(((1- The default-information originate OSPF routing process subcommand will generate a default route into the OSPF domain.
2- By default this default cannot be advertised unless the local device actually has a default route installed
in the routing table.
3- This stipulation is added to prevent the case where default reachability is lost from an upstream peer, but default reachability is still advertised into the OSPF domain.
4- An example of this case is as follows.
Suppose that your OSPF domain has two or more connections to an upstream Internet provider. At these exit points from your internal network the border routers are learning a default from the ISP.
5- Additionally these border routers are generating default routes into the OSPF domain by issuing the default-information originate routing process subcommand.
6- Now suppose that one of these connections to the upstream provider is lost. If the border router with the lost upstream connection is still advertising default reachability into the OSPF domain some of the traffic will be blackholed.
7- Instead the router with the
lost connection should withdraw the default route from the OSPF domain, which
in turn would cause all internal devices to reroute out a still valid exit point from the network))).
Regarding to point 6 how does it make a blackhole ?
Re: The default-information originate and blackhole
Because the router still anounces default route into ospf domain, and the packets which prefer this route will be blackholed. because the link to isp is broken. and the router will drop these packets.but the packets those prefer the other default route will go through the second router cause its link to isp is still up.
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