black holes

[primavat]

routers using auto summary with classless protocols (ie eigrp) don't generate a black hole, even when they have discontiguous IP networks. Instead, they summarize the two discontiguous networks, advertise a much larger route to the rest of the network, but retain the smaller, more granular routes of the discontiguous networks. Am I right so far?

When do black holes actually occur? When using RIP?

[samuel_yip]

Black holes usually appeared when routes are not sychnorize in iBGP. For example. three routers in a network. Router A peer eBGP with ISP A and Router B peer eBGP with ISP B. Router C is a transit router that interconnect both Router A and Router B. There is no direct connection from Router A to Router B. The IGP in Router A, B and C is OSPF. When Router A learns a prefer route via BGP that is to be send via Router B, the packet will be forwarded to Router C. Router C without running BGP does not contain the routes and hence drop. This is a typically of black hole in BGP.

Hope I expressed myself correct.