Specific Recommendations: Access Lists
1. Always start an access-list definition with the privileged command no access-list nnn to clear out any previous versions of access list number nnn.
fumtek(config)# no access-list 51
fumtek(config)# access-list 51 permit host 14.2.9.6
fumtek(config)# access-list 51 deny any log
2. Log access list port messages properly. To ensure that logs contain correct port number information, use the port range arguments shown below at the end of an access list.
access-list 106 deny udp any range 1 65535 any range 1 65535 log
access-list 106 deny tcp any range 1 65535 any range 1 65535 log
access-list 106 deny ip any any log
The last line is necessary to ensure that rejected packets of protocols other than TCP and UDP are properly logged.
3. Enforce traffic address restrictions using access lists. On a border router, allow only internal addresses to enter the router from the internal interfaces, and allow only traffic destined for internal addresses to enter the router from the outside (external interfaces).