You can configure a reachable lifetime for a static entry. The stale and down lifetime timer is fixed by the system as infinite (For an entry in the STALE or DOWN state, the output of the show device-tracking database command displays the Time Left column as “N/A”). This means that when a static entry enters the STALE or DOWN state it remains in this state, and in the binding table, indefinitely. A static entry can be removed from the binding table only by the actions listed below. It cannot be deleted from the binding table by using clear commands or by any other event: • You remove the entry by configuring the no form of the above command. • A local entry replaces the static entry.
A local entry is an entry that is automatically created by the system when you configure an SVI on the device. When configuring the SVI, if you use the same IP address as the static entry then the static entry is replaced with the local entry, because the local entry has a higher priority. This replacement of a static entry by a local entry is introduced only in Cisco IOS XE Bengaluru 17.4.1 onwards; it does not happen in earlier releases. In the output of the show device-tracking database details privileged EXEC command, local entries are prefixed with the letter "L". For more information about static binding entries, see the device-tracking binding command in the command reference.
Note In addition to the primary or key events listed above, there is a specific scenario in which a ping can result in a device-tracking entry. If a sender’s ARP cache or IPv6 neighbor table doesn’t have the target’s IP address yet, then a ping triggers an ARP packet for IPv4, or ND packet for IPv6. This can result in a device-tracking entry. But if the target IP is already in the ARP cache or IPv6 neighbour table, no ARP or ND packet is generated when you ping - in which case SISF cannot learn the IP address. Device-Tracking SISF-based device-tracking is disabled by default. You can enable the feature on an interface or VLAN.
When you enable the feature, the binding table is created, followed by subsequent maintenance of the binding table. The events listed in the Binding Table Sources, on page 5 section act as triggers for SISF-based device-tracking, to track the presence, location, and movement of hosts in the network, to populate and maintain the binding table. For example, if information about a host is learnt by means of an ARP or ND packet, every subsequent ARP or ND packet from the same host acts as an alert for SISF-based device-tracking, to refresh the entry in the binding table, thus indicating if the host is still present in the same location or has moved.
The continuous process of snooping of packets that the switch receives, extraction of device identity (MAC and IP address), and storage of information in the binding table of the switch, ensures binding integrity and maintains the reachability status of the hosts in the binding table. For information how to enable SISF-based device-tracking, see How to Configure SISF, on page 20 . Configuring Switch Integrated Security Features Device-Tracking Configuring Switch Integrated Security Features 7