How FDB Entries Get Added
The MAC entries that are added to the FDB are learned in the following ways:
- Source MAC entries are learned from ingress packets on all platforms. This is Layer 2 learning.
- On all switches, MAC entries can be learned at the hardware level.
- Virtual MAC addresses embedded in the payload of IP ARP packets can be learned when this feature is enabled.
- Static entries can be entered using the command line interface (CLI).
- Dynamic entries can be modified using the CLI.
- Static entries for switch interfaces are added by the system upon switch boot-up.
The ability to learn MAC addresses can be enabled or disabled on a port-by-port basis. You can also limit the number of addresses that can be learned, or you can lock down the current entries and prevent additional MAC address learning.
On SummitStacks with different ExtremeSwitching switch models, the FDB tables on some switches can be filled before the tables on other switches. In this situation, when a lower-capacity FDB table cannot accept FDB entries, a message appears that is similar to the following:
HAL.FDB.Warning> MSM-A: FDB for vlanID1 mac 00:00:03:05:15:04 was not added to slot 3 - table full.