Cisco Networking/CCENT/Access Control Lists - Wikiversity. This lesson covers access control lists. Objectives and Skills. Test all router and PC addresses. All tests should be successful. Practice using the following commands. Access Control List Cisco Pdf FilesTest all router and PC addresses. All PC- to- router and router- to- router tests should be successful. The PC- to- PC test should fail. Verify the configuration using the following command. Test all router and PC addresses. All tests should be successful. What Are IP Access Control Lists? Access Control Lists are used in routers to identify and control traffic. Purpose of Access Lists 1. 1000-1099: IPX SAP access list 1100-1199: Extended 48-bit MAC. Allow all other IP traffic. Practice using the following commands. Test all router and PC addresses. All PC- to- router and router- to- router tests should be successful. The PC- to- PC test should fail. Verify the configuration using the following command. Test all router and PC addresses. All tests should be successful. Practice using the following commands. Access Control List Cisco Pdf FileTest all router and PC addresses. All PC- to- router and router- to- router tests should be successful. The PC- to- PC test should fail. Verify the configuration using the following command. Test all router and PC addresses.
All tests should be successful. Allow all other IP traffic. Practice using the following commands. Test all router and PC addresses. All PC- to- router and router- to- router tests should be successful. The PC- to- PC test should fail. Verify the configuration using the following command. Test all router and PC addresses. All tests should be successful. Test the configuration using the following command from both routers. Both connections should be successful. The connection from R1 to R2 should be successful. The connection from R3 to R2 should fail. Test all router and PC addresses. All tests should be successful. Only traffic explicitly permitted by the access list will be allowed. Subnet masks use 1- bits to identify the network. Access list wildcard masks use 1- bits to identify the host addresses to be filtered. Only traffic explicitly permitted by the access list will be allowed. Standard access lists filter based on . Subnet masks use 1- bits to identify . Access list wildcard masks use 1- bits to identify . Subnet masks use 1- bits to identify the network. Access list wildcard masks use 1- bits to identify the host addresses to be filtered. To define an extended IP access list, use. Cisco IOS Security Configuration Guide, Release 1. Access Control Lists: Overview and Guidelines . Access lists can be configured for all routed network protocols (IP, Apple. Talk, and so on) to filter the packets of those protocols as the packets pass through a router. This chapter includes tips, cautions, considerations, recommendations, and general guidelines for how to use access lists. Your router examines each packet to determine whether to forward or drop the packet, on the basis of the criteria you specified within the access lists. Note that sophisticated users can sometimes successfully evade or fool basic access lists because no authentication is required. One of the most important reasons to configure access lists is to provide security for your network, which is the focus of this chapter. If you do not configure access lists on your router, all packets passing through the router could be allowed onto all parts of your network. In Figure 1. 4, host A is allowed to access the Human Resources network, and host B is prevented from accessing the Human Resources network. For example, you can permit e- mail traffic to be routed, but at the same time block all Telnet traffic. You can also use access lists on a router positioned between two parts of your network, to control traffic entering or exiting a specific part of your internal network. This provides a basic buffer from the outside network, or from a less controlled area of your own network into a more sensitive area of your network. You can configure access lists so that inbound traffic or outbound traffic or both are filtered on an interface. In other words, you should define access lists for every protocol enabled on an interface if you want to control traffic flow for that protocol. Note Some protocols refer to access lists as filters. Some type of basic access list should be used with each routed protocol that you have configured for router interfaces. These advanced access lists and features are described in the other chapters within the part . In general, most protocols require at least two basic steps to be accomplished. The first step is to create an access list definition, and the second step is to apply the access list to an interface. For some protocols, you create one access list to filter inbound traffic, and one access list to filter outbound traffic. A single access list can have multiple filtering criteria statements. This approach can considerably simplify maintenance of your access lists. For details, see the . Note Access lists of some protocols must be identified by a name, and access lists of other protocols must be identified by a number. Some protocols can be identified by either a name or a number. When a number is used to identify an access list, the number must be within the specific range of numbers that is valid for the protocol. Table 1. 6 also lists the range of access list numbers that is valid for each protocol. However, each protocol has its own specific set of criteria that can be defined. Each of these statements should reference the same identifying name or number, to tie the statements to the same access list. You can have as many criteria statements as you want, limited only by the available memory. Of course, the more statements you have, the more difficult it will be to comprehend and manage your access lists. Therefore, if a packet does not match any of your criteria statements, the packet will be blocked. Note For most protocols, if you define an inbound access list for traffic filtering, you should include explicit access list criteria statements to permit routing updates. If you do not, you might effectively lose communication from the interface when routing updates are blocked by the implicit . Also note that you cannot delete individual statements after they have been created. You can only delete an entire access list. The order of access list statements is important! When the router is deciding whether to forward or block a packet, the Cisco IOS software tests the packet against each criteria statement in the order in which the statements were created. After a match is found, no more criteria statements are checked. If you need additional statements, you must delete the access list and retype it with the new entries. Then, from your router, use the copy tftp: file. Finally, perform the copy system: running- config nvram: startup- config command to save the access list to your router's NVRAM. Note The first command of an edited access list file should delete the previous access list (for example, type a no access- list command at the beginning of the file). If you do not first delete the previous version of the access list, when you copy the edited file to your router you will merely be appending additional criteria statements to the end of the existing access list. With other protocols, you apply only one access list which checks both inbound and outbound packets. If the packet is permitted, the software continues to process the packet. If the packet is denied, the software discards the packet. If the packet is permitted, the software transmits the packet. If the packet is denied, the software discards the packet. Note Access lists that are applied to interfaces do not filter traffic that originates from that router. The specific instructions for creating access lists and applying them to interfaces vary from protocol to protocol, and this specific information is not included in this chapter. For example, to configure access lists for the IP protocol, refer to the section .
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