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Cisco CCNA Certification Exam Tutorial: OSPF Hub-And-Spoke |
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CCNA certification demands that you master the basics of
OSPF, and for many studying for the CCNA exam, their first
exposure to OSPF is a hub-and-spoke configuration. That's
a tough way to get started, because a hub-and-spoke configuration
built over an NBMA technology such as Frame Relay requires
quite a bit of attention to detail. Let's take a quick look
at several common OSPF configuration errors and how to avoid
them on your CCNA test.
Make sure the hub is the designated router and that there
are no backup designated routers. This is done by setting
the OSPF interface priority to zero on the spoke routers.
This not only ensures that the hub wins the DR election with
its default OSPF interface priority of 1, but it prevents
the spokes from ever having a chance to become the DR or BDR.
Configure neighbor statements on the hub. Since we're dealing
with an NBMA network, the hub cannot dynamically discover
its neighbors. Neighbor statements are not needed on the spokes.
(They don't hurt anything, but they don't do anything, either.)
Finally, if your OSPF adjacencies do not form as expected,
make sure to use your OSI model knowledge to approach the
problem. The issue may actually be at Layer Two, with your
Frame Relay configuration. If you don't use the "broadcast"
option on your frame relay statements, OSPF hellos will not
be transmitted successfully between potential neighbors. OSPF
hellos are multicast, but the "broadcast" option
for Frame Relay includes multicasts.
By paying special attention to these details, you're that
much close to CCNA exam day success and earning your certification.
I recommend that you get some experience with configuring
OSPF hub-and-spoke before taking the CCNA exam, because it’s
by actually performing tasks such as this that makes you supremely
confident on CCNA test day.
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage,
home of free CCNP and CCNA tutorials, The Ultimate CCNA Study
Package, and Ultimate CCNP Study Packages. For a FREE copy
of his latest e-books, “How To Pass The CCNA” and
“How To Pass The CCNP”, just visit the website!
You can also get FREE CCNA and CCNP exam questions every day!
Pass the CCNP exam with The Bryant Advantage!
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