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17. Port security on access layer switchport

PDF version

Port security is feature that enable permit or deny traffic for end user PCs connected to access layer switch. Port security enable specify a group of valid MAC address on port. If maximum secure MAC address  is reached then security violation modes lead to protect, restrict or shutdown of port.

 

There are 3 ways how to configure port security:

1) Static secure MAC addresses - manually configured with

   switchport port-security mac-address MAC_ADDRESS

2) Dynamic secure MAC address - dynamic learned and stored only in address table (after restart cleared)

3) Sticky secure MAC address  - mac address are learned dynamically and saved in running config (next can be merged with startup config).

 

 

Default port security:

- disabled on port -> switchport port-security

- maximum nr. of secure MAC: 1

- violation mode: shutdown

- sticky address learning: disabled

 

Sample configs:

A) Dynamic port security configuration

s1#configure terminal

s1(C)# interface FastEthernet0 0/10

s1(c-if)#switchport mode access

s1(c-if)#switchport port-security

s1(c-if)#end

 

B) Sticky port security - can configure max. nr. of secure mac address, in this example we configure shutdown as the violation mode

 

s1#configure terminal

s1(C)# interface FastEthernet0 0/10

s1(c-if)#switchport mode access

s1(c-if)#switchport port-security     (enable port security)

s1(c-if)#switchport port-security maximum 20 (maximum nr. of secure address)

s1(c-if)#switchport port-security mac-address sticky    (enable sticky learning)

s1(c-if)#end

 

Table: Security violation modes

Violation

mode

Forward

traffic

Send syslog

message

Display error

message

Increase violation

counter

Shuts down

port

protect no no no no no
restrict no yes no yes no
shutdown no yes no yes yes

 

Verification commands:

  • show port-security  [interface interface-id]
  • show port-security  [interface interface-id] address

 

 

Our training scenario focused on port-security can be obtained from here (Packet tracer 5.2 or above you will need).

 

Network topology  consist of router acting on stick and switch. Port security is configured sticky for 10 mac address for port 20 to 24 with commands:

 

interface FastEthernet0/20
 switchport access vlan 30
 switchport port-security maximum 10
 switchport port-security mac-address sticky 
!
interface FastEthernet0/21
 switchport access vlan 30
 switchport port-security maximum 10
 switchport port-security mac-address sticky 
!
interface FastEthernet0/22
 switchport access vlan 30
 switchport port-security maximum 10
 switchport port-security mac-address sticky 
!
interface FastEthernet0/23
 switchport access vlan 30
 switchport port-security maximum 10
 switchport port-security mac-address sticky 
!
interface FastEthernet0/24
 switchport access vlan 30
 switchport port-security maximum 10
 switchport port-security mac-address sticky 
 
 
You are strongly encouraged to try 
1) Static port security for PC on vlan 10 on port fa0/10 with mac 0060.3EDC.1A80 - then disconnect device with mentioned mac and attach device with wrong mac (examine shuting down state of port), then correct port state and enable traffic forwarding.
 
 
2) Enable dynamic learning for PC on ports fa0/15 and fa0/16.

 

As example, output from show mac-address-table of switch

On port fa0/20 can be spot shared network segment (in our case it is hub interconnected segment).