What does the Stale status code mean in the BGP table?

The Stale status code in the BGP table indicates that the entry must be refreshed when the remote BGP neighbor returns. This typically occurs when the Next Hop attribute for that route is no longer reachable, but the information about the route is still retained in the BGP table. Essentially, it signifies that the destination is potentially still valid, but the routing information needs to be validated again to ensure it is current and reachable.

In practice, this status helps maintain route information during transient network issues without immediately discarding the route. It allows BGP to quickly reestablish connectivity without having to relearn the route from scratch, thus speeding up the convergence process when the original BGP neighbor becomes reachable again. This mechanism is critical for maintaining stability and performance in large-scale networks where intermittent connectivity can occur.

The other statuses indicate different situations. For example, an entry marked as invalidated would suggest that it cannot be used at all, while flapping would indicate instability of routes. This distinction highlights the importance of the Stale status in the context of BGP’s routing strategies.