Chapter 1
Configuring Network Security with ACLs
In this example, the network is a Class B network with the address 128.88.0.0, and the mail host address
is 128.88.1.2. The established keyword is used only for the TCP to show an established connection. A
match occurs if the TCP datagram has the ACK or RST bits set, which show that the packet belongs to
an existing connection. Gigabit Ethernet interface 1 on stack member 1 is the interface that connects the
router to the Internet.
Switch(config)# access-list 102 permit tcp any 128.88.0.0 0.0.255.255 established
Switch(config)# access-list 102 permit tcp any host 128.88.1.2 eq 25
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# ip access-group 102 in
Named ACLs
This example creates a standard ACL named internet_filter and an extended ACL named
marketing_group. The internet_filter ACL allows all traffic from the source address 1.2.3.4.
Switch(config)# ip access-list standard Internet_filter
Switch(config-ext-nacl)# permit 1.2.3.4
Switch(config-ext-nacl)# exit
The marketing_group ACL allows any TCP Telnet traffic to the destination address and wildcard
171.69.0.0 0.0.255.255 and denies any other TCP traffic. It permits ICMP traffic, denies UDP traffic
from any source to the destination address range 171.69.0.0 through 179.69.255.255 with a destination
port less than 1024, denies any other IP traffic, and provides a log of the result.
Switch(config)# ip access-list extended marketing_group
Switch(config-ext-nacl)# permit tcp any 171.69.0.0 0.0.255.255 eq telnet
Switch(config-ext-nacl)# deny tcp any any
Switch(config-ext-nacl)# permit icmp any any
Switch(config-ext-nacl)# deny udp any 171.69.0.0 0.0.255.255 lt 1024
Switch(config-ext-nacl)# deny ip any any log
Switch(config-ext-nacl)# exit
The Internet_filter ACL is applied to outgoing traffic and the marketing_group ACL is applied to
incoming traffic on a Layer 3 port.
Switch(config)# interface gigabitethernet3/0/2
Switch(config-if)# no switchport
Switch(config-if)# ip address 2.0.5.1 255.255.255.0
Switch(config-if)# ip access-group Internet_filter out
Switch(config-if)# ip access-group marketing_group in
Time Range Applied to an IP ACL
This example denies HTTP traffic on IP on Monday through Friday between the hours of 8:00 a.m. and
6:00 p.m (18:00). The example allows UDP traffic only on Saturday and Sunday from noon to 8:00 p.m.
(20:00).
Switch(config)# time-range no-http
Switch(config)# periodic weekdays 8:00 to 18:00
!
Switch(config)# time-range udp-yes
Switch(config)# periodic weekend 12:00 to 20:00
!
Switch(config)# ip access-list extended strict
Switch(config-ext-nacl)# deny tcp any any eq www time-range no-http
Switch(config-ext-nacl)# permit udp any any time-range udp-yes
!
OL-25303-03
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
Configuring IPv4 ACLs
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