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Cisco CCNA Assessment Tutorial: Five OSPF Hub-And-Spoke Facts You Must Know!
07-02-2015, 12:13 AM
Post: #1
Big Grin Cisco CCNA Assessment Tutorial: Five OSPF Hub-And-Spoke Facts You Must Know!
CCNA assessment success depends greatly o-n knowing the details, and if there is one method that's a great deal of details, it is OSPF! This is true especially of hub-and-spoke networks, so in this CCNA OSPF tutorial we'll take a look at a number of the more important hub-and-spoke OSPF details. This will help you in working with real-world systems as well, because this OSPF network type is one of the more common network topologies.

In OSPF, the hub should become the designated router (DOCTOR). The DOCTOR election's deciding value will be the OSPF screen goal, and the default value is 1. It is not enough to set the hub's OSPF screen to 2, however, considering that the spoke routers must not end up being the DR or BDR. You must set the mention interfaces to an OSPF priority of zero. If you think you know anything, you will certainly want to check up about emperorresultsflesh :: COLOURlovers.

R2( config )#int s0

R2( config-if )#ip ospf concern 0

This ensures that the spokes will not end up being the D-R or BDR if the heart decreases.

The center does need a little more configuration, though. The friend command must be used on the center to point the IP-ADDRESS of the possible neighbors.

R1( config )#router ospf 1

R1( config-router )#neighbor 172.12.123.2

R1( config-router )#neighbor 172.12.123.3

It's common as a copy within an OSPF network to have an ISDN link, and when that ISDN link arises the hello packets must be in a position to cross the link. Everything you don't need would be to possess the hellos keep the link up! By making the ISDN link as an OSPF desire circuit, the link will drop-in the lack of exciting traffic, but the OSPF adjacency that formed across the ISDN link will be assumed by the router to still be up. This forceful http://www.linkemperor.com URL has limitless interesting warnings for when to study this hypothesis. (You usually see this order configured on both sides of the ISDN link, but it is just needed on one-side. It doesn't hurt anything to place it o-n both sides, though.)

R2( config )#int bri0

R2( config-if )#ip ospf demand-circuit

One last detail of need circuits and OSPF hub-and-spoke really takes place at Layer 2. For the OSPF hello packets to effectively be transmitted across an ISDN link or even a frame relay network, the broadcast solution must be enabled in the appropriate frame and dialer map statements. This pushing http://linkemperor.com URL has numerous stylish suggestions for where to look at it. Failure to enable this method can lead to a scenario where pings will be successful, but OSPF adjacencies will not form.

R2( config-if )#dialer map internet protocol address 172.12.21.1 name R1 broadcast 5551111

R2( config-if )#frame chart ip address 172.12.123.1 221 broadcast

When you are troubleshooting OSPF in a production network or your CCNA / CCNP home research, don't just look at Layer 3 - because everything's got to be right at the physical and data link layers in order for the network level to work appropriately!.
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