These computers will have a MAC address, it comes with their network cards.
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- Clearing Dynamic Addresses from the MAC Table;
- Table of Contents!
- Configuring Cisco Switch MAC Address and Security Settings!
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No Questions Asked! When the aging time for a MAC address in the table expires, the address is removed. It places these addresses into its Ethernet switching table, along with two other pieces of information—the interface on which the traffic was received and the time when the address was learned.
When the switch receives traffic on an interface, it searches the Ethernet switching table for the MAC address of the destination. Flooding allows the switch to learn about destinations that are not yet in its Ethernet switching table. If a particular destination MAC address is not in the Ethernet switching table, the switch floods the traffic to all interfaces except the interface on which it was received. When the destination node receives the flooded traffic, it sends an acknowledgment packet back to the switch, allowing the switch to learn the MAC address of the node and to add the address to its Ethernet switching table.
The switch uses a mechanism called aging to keep the Ethernet switching table current. For each MAC address in the Ethernet switching table, the switch records a timestamp of when the information about the network node was learned. Each time the switch detects traffic from a MAC address that is in its Ethernet switching table, it updates the timestamp of that MAC address.
A timer on the switch periodically checks the timestamp, and if the MAC address of a node is older than the value set, the switch removes that MAC address from the Ethernet switching table. However, your question sounds like a poor solution to any problem. What are you really trying to accomplish?
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I have a very long list of mac addresses of different servers on the network and I need to match them against CAM tables of all switches in order to find out to which defices it's connected directly I already know how to get CAM table of mac addresses that are directly connected. That is what I though, however currently we scan at night and reading CAM tables from almost every switch, we get around a third or half of all the devices. That's possibly because we ran at night and different servers have activity during different times of day.
Understanding MAC Table Aging
Run the script during the day. We've got several thousands of hosts, and the sweep takes around half an hour.
Have you looked at nMap? The ping sweep in nMap is very fast.
You are right. If somehow I can run it faster, it might even work for me. To enable mac address-notification mac address-table notification change history-size mac address-table notification change Furthermore, you can have it send SNMP traps so you can collect all the reports easily from an SNMP daemon. Jason Seemann Jason Seemann 1, 6 6 silver badges 9 9 bronze badges. I didn't know about this feature, thanks!
It would be useful in case we had few devices, however we've got over , so pushing this change on all them isn't that viable. Guardian Guardian 4 4 bronze badges.
- mac-address-table aging-time — global - Cisco IOS in a Nutshell, 2nd Edition [Book].
- Configuring a Static MAC Address.
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- Verifying the Configuration!