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CCNA exam success depends greatly on understanding the details, and if theres one process thats lots of details, its OSPF! This is true specially of hub-and-spoke net-works, so in this CCNA OSPF tutorial well have a look at some of the more essential hub-and-spoke OSPF facts. To study more, you might choose to check out: Skaarup Riddle re.vu. This will allow you to in dealing with real-world systems as well, since this OSPF network type is among the more standard network topologies. In OSPF, the hub should become the designated router D-R. The DR elections choosing value is the OSPF program concern, and the default value is 1. Its not enough to set the hubs OSPF interface to 2, nevertheless, considering that the spoke routers must not become the DR or BDR. You must set the mention interfaces to an OSPF priority of zero. R2 config #int s0 R2 config-if #ip ospf goal 0 This ensures that the spokes will not become the D-R or BDR if the link falls. The heart does require a bit more configuration, though. The neighbor order can be used on the heart to indicate the INTERNET protocol 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 is common as a copy in an OSPF system to have an ISDN link, and the hello packets should be in a position to cross the link when that ISDN link pops up. Everything you dont want would be to have the hellos keep the link up! By configuring the ISDN link being an OSPF need enterprise, the link will drop-in the lack of interesting traffic, but the OSPF adjacency that produced across the ISDN link will be thought by the modem to still be up. You usually see this command designed on both sides of the ISDN link, but it is needed on one side. To compare additional info, please check out: http://www.linkemperor.com. It doesnt hurt anything to place it on both sides, though. R2 config #int bri0 R2 config-if #ip ospf demand-circuit A final aspect of OSPF hub-and-spoke and need circuits actually happens at Layer 2. For the OSPF hello packets to properly be transmitted across an ISDN link or even a frame relay network, the broadcast selection has to be allowed within the appropriate frame and dialer map statements. Failure allow this program can result in a situation where pings will become successful, but OSPF adjacencies will not form. To get one more viewpoint, consider looking at: http://linkemperor.com. R2 config-if #dialer guide internet protocol address 172.12.21.1 title R1 broadcast 5551111 R2 config-if #frame chart ip 172.12.123.1 221 broadcast If you are troubleshooting OSPF in a manufacturing network or your CCNA / CCNP home laboratory, do not only look at Layer 3 - because everythings got to be appropriate at the physical and data link layers for the network layer to operate effectively!. Discover additional info on a related encyclopedia - Click here: SodaHead.com - User 3984094.