PC can't work on another port when port security is enabled

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Nov 14th, 2009
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For the infrastructure security purpose, I configured port security feature on the port and DHCP snooping on the switch. After that I found the problem that when the PC plugged into the port first, it can obtain the ip address through DHCP, but if the PC moved to another port in the same VLAN on the same switch, it can't obtain the ip address any more while other PCs plugged into the same port worked correctly.

what would be the reason to prevent the PC from obtaining the ip address. Port security feature or DHCP snooping?



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Overall Rating: 3 (2 ratings)
mmacdonald70 Sat, 11/14/2009 - 08:31
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Port security. When the switch learns an address on one port, it is considered a violation to see it on another port. Clear the mac address from the first port.

qilin zhang Sat, 11/14/2009 - 19:39
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Hi Mmacdonald,

Does that mean Port Security feature is not suitable for the LAN which has a lot of laptops and need change their location frequently.



Muhammad Anser Khan Sun, 11/15/2009 - 04:53
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No. You can set the aging time for releasing MAC address from the port.

for example:

Following command will do When there is no traffic for 1 mins under the interface. It will release the MAC address from this port:

Switch(config-if)#switchport port-security aging time 1

Switch(config-if)#switchport port-security aging type inactivity




tharsan86 Sat, 11/14/2009 - 10:23
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Hi Kirin

Cisco Port-Security can help to

•restrict the MAC-address or addresses that can connect through a switchport [default: first connected device MAC Address]

•restrict the number of MAC-Addresses that can connect through a switchport [default is 1 and maximum is 128]

•set aging in minutes of the MAC Addresses registed

•Action to take when there is a violation detected (default is to disable the port and send an SNMP Trap message to the SNMP management server (if any))

To display the security MAC-Address table

Switch# show port-security address- lists all the learned MAC addresses by interface

Show port-security interface fa0/1 - shows the detailed port security settings for an interface, including enable/disable status

To clear the violation on the port

Issue the following command:

Switch#clear port-security interface sticky fa0/0(choose the down int )

and then issue commands "shut" and "no shut" on the interface that has been put in down/down state due to port-security violation.

***pls rate if it helps***




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