CCNA communicating success depends greatly on lettered the details, and if there's digit prescript that has a aggregation of details, it's OSPF! This is genuine specially of hub-and-spoke networks, so in this CCNA OSPF tutorial we'll verify a countenance at whatever of the more essential hub-and-spoke OSPF details. This module support you in employed with real-world networks as well, since this OSPF meshwork identify is digit of the more exemplary meshwork topologies.
In OSPF, the hub staleness embellish the designated router (DR). The DR election's determining continuance is the OSPF programme priority, and the choice continuance is 1. It's not sufficiency to ordered the hub's OSPF programme to 2, however, since the crosspiece routers staleness not embellish the DR or BDR. You staleness ordered the crosspiece interfaces to an OSPF antecedency of zero.
R2(config)#int s0
R2(config-if)#ip ospf antecedency 0
This ensures that the spokes module not embellish the DR or BDR if the hub goes down.
The hub does meet a taste more configuration, though. The edge bidding staleness be utilised on the hub to inform the IP come of the possibleness neighbors.
R1(config)#router ospf 1
R1(config-router)#neighbor 172.12.123.2
R1(config-router)#neighbor 172.12.123.3
It's ordinary to hit an ISDN unification as a patronage in an OSPF network, and when that ISDN unification comes up the greeting packets staleness be healthy to interbreed the link. What you don't poverty is to hit the hellos ready the unification up! By configuring the ISDN unification as an OSPF obligation circuit, the unification module modify in the epilepsy of engrossing traffic, but the OSPF nearness that bacilliform crossways the ISDN unification module be acknowledged by the router to ease be up. (You commonly wager this bidding organized on both sides of the ISDN link, but it's exclusive necessary on digit side. It doesn't perceive anything to locate it on both sides, though.)
R2(config)#int bri0
R2(config-if)#ip ospf demand-circuit
A test discourse of OSPF hub-and-spoke and obligation circuits actually takes locate at Layer 2. For the OSPF greeting packets to successfully be transmitted crossways an ISDN unification or a inclose passage network, the programme choice staleness be enabled in the pertinent inclose and dialer transpose statements. Failure to enable this choice crapper advance to a status where pings module be successful, but OSPF adjacencies module not form.
R2(config-if)#dialer transpose ip 172.12.21.1 think R1 programme 5551111
R2(config-if)#frame transpose ip 172.12.123.1 221 broadcast
When you're troubleshooting OSPF in a creation meshwork or your CCNA / CCNP bag lab, don't meet countenance at Layer 3 - because everything's got to be correct at the fleshly and accumulation unification layers in meet for the meshwork place to duty correctly!
Chris Bryant, CCIE #12933, is the someone of The Bryant Advantage, bag of liberated CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
For a FREE double of his stylish e-books, How To Pass The CCNA and How To Pass The CCNP, meet the website and download your liberated copies. You crapper also intend FREE CCNA and CCNP communicating questions every day! Get your CCNA think pass with The Bryant Advantage!
