Re: Filtering on by MAC. Mac address filtering does not work if the traffic is IP based. It only works for non-IP based traffic. If this helps.
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- Enabling Port Security
- How to block Mac address in cisco catal - Cisco Community
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Port security is a layer two traffic control feature on Cisco Catalyst switches. It enables an administrator configure individual switch ports to allow only a specified number of source MAC addresses ingressing the port. Its primary use is to deter the addition by users of "dumb" switches to illegally extend the reach of the network e. The addition of unmanaged devices complicates troubleshooting by administrators and is best avoided. Port security can be enabled with default parameters by issuing a single command on an interface:. Although only a single interface is used for illustration in this article, port security, if configured, is typically configured on all user-facing interfaces.
As you can see, there are a number of attributes which can be adjusted. We'll cover these in a moment. When a host connects to the switch port, the port learns the host's MAC address as the first frame is received:.
Now, we disconnect the host from the port, connect a small switch or hub, and reconnect the original host plus a second, unauthorized host so that they both attempt to share the access port. Observe what happens as soon as the second host attempts to send traffic:.
Inspecting the status of port security on the port again, we can see that the new MAC address triggered a violation:. By default, a port security violation forces the interface into the error-disabled state. An administrator must re-enable the port manually by issuing the shutdown interface command followed by no shutdown.
Enabling Port Security
This must be done after the offending host has been removed, or the violation will be triggered again as soon as the second host sends another frame. By changing the violation mode to restrict , we are still alerted when a violation occurs, but legitimate traffic remains unaffected:. Unfortunately, violating traffic will continue to trigger log notifications, and the violation counter will continue to increase, until the violating host is dealt with.
By default, port security limits the ingress MAC address count to one. This can be modified, for example, to accommodate both a host and an IP phone connected in series on a switch port:. An administrator has the option of statically configuring allowed MAC addresses per interface. Obviously, this is not a scalable practice. A much more convenient alternative is to enable "sticky" MAC address learning; MAC addresses will be dynamically learned until the maximum limit for the interface is reached.
After a MAC address has been learned, it is recorded to the configuration similarly to as if it were entered manually:. By default, secure MAC addresses are learned in effect permanently. Aging can be configured so that the addresses expire after a certain amount of time has passed. This allows a new host to take the place of one which has been removed.
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Aging can be configured to take effect at regular intervals, or only during periods of inactivity. The following example configures expiration of MAC addresses after five minutes of inactivity:. At this point, the old address will be re-learned the next time a frame is sent from that host, or a new host can take its place. To avoid having to manually intervene every time a port-security violation forces an interface into the error-disabled state, one can enable auto-recovery for port security violations.
A recovery interval is configured in seconds. Ten minutes after a port was error-disabled, we can see that the port is automatically transitioned back into operation:.
How to block Mac address in cisco catal - Cisco Community
This is a great way to automatically clear port security violations after the user has been given an opportunity to remove the offending host s. Note that is the cause is not cleared, the violation will trigger again after the port comes back up, re-initating the auto-recovery cycle. Although a deterrent, port security is not a reliable security feature, as MAC addresses are trivially spoofed, and multiple hosts can still easily be hidden behind a small router.
IEEE Posted in Security , Switching. I actually had to learn his the other day.
We had enabled all user facing ports on our G's using the Catalyst Web Interface, configuring them as "Desktop" ports. As a result, when a rogue switch is connected, the port was shutdown permanently and a manual "shut" and "no shut" would be needed each time an offense occurred. Only glanced over the article, but port-security is definitely a cool feature to have in smaller to medium sized enviroments, good for preventing mac-address-table flooding attacks where a user may attempt to take advantage of a full mac table and sniffing those unknown unicast frames that will get flooded once the switch can no longer learn additional mac addresses.
Talk about just in time.
I was needing to implement some of these features this week. Thanks for the write up. Something to keep in mind: some protocols, e. The switch port where the routers are connected will see two separate mac address from that port. If the port is set to MAX 1 then the port will err-disable. There's an issue with VoIP phones or any other swich and port security that's caused us some interesting problems in the past. A user would connect to their device to a port behind a VoIP phone.
At this point the switch would learn their devices MAC address and tie it to the port. If that device is then unplugged and moved to a different port on the same switch, the switch will not properly pass traffic to the new port. How to block Mac address in cisco catalyst switches ,, Just enter this command As per your network Labels: Network Management.
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Cisco Networking: Static ARP Entry Managment
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