On the existing network, the traffic needs to be adjusted in the entire network at the time of cutover and upgrade to prevent the traffic from passing the router being upgraded. However, in many cases, there are many links; the work is heavy if the traffic is adjusted one by one. How to prevent the traffic from passing the RT being upgraded?
The overload bit in ISIS, that is, the set-overload command can directly implement this function.
There is a similar function in OSPF, that is, OSPF Stub Router Advertisement, which can be implemented in RFC3137 by a router generating and advertising a router LSA with the maximum metric (LSInfinity: 0xFFFF) to stub links. In this manner, the LSA with the maximum metric causes a router to select other routers instead of newly added routers at the time of routing and newly added routers do not become transit routers to other networks, with traffic migration naturally implemented.
This Upgrade can leave out much of traffic adjustment, with the link rapidly adjusted.
This command is very simple and router-LSA will be automatically cleared because of timeout at the time of restarting during the upgrade, without causing network flapping. After the upgrade, undoing corresponding commands can rapidly present the process of traffic switchover for observation. Field engineers are strongly recommended to use this command in their work.