Passing the BSCI exam and earning your CCNP certification
demands that you add greatly to the networking skills foundation
you created when you studied for your CCNA certification.
You learned quite a bit about static routing and default static
routing when you passed the CCNA test, and it does seem like
that should be all you need to know about static routing,
right?
One thing you'll learn as you continue to earn Cisco certifications
is that there's always something else to learn! You may have
heard the term "floating static route", which does
suggest some interesting mental pictures. "Floating"?
Floating on what?
In a way, a floating static route is "floating"
in your routing table. A floating static route is a route
that will be used only if routes for the same destination
but with a lower administrative distance are removed from
the table. For example, you could be using an OSPF-discovered
route as your primary route to a given destination, and the
floating static route would serve as a backup route that would
be used only if the OSPF route leaves the routing table.
Now, how can that happen? After all, OSPF has an administrative
distance of 110 and static routes have ADs of one or zero,
depending on whether it's configured with a next-hop IP address
or a local exit interface. One way or the other, 1 and 0 are
still less than 110!
When you want to configure a floating static route, you must
assign the route an AD higher than that of the primary route.
In this case, we've got to create a static route with an AD
higher than 110. We do this by using the "distance"
option at the end of the "ip route" command.
R1(config)#ip route 110.1.1.0 255.255.255.0 172.12.123.1
?
<1-255> Distance metric for this route
name Specify name of the next hop
permanent permanent route
tag Set tag for this route
R1(config)#ip route 110.1.1.0 255.255.255.0 172.12.123.1 111
The number entered at the very end of the "ip route"
command is the AD of that route. If there is an OSPF route
for 110.1.1.0 /24, that will be the primary route, and the
floating static route will not be used unless the OSPF route
is taken out of the routing table.
Floating static routes aren't just a good thing to know for
the BSCI exam and your CCNP certification pursuit - they're
very practical in the real world as well.
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!
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