Null Security meetup, Delhi, 26 June 2010 More info: https://null.co.in/section/events/meets/page/24/ https://groups.google.com/forum/#!topic/null-co-in/wFuFo3EMY1Y http://packetflows.com

1. ACCESS -LIST

2.  ACLs are lists of conditions used to test
network traffic that tries to travel across a
router interface.These lists tell the router
what types of packets to accept or deny.

3.  The router examines each packet and will
forward or discard it based on the conditions
specified in the ACL.
 An ACL makes routing decisions based on
source address, destination address, protocols,
and upper-layer port numbers.

5. F0/0

6. F0/0/1F0 F0/1
192.168.1.2
192.168.1.3
Inbound
Outbound

8. IP Address Subnet mask Wild card bits
192.168.4.2 255.255.255.0 0.255.255.255
10.0.0.4 0.255.255.255 255.0.0.0
176.19.4.2 255.255.0.0 0.0.255.255

9. Standard
Extended
Dynamic
Reflexive
Time - based

10. All decisions are based on source ip address
Permit or deny whole suite of protocol
Lower processor utilization .

13. Extended ACLs check / required
• source packet addresses
• destination packet addresses
• protocols
• port numbers.
Applied to port closest to source host
It can block port, application, protocols
Valid Range [(100-199) , (2000-2699)]

14. Router(config)# access-list 114 permit tcp 172.16.6.0 0.255.255.255 any equivalent
telnet
Router(config)# access-list 114 permit tcp 172.16.6.0 0.255.255.255 any equivalent ftp
Router(config)# access-list 114 permit tcp 172.16.6.0 0.255.255.255 any equivalent http
Router(config)# interface fastethernet 0/0
Router(config)# ip access-group 114 out
OR
Router(config)# access-list 114 permit tcp 172.16.6.0 0.255.255.255 any equivalent 21
Router(config)# access-list 114 permit tcp 172.16.6.0 0.255.255.255 any equivalent 23
Router(config)# access-list 114 permit tcp 172.16.6.0 0.255.255.255 any equivalent 80
Router(config)# interface fastethernet 0/0
Router(config)# ip access-group 114 out

15. Allows a private local network
to appear as one address to
outside networks like the Internet

17. By:
Anuj Tyagi
wolverinetyagi@yahoo.com