The set-overload command of
IS-IS is used to configure the overload bit. In which scenarios is the wait for bgp configuration used?
On a BGP network, if a new device is added or an existing device is
restarted, because IS-IS routes are converged faster than BGP routes, the
device is used as the forwarding node. This causes traffic loss. If the set-overload command is run and the wait-for-bgp keyword is specified, the
device instructs other devices that it is in the overload state and does not
consider itself a forwarding node. The overload bit is deleted from LSP only
after BGP route convergence is complete, solving the traffic loss issue.
On the BGP network shown in this figure, if service traffic from router A to
router D is forwarded over router B and router C and router B is restarted due
to a fault, IS-IS routes are converged faster than BGP routes. Router A
discovers that the routes destined for router D are recursed to router B. In
this case, BGP routes of router B are not converged yet and has not learned
information about the routes destined for router D. This causes traffic loss.
With the set-overload command, the
overload bit of LSP is not deleted until BGP convergence is complete.