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Configuring Network Security with ACLs
Configuration Examples for Network Security with ACLs
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 GigabitEthernet1/17
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
Applying Time Range to an IP ACL: Example
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
!
Switch(config-ext-nacl)# exit
Switch(config)# interface GigabitEthernet1/17
Switch(config-if)# ip access-group strict in
Creating Commented IP ACL Entries: Examples
In this example of a numbered ACL, the workstation that belongs to Jones is allowed access, and the workstation that
belongs to Smith is not allowed access:
Switch(config)# access-list 1 remark Permit only Jones workstation through
Switch(config)# access-list 1 permit 171.69.2.88
Switch(config)# access-list 1 remark Do not allow Smith workstation through
Switch(config)# access-list 1 deny 171.69.3.13
In this example of a numbered ACL, the Winter and Smith workstations are not allowed to browse the web:
Switch(config)# access-list 100 remark Do not allow Winter to browse the web
Switch(config)# access-list 100 deny host 171.69.3.85 any eq www
Switch(config)# access-list 100 remark Do not allow Smith to browse the web
Switch(config)# access-list 100 deny host 171.69.3.13 any eq www
In this example of a named ACL, the Jones subnet is not allowed access:
Switch(config)# ip access-list standard prevention