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ACL(Access Control Lists)

ACL(Access Control Lists). Standard , Extended and Named ACL. Objectives. In this lesson, you will learn: Purpose of ACLs Its application to an enterprise network How ACLs are used to control access Types of Cisco ACLs. Standard ACL Extended ACL Named ACL. ACL (Access Control Lists).

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ACL(Access Control Lists)

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  1. ACL(Access Control Lists) Standard , Extended and Named ACL

  2. Objectives • In this lesson, you will learn: • Purpose of ACLs • Its application to an enterprise network • How ACLs are used to control access • Types of Cisco ACLs. • Standard ACL • Extended ACL • Named ACL

  3. ACL (Access Control Lists) Allow Email/Deny Telnet • An ACL is a router configuration script that controls whether a router permits or denies packets • By default, a router does not have any ACLs configured and therefore does not filter traffic. No video to S1 No access to S2 for S1 No FTP No web

  4. Types of ACL • These are examples of IP ACLs that can be configured in Cisco IOS Software: • Standard ACLs • Extended ACLs • IP-named ACLs • And Others

  5. Where to apply ACL - Guidelines for using ACLs Allow Email/Deny Telnet • Use ACLs in firewall routers positioned between internal network and an external network • Use ACLs on a router positioned between two parts of your network to control traffic entering or exiting a specific part of your internal network. • Configure ACLs on border routers, the routers situated at the edges of your networks to act as a buffer from the outside network No video to S1 No access to S2 for S1 No FTP No web

  6. Testing Packets with ACLs • Configure ACL Example: Permit traffic from a particular host 192.5.5.10 • Router(config)#access-list 1permit 192.5.5.10 0.0.0.0 • Router(config)# access-list 1 deny any • Wild card mask • A wildcard mask is written to tell the router what bits in the address to match and what bits to ignore. • A “0” bit means means check this bit position. A “1” means ignore this bit position. • Note:Notice that this wildcard mask is a mirror image of the subnet mask for the address • Apply to appropriate router interface • In or out • Example: Router(config-if)# ip access-group 1 in Wild card mask IP mask

  7. Practice Wild card masks • Write a wildcard mask for all hosts in 192.168.20.0 subnet • Write a wildcard mask for all hosts in 10.10.0.0 • Write a wildcard mask for the host 192.168.1.100

  8. Masking Practice • Write an ip mask and wildcard mask for the subnet 172.16.128.0 with a subnet mask of 255.255.128.0? • Answer: 172.16.128.0 0.0.127.255 • Write an ip mask and wildcard mask for the subnet 10.0.8.0 with a subnet mask of 255.255.248.0? • Answer: 10.0.8.0 0.0.7.255

  9. ACL Operation - Inbound ACLs ACL statements operate in sequential order. If a packet header and an ACL statement match, the rest of the statements in the list are skipped If a packet header does not match an statement, the packet is tested against the next statement in the list. A final implied (IMPLICIT DENY) statement covers all packets for which conditions did not test true.

  10. Placement of Standard ACL # access-list 99 deny 192.168.10.0 0.0.0.255 # access-list 99 permit any R3(config)#interface serial 0/0/1 R3(config-if)# ip access-group 1 in

  11. Extended ACL • Extended ACLs • Filter IP packets based on several attributes: • protocol type, • source and IP address, destination IP address, • source TCP or UDP ports, destination TCP or UDP ports • Example: ACL 102 deny FTP and Telnet traffic originating from any address on the 192.168.10.0/24 from leaving the network

  12. Placement of ACLs - Extended. Access-list 102 deny tcp 192.168.10.0 0.0.0.255 any eq telnet Access-list 102 deny tcp 192.168.10.0 0.0.0.255 any eq ftp Access-list 102 permit any Apply access list ‘inbound’ to Fa 0/1 interface of R1 R1(config)# interface fa 0/1 R1(config-if)# ip access-group 102 in

  13. What does the following ACL do? Access-list 1 permit any Access-list 1 deny host 10.1.1.1 Access-list 1 deny any Access-list 1 deny host 10.1.1.1 Access-list 1 deny 192.168.1.0 0.0.0.255

  14. Commenting ACLs

  15. Named ACL

  16. Extended NACLs

  17. Editing named ACLs

  18. Example NetworkControlling inbound access • Deny all traffic from private IP address • Allow all IP sessions already established with the ack bit turned. • deny anyone from entering your network from the outside with an internal address (spoofing your network) and log each packet occurrence. • deny the infamous Donald Dick and Prosiak ports. • deny the Deepthroat and Sockets des Troie ports. • deny any snmp requests from the outside. SNMP is a valuable tool to hackers for network discovery. • permits packets that were not previously rejected to enter your network.

  19. Example:Inbound access control list • access-list 100 deny ip 10.0.0.0 0.255.255.255 any log • access-list 100 deny ip 172.16.0.0 0.15.255.255 any log • access-list 100 deny ip 192.168.0.0 0.0.255.255 any log • access-list 100 deny ip any host 127.0.0.1 log • access-list 100 permit ip any est • access-list 100 deny ip < network IP address> <your network mask> any log • access-list 100 deny tcp any any eq 22222 log • access-list 100 deny tcp any any range 60000 60020 log • access-list 100 deny udp any any eq snmp log • access-list 100 permit ip any any Administrative PC inbound traffic Perimeter router Administrative PC

  20. Explaining commands • Entry 5—“permit ip any [your network IP address] [your network mask] est”—automatically allows all IP sessions already established with the ack bit turned. The purpose of this entry is to ensure that if your firewall allows a connection request to leave your network, the router doesn’t stop its return. • Entry 6—“deny ip [your network IP address] [your network mask] any log”—denies anyone from entering your network from the outside with an internal address (spoofing your network) and logs each packet occurrence. This is very important for good security. • Entry 7—“deny tcp any anyeq 22222 log”—denies the infamous Donald Dick and Prosiak ports. • Entry 8—“deny tcp any any range 60000 60020 log”—denies the Deepthroat and Sockets des Troie ports. • Entry 9—“deny udp any anyeqsnmp log”—denies any snmp requests from the outside. SNMP is a valuable tool to hackers for network discovery. • Entry 10—“permit ip any any”—permits packets that were not previously rejected to enter your network.

  21. Monitoring and verifying ACLs

  22. Task: Configure standard and Extended ACL

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