configure Standard IPv4 ACLs Named Standard IPv4 ACL Syntax To create a named standard ACL, use the ip access-list standard command. ACL names are alphanumeric, case sensitive, and must be unique. Capitalizing ACL names is not required but makes them stand out when viewing the running-config output. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6 OFFICIAL 6 3  17/08/2022 OFFICIAL Configure Standard IPv4 ACLs Apply a Standard IPv4 ACL After a standard IPv4 ACL is configured, it must be linked to an interface or feature. The ip access-group command is used to bind a numbered or named standard IPv4 ACL to an interface. To remove an ACL from an interface, first enter the no ip access-group interface configuration command. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 7 OFFICIAL 7 OFFICIAL Configure Standard IPv4 ACLs Numbered Standard ACL Example The example ACL permits traffic from host 192.168.10.10 and all hosts on the 192.168.20.0/24 network out interface serial 0/1/0 on router R1. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 8 OFFICIAL 8 4  17/08/2022 OFFICIAL Configure Standard IPv4 ACLs Numbered Standard ACL Example (Cont.) Use the show running-config command to review the ACL in the configuration. Use the show ip interface command to verify the ACL is applied to the interface. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9 OFFICIAL 9 OFFICIAL Configure Standard IPv4 ACLs Named Standard ACL Example The example ACL permits traffic from host 192.168.10.10 and all hosts on the 192.168.20.0/24 network out interface serial 0/1/0 on router R1. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 10 OFFICIAL 10 5  17/08/2022 OFFICIAL Configure Standard IPv4 ACLs Named Standard ACL Example (Cont.) Use the show access-list command to review the ACL in the configuration. Use the show ip interface command to verify the ACL is applied to the interface. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11 OFFICIAL 11 OFFICIAL Configure Standard IPv4 ACLs Packet Tracer – Configure Numbered Standard IPv4 ACLs In this Packet Tracer, you will complete the following objectives: Plan an ACL Implementation. Configure, Apply, and Verify a Standard ACL. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12 OFFICIAL 12 6  17/08/2022 OFFICIAL Configure Standard IPv4 ACLs Packet Tracer – Configure Named Standard IPv4 ACLs In this Packet Tracer, you will complete the following objectives: Configure and Apply a Named Standard ACL. Verify the ACL Implementation. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 13 OFFICIAL 13 5.2 Modify IPv4 ACLs © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 14 14 7  17/08/2022 OFFICIAL Modify IPv4 ACLs Two Methods to Modify an ACL After an ACL is configured, it may need to be modified. ACLs with multiple ACEs can be complex to configure. Sometimes the configured ACE does not yield the expected behaviors. There are two methods to use when modifying an ACL: Use a text editor. Use sequence numbers. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 15 OFFICIAL 15 OFFICIAL Modify IPv4 ACLs Text Editor Method ACLs with multiple ACEs should be created in a text editor. This allows you to plan the required ACEs, create the ACL, and then paste it into the router interface. It also simplifies the tasks to edit and fix an ACL. To correct an error in an ACL: Copy the ACL from the running configuration and paste it into the text editor. Make the necessary edits or changes. Remove the previously configured ACL on the router. Copy and paste the edited ACL back to the router. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 16 OFFICIAL 16 8  17/08/2022 OFFICIAL Modify IPv4 ACLs Sequence Number Method An ACL ACE can be deleted or added using the ACL sequence numbers. Use the ip access-list standard command to edit an ACL. Statements cannot be overwritten using an existing sequence number. The current statement must be deleted first with the no 10 command. Then the correct ACE can be added using sequence number. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 17 OFFICIAL 17 OFFICIAL Modify IPv4 ACLs Modify a Named ACL Example Named ACLs can also use sequence numbers to delete and add ACEs. In the example an ACE is added to deny hosts 192.168.10.11. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 18 OFFICIAL 18 9  17/08/2022 OFFICIAL Modify IPv4 ACLs ACL Statistics The show access-lists command in the example shows statistics for each statement that has been matched. The deny ACE has been matched 20 times and the permit ACE has been matched 64 times. Note that the implied deny any statement does not display any statistics. To track how many implicit denied packets have been matched, you must manually configure the deny any command. Use the clear access-list counters command to clear the ACL statistics. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 19 OFFICIAL 19 OFFICIAL Modify IPv4 ACLs Packet Tracer – Configure and Modify Standard IPv4 ACLs In this Packet Tracer, you will complete the following objectives: Configure Devices and Verify Connectivity. Configure and Verify Standard Numbered and Named ACLs. Modify a Standard ACL. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 20 OFFICIAL 20 10  17/08/2022 5.3 Secure VTY Ports with a Standard IPv4 ACL © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 21 21 OFFICIAL Secure VTY Ports with a Standard IPv4 ACL The access-class Command A standard ACL can secure remote administrative access to a device using the vty lines by implementing the following two steps: Create an ACL to identify which administrative hosts should be allowed remote access. Apply the ACL to incoming traffic on the vty lines. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 22 OFFICIAL 22 11  17/08/2022 OFFICIAL Secure VTY Ports with a Standard IPv4 ACL Secure VTY Access Example This example demonstrates how to configure an ACL to filter vty traffic. First, a local database entry for a user ADMIN and password class is configured. The vty lines on R1 are configured to use the local database for authentication, permit SSH traffic, and use the ADMIN-HOST ACL to restrict traffic. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 23 OFFICIAL 23 OFFICIAL Secure VTY Ports with a Standard IPv4 ACL Verify the VTY Port is Secured After an ACL to restrict access to the vty lines is configured, it is important to verify it works as expected. To verify the ACL statistics, issue the show access-lists command. The match in the permit line of the output is a result of a successful SSH connection by host with IP address 192.168.10.10. The match in the deny statement is due to the failed attempt to create a SSH connection from a device on another network. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 24 OFFICIAL 24 12  17/08/2022 5.4 Configure Extended IPv4 ACLs © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 25 25 OFFICIAL Configure Extended IPv4 ACLs Extended ACLs Extended ACLs provide a greater degree of control. They can filter on source address, destination address, protocol (i.e., IP, TCP, UDP, ICMP), and port number. Extended ACLs can be created as: Numbered Extended ACL - Created using the access-list access-list-number global configuration command. Named Extended ACL - Created using the ip access-list extended access-list- name. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 26 OFFICIAL 26 13  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Protocols and Ports Protocol Options Extended ACLs can filter on internet protocols and ports. Use the ? to get help when entering a complex ACE. The four highlighted protocols are the most popular options. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 27 OFFICIAL 27 OFFICIAL Configure Extended IPv4 ACLs Protocols and Ports (Cont.) Selecting a protocol influences port options. Many TCP port options are available, as shown in the output. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 28 OFFICIAL 28 14  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Protocols and Port Numbers Configuration Examples Extended ACLs can filter on different port number and port name options. This example configures an extended ACL 100 to filter HTTP traffic. The first ACE uses the www port name. The second ACE uses the port number 80. Both ACEs achieve exactly the same result. Configuring the port number is required when there is not a specific protocol name listed such as SSH (port number 22) or an HTTPS (port number 443), as shown in the next example. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 29 OFFICIAL 29 OFFICIAL Configure Extended IPv4 ACLs Apply a Numbered Extended IPv4 ACL In this example, the ACL permits both HTTP and HTTPS traffic from the 192.168.10.0 network to go to any destination. Extended ACLs can be applied in various locations. However, they are commonly applied close to the source. Here ACL 110 is applied inbound on the R1 G0/0/0 interface. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 30 OFFICIAL 30 15  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs TCP Established Extended ACL TCP can also perform basic stateful firewall services using the TCP established keyword. The established keyword enables inside traffic to exit the inside private network and permits the returning reply traffic to enter the inside private network. TCP traffic generated by an outside host and attempting to communicate with an inside host is denied. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 31 OFFICIAL 31 OFFICIAL Configure Extended IPv4 ACLs TCP Established Extended ACL (Cont.) ACL 120 is configured to only permit returning web traffic to the inside hosts. The ACL is then applied outbound on the R1 G0/0/0 interface. The show access-lists command shows that inside hosts are accessing the secure web resources from the internet. Note: A match occurs if the returning TCP segment has the ACK or reset (RST) flag bits set, indicating that the packet belongs to an existing connection. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 32 OFFICIAL 32 16  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Named Extended IPv4 ACL Syntax Naming an ACL makes it easier to understand its function. To create a named extended ACL, use the ip access-list extended configuration command. In the example, a named extended ACL called NO-FTP-ACCESS is created and the prompt changed to named extended ACL configuration mode. ACE statements are entered in the named extended ACL sub configuration mode. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 33 OFFICIAL 33 OFFICIAL Configure Extended IPv4 ACLs Named Extended IPv4 ACL Example The topology below is used to demonstrate configuring and applying two named extended IPv4 ACLs to an interface: SURFING - This will permit inside HTTP and HTTPS traffic to exit to the internet. BROWSING - This will only permit returning web traffic to the inside hosts while all other traffic exiting the R1 G0/0/0 interface is implicitly denied. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 34 OFFICIAL 34 17  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Named Extended IPv4 ACL Example (Cont.) The SURFING ACL permits HTTP and HTTPS traffic from inside users to exit the G0/0/1 interface connected to the internet. Web traffic returning from the internet is permitted back into the inside private network by the BROWSING ACL. The SURFING ACL is applied inbound and the BROWSING ACL is applied outbound on the R1 G0/0/0 interface. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 35 OFFICIAL 35 OFFICIAL Configure Extended IPv4 ACLs Named Extended IPv4 ACL Example (Cont.) The show access-lists command is used to verify the ACL statistics. Notice that the permit secure HTTPS counters (i.e., eq 443) in the SURFING ACL and the return established counters in the BROWSING ACL have increased. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 36 OFFICIAL 36 18  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Edit Extended ACLs An extended ACL can be edited using a text editor when many changes are required. Or, if the edit applies to one or two ACEs, then sequence numbers can be used. Example: The ACE sequence number 10 in the SURFING ACL has an incorrect source IP networks address. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 37 OFFICIAL 37 OFFICIAL Configure Extended IPv4 ACLs Edit Extended ACLs (Cont.) To correct this error the original statement is removed with the no sequence_# command and the corrected statement is added replacing the original statement. The show access-lists command output verifies the configuration change. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 38 OFFICIAL 38 19  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Another Extended IPv4 ACL Example Two named extended ACLs will be created: PERMIT-PC1 - This will only permit PC1 TCP access to the internet and deny all other hosts in the private network. REPLY-PC1 - This will only permit specified returning TCP traffic to PC1 implicitly deny all other traffic. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 39 OFFICIAL 39 OFFICIAL Configure Extended IPv4 ACLs Another Extended IPv4 ACL Example (Cont.) The PERMIT-PC1 ACL permits PC1 (192.168.10.10) TCP access to the FTP, SSH, Telnet, DNS , HTTP, and HTTPS traffic. The REPLY-PC1 ACL will permit return traffic to PC1. The PERMIT-PC1 ACL is applied inbound and the REPLY-PC1 ACL applied outbound on the R1 G0/0/0 interface. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 40 OFFICIAL 40 20  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Verify Extended ACLs The show ip interface command is used to verify the ACL on the interface and the direction in which it was applied. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 41 OFFICIAL 41 OFFICIAL Configure Extended IPv4 ACLs Verify Extended ACLs (Cont.) The show access-lists command can be used to confirm that the ACLs work as expected. The command displays statistic counters that increase whenever an ACE is matched. Note: Traffic must be generated to verify the operation of the ACL. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 42 OFFICIAL 42 21  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Verify Extended ACLs (Cont.) The show running-config command can be used to validate what was configured. The command also displays configured remarks. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 43 OFFICIAL 43 OFFICIAL Configure Extended IPv4 ACLs Packet Tracer – Configure Extended IPv4 ACLs - Scenario 1 In this Packet Tracer, you will complete the following objectives: Configure, Apply, and Verify an Extended Numbered IPv4 ACL. Configure, Apply, and Verify an Extended Named IPv4 ACL. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 44 OFFICIAL 44 22  17/08/2022 OFFICIAL Configure Extended IPv4 ACLs Packet Tracer – Configure Extended IPv4 ACLs - Scenario 2 In this Packet Tracer, you will complete the following objectives: Configure a Named Extended IPv4 ACL. Apply and Verify the Extended IPv4 ACL. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 45 OFFICIAL 45 5.5 Module Practice and Quiz © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 46 46 23  17/08/2022 OFFICIAL Module Practice and Quiz Packet Tracer – IPv4 ACL Implementation Challenge In this Packet Tracer, you will complete the following objectives: Configure a router with standard named ACLs Configure a router with extended named ACLs Configure a router with extended ACLs to meet specific communication requirements Configure an ACL to control access to network device terminal lines Configure the appropriate router interfaces with ACLs in the appropriate direction Verify the operation of the configured ACLs © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 47 OFFICIAL 47 OFFICIAL Module Practice and Quiz Lab – Configure and Verify Extended IPv4 ACLs In this lab, you will complete the following objectives: Build the Network and Configure Basic Device Settings Configure and Verify Extended IPv4 ACLs © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 48 OFFICIAL 48 24  17/08/2022 OFFICIAL Module Practice and Quiz What did I learn in this module? To create a numbered standard ACL, use the use the ip access-list standard access-list- name global configuration command. Use the no access-list access-list-number global configuration command to remove a numbered standard ACL. Use the show ip interface command to verify if an interface has an ACL applied to it. To create a named standard ACL, use the ip access-list standard access-list-name global configuration command. Use the no ip access-list standard access-list-name global configuration command to remove a named standard IPv4 ACL. To bind a numbered or named standard IPv4 ACL to an interface, use the ip access-group {access-list-number | access-list-name} { in | out } global configuration command. To remove an ACL from an interface, first enter the no ip access-group interface configuration command. To remove the ACL from the router, use the no access-list global configuration command. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 49 OFFICIAL 49 OFFICIAL Module Practice and Quiz What did I learn in this module? Extended ACLs can filter on source address, destination address, protocol (i.e., IP, TCP, UDP, ICMP), and port number. To create a numbered extended ACL, use the Router(config)# access-list access-list-number {deny | permit | remark text} protocol source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [established] [log] global configuration command. ALCs can also perform basic stateful firewall services using the TCP established keyword. The show ip interface command is used to verify the ACL on the interface and the direction in which it was applied. To modify an ACL, use a text editor or use sequence numbers. An ACL ACE can also be deleted or added using the ACL sequence numbers. Sequence numbers are automatically assigned when an ACE is entered. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 50 OFFICIAL 50 25  17/08/2022 Module 5: ACLs for IPv4 Configuration OFFICIAL New Terms and Commands numbered extended ACL named extended ACL numbered standard ACL named standard ACL ip access-list standard no ip access-list standard ip access-list extended ip access-list ip access-group show access-lists clear access-list counters access-class established © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 51 OFFICIAL 51 52 26