The ABCs of TCP/IP, 2nd Edition

Enhancing Security 227

Note that one would use a name in the access-group command to reference

a named access list. Also note that one would use either in or out to reference

the direction with respect to the router interface where filtering occurs. Because

the access-group command only associates the direction of filtering to an

access list number or name, one would use an interface command before

the access-group command to tie everything to an interface. For example,

assume one wants to apply the extended IP access list named “inbound”

previously created to a router’s serial port in the inbound direction. The

statements would be as follows:

interface serial 0

ip access-group inbound in

!

ip access-list extended inbound

permit tcp any any established

permit ...