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Chabot College

Chabot College. ELEC 99.08 Extended Access Control Lists. ACL Topics. Extended ACLs Editing ACLs Anatomy of an ACL. Extended ACLs. Provide more precise (finer tuned) packet selection based on: Source and destination addresses Protocols Port numbers 100-199. Steps to Configure ACLs.

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Chabot College

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  1. Chabot College ELEC 99.08 Extended Access Control Lists

  2. ACL Topics • Extended ACLs • Editing ACLs • Anatomy of an ACL

  3. Extended ACLs • Provide more precise (finer tuned) packet selection based on: • Source and destination addresses • Protocols • Port numbers • 100-199

  4. Steps to Configure ACLs 1) Create ACL (global config mode) 2) Apply to an interface (interface config mode)

  5. Extended ACL operation • Permits or denies if all conditions match: • Source Address • Destination Address • Protocol • Port No. or Protocol Options

  6. Extended ACL Syntax Explained • Network Computing has published a great summary chart of the “anatomy of an ACL” • A PDF copy of this chart is on the Semester 2 class page under “Chabot College Study Sheets”

  7. Extended IP ACL command access-listACL-number {permit|deny} protocolsource-ip-addresssource-wildcard-maskdestination-ip-addressdestination-wildcard-maskeqport-number • ACL number: 100-199 • Global Config mode

  8. Extended ACL Example • To permit traffic from the network 192.168.1.0 to the host 192.168.3.10 only on telnet: access-list 101 permit tcp 192.168.1.0 0.0.0.255 192.168.3.10 0.0.0.0 eq 23

  9. Some Protocols with Port Numbers • FTP – 21 • Telnet – 23 • SMTP – 25 • DNS – 53 • TFTP – 69 • WWW, HTML – 80 • POP3 - 110 • SNMP - 161

  10. ACL Configuration Example What will this list do? fre(config)#access-list 101 deny tcp any 192.168.3.10 0.0.0.0 eq 80 fre(config)#access-list 101 permit ip any any fre(config)#int e0 fre(config-if)#ip-access group 101 in fre(config-if)#^z S1 S1 hay oak fre S0 S0 E0 E0 E0 192.168.1.11 192.168.1.0 192.168.2.0 192.168.3.0 192.168.1.10 192.168.2.10 192.168.3.10

  11. ACL Configuration Example What will this list do? fre(config)#access-list 101 deny tcp 192.168.1.10 0.0.0.0 any eq 80 fre(config)#access-list 101 deny tcp 192.168.1.0 0.0.0.255 any eq 21 fre(config)#access-list 101 permit ip any any fre(config)#int e0 fre(config-if)#ip-access group 101 in fre(config-if)#^z S1 S1 hay oak fre S0 S0 E0 E0 E0 192.168.1.11 192.168.1.0 192.168.2.0 192.168.3.0 192.168.1.10 192.168.2.10 192.168.3.10

  12. ACL Configuration Example What will this list do? (What’s wrong here?) fre(config)#access-list 101 deny tcp 192.168.1.10 0.0.0.0 any eq 80 fre(config)#int e0 fre(config-if)#ip-access group 101 in fre(config-if)#^z S1 S1 hay oak fre S0 S0 E0 E0 E0 192.168.1.11 192.168.1.0 192.168.2.0 192.168.3.0 192.168.1.10 192.168.2.10 192.168.3.10

  13. Extended ACL Placement Blocking traffic from Fremont LAN to Oakland PC Place extended ACL close to source. fre(config)#access-list 101 deny ip any host 192.168.3.10 fre(config)#access-list 101 permit ip any any fre(config)#int e0 fre(config-if)#ip-access group 101 in S1 S1 hay oak fre S0 S0 E0 E0 E0 192.168.1.11 192.168.1.0 192.168.2.0 192.168.3.0 192.168.1.10 192.168.2.10 192.168.3.10

  14. Standard ACL Placement Blocking traffic from Fremont LAN to Oakland LAN Place standard ACL close to destination. oak(config)#access-list 10 deny 192.168.1.0 0.0.0.255 oak(config)#access-list 10 permit any oak(config)#int e0 oak(config-if)#ip-access group 10 out S1 S1 hay oak fre S0 S0 E0 E0 E0 192.168.1.11 192.168.1.0 192.168.2.0 192.168.3.0 192.168.1.10 192.168.2.10 192.168.3.10

  15. ACL Placement Blocking traffic from Fremont LAN to Oakland PC Standard or Extended ACL Which seems more efficient? Why? Extended Standard S1 S1 hay oak fre S0 S0 E0 E0 E0 192.168.1.11 192.168.1.0 192.168.2.0 192.168.3.0 192.168.1.10 192.168.2.10 192.168.3.10

  16. Editing ACLs • The exec adds new lines (rules) to an ACL at the end; probably not where you want them. • To change lines in the middle, you must delete the entire list and re-enter it. • Or - dump your config out to a text file & edit it as follows:

  17. Editing ACLs • Use Hyperterm’s “capture text” to save the config as a text file.. • In your editor, renumber the existing ACL using search & replace. • Edit the renumbered ACL. • Paste the new ACL into your running config. • On the interface where the old ACL is applied, apply the new list with the command: ip access-group XXX in/out (Make XXX the new ACL number; the old list will automatically be turned off when you turn on the new list. If you encounter problems with the new list, you can re-apply the old one with the ip-access group command.)

  18. ACL Syntax Summary • Network Computing has published a great summary chart of the “anatomy of an ACL” • There is a link to this chart on the Semester 2 class page under “Chabot College Study Sheets”.

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