network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
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Thursday, February 7, 2013

why ospf area's and other sundries...

these kinds of basic questions are tough on the spot...

why ospf areas? ospf areas are like, like life... yeah...

Areas limit the scope of route information distribution. It is not possible to do route update filtering within an area. The link-state database (LSDB) of routers within the same area must be synchronized and be exactly the same; however, route summarization and filtering is possible between different areas. The main benefit of creating areas is a reduction in the number of routes to propagate—by the filtering and the summarization of routes.

which really came in handy back when routers had shitty processors and 1k of ram...

An autonomous system boundary router (ASBR) advertises external destinations throughout the OSPF autonomous system. External routes are the routes redistributed into OSPF from any other protocol. In many cases, external link states make up a large percentage of the link states in the databases of every router. A stub area is an area in which you don't allow advertisements of external routes, thus reducing the size of the database even more. Instead, a default summary route ( is inserted into the stub area in order to reach these external routes. If you have no external routes in your network, then you have no need to define stub areas. 

no external routes equals no redistribution equals no stubs...

All areas in an OSPF autonomous system must be physically connected to the backbone area (area 0). In some cases where this physical connection is not possible, you can use a virtual link to connect to the backbone through a non-backbone area. As mentioned above, you can also use virtual links to connect two parts of a partitioned backbone through a non-backbone area. The area through which you configure the virtual link, known as a transit area, must have full routing information. The transit area cannot be a stub area.

good... and you use the area id virtual-link  command to accomplish this... then what ospf type is a virtual link... would someone please make up my mind...

doyle calls it a network type...

OSPF defines five network types:

Point-to-point networks
Broadcast networks
Nonbroadcast Multiaccess (NBMA) networks
Point-to-multipoint networks
Virtual links

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