@wrathfulcolleag
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CCNA assessment success depends greatly o-n understanding the details, and if there's one process that has a great deal of details, it's OSPF! This is true particularly of hub-and-spoke net-works, therefore in this CCNA OSPF guide we'll take a look at several of the more impor-tant hub-and-spoke OSPF details. This can help you in dealing with real-world systems as well, because this OSPF network type is among the more common network topologies. In OSPF, the heart must become the designated router (DOCTOR). The DR election's selecting value could be the OSPF software goal, and the default value is 1. It is not enough to create the hub's OSPF interface to 2, nevertheless, because the spoke routers mustn't get to be the DR or BDR. You need to set the interfaces to an OSPF priority of zero. R2( config )#int s0 R2( config-if )#ip ospf priority 0 This ensures that the spokes won't become the DR or BDR if the link falls. The hub does need a extra configuration, though. The neighbor command is employed on the center to indicate the IP-ADDRESS of the potential 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 backup in a OSPF system to have an ISDN link, and when that ISDN link comes up the hello packets must be able to cross the link. To get further information, please consider looking at: partner sites. What you do not want is to have the hellos keep the link up! By establishing the ISDN link being an OSPF demand enterprise, the link will drop in the lack of interesting traffic, but the OSPF adjacency that formed across the ISDN link will be assumed by the router to still be up. (You usually see this command designed on both sides of the ISDN link, however it is just required on one side. It does not hurt anything to place it o-n both sides, though.) R2( config )#int bri0 R2( config-if )#ip ospf demand-circuit One last aspect of OSPF hub-and-spoke and demand tracks really takes place at Layer 2. Visit open in a new browser to check up why to mull over it. If you are concerned by shopping, you will possibly desire to explore about in english. For the OSPF hello packets to effectively be transmitted across an ISDN link or a frame relay network, the broadcast alternative should be allowed in the correct frame and dialer map statements. Failure make it possible for this method can cause a scenario where pings will achieve success, but OSPF adjacencies will not form. R2( config-if )#dialer place internet protocol address 172.12.21.1 title R1 broadcast 5551111 R2( config-if )#frame place internet protocol address 172.12.123.1 221 broadcast When you are troubleshooting OSPF in a production network or your CCNA / CCNP house lab, do not only look at Layer 3 - since everything's got to be right at the physical and data link layers for the network layer to function appropriately!.
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