Making The Most Of Cisco's CCNP Program Changes
As you probably know by now, Cisco's making some sweeping changes in their Cisco Certified Network Professional (CCNP) program.
Why NAT Traversal Matters To You!
Have you ever wanted to connect to your home machine from work -- or vice versa -- but were unable to do so because you were behind a Linksys, NetGear, or Apple router?
Official Cisco CCIE Boot Camps
Regarded as the highest level of Cisco certification on the hierarchy of Cisco networking solutions and implementing professional training, CCIE (Cisco Certified Internetwork Expert) certifications are highly...
Configuring CGMP On Routers & Switches
If a Layer Two switch doesn't have the capabilities to run IGMP Snooping, it will be able to run CGMP - Cisco Group Membership Protocol. CGMP allows the multicast...
Google And The Need For Speed
If the scientists who claim news content has a half-life
of 36 hours online before it falls off the radar of Internet
users are correct, Google's successor online might match
EIGRP Stuck-In-Active Routes
Passing the BSCI exam and earning your CCNP is all about knowing the details, and when it comes to EIGRP SIA routes, there are plenty of details to know.
Frame Relay DLCIs And Mappings
Passing the CCNA is tough, and one of the toughest parts is keeping all the acronyms straight! Frame Relay has plenty of those, and today weīre going to examine what DLCIs do and how theyīre mapped on a Cisco router.
OSPF Hub-And-Spoke Details You Must Know!
By Chris Bryant
CCNA exam success depends greatly on knowing the details, and if thereīs one protocol that has a lot of details, itīs OSPF!
This is true particularly of hub-and-spoke networks, so in this CCNA OSPF tutorial weīll take a look at some of the more important hub-and-spoke OSPF details. This will help you in working with real-world networks as well, since this OSPF network type is one of the more typical network topologies.
In OSPF, the hub must become the designated router (DR). The DR electionīs deciding value is the OSPF interface priority, and the default value is 1. Itīs not enough to set the hubīs OSPF interface to 2, however, since the spoke routers must not become the DR or BDR. You must set the spoke interfaces to an OSPF priority of zero.
R2(config-if)#ip ospf priority 0
This ensures that the spokes will not become the DR or BDR if the hub goes down.
The hub does require a bit more configuration, though. The neighbor command must be used on the hub to indicate the IP address of the potential neighbors.
R1(config)#router ospf 1
Itīs common to have an ISDN link as a backup in an OSPF network, and when that ISDN link comes up the hello packets must be able to cross the link. What you donīt want is to have the hellos keep the link up! By configuring the ISDN link as an OSPF demand circuit, the link will drop in the absence 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 configured on both sides of the ISDN link, but itīs only needed on one side. It doesnīt hurt anything to put it on both sides, though.)
R2(config-if)#ip ospf demand-circuit
A final detail of OSPF hub-and-spoke and demand circuits actually takes place at Layer 2. For the OSPF hello packets to successfully be transmitted across an ISDN link or a frame relay network, the broadcast option must be enabled in the appropriate frame and dialer map statements. Failure to enable this option can lead to a situation where pings will be successful, but OSPF adjacencies will not form.
R2(config-if)#dialer map ip 126.96.36.199 name R1 broadcast 5551111
R2(config-if)#frame map ip 188.8.131.52 221 broadcast
When you\īre troubleshooting OSPF in a production network or your CCNA / CCNP home lab, don\īt just look at Layer 3 - because everything\īs got to be right at the physical and data link layers in order for the network layer to function correctly!
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of CCNA and CCNP tutorials and daily exam questions, as well as The Ultimate CCNA and CCNP Study Packages.