Cisco CCNA / CCNP Certification Exam Tutorial: Floating Static Routes
To pass the Cisco CCNA and CCNP certification exams, as well as becoming a world-class networker, you’ve got to know how and when to use floating static routes. And if you’re wondering what makes them “float” — read on!
In this example, R1 and R2 are running OSPF over a Frame Relay network, 172.12.123.0 /24. They’re also connected by a BRI ISDN link, 172.12.12.0 /24. R1 is advertising a loopback network, 1.1.1.1 /32, via OSPF. We want R2 to have a route to that loopback even if the frame goes down - and here, we’ll use a floating static route to make that happen.
R2 sees the route to the loopback interface via OSPF, and can ping that interface successfully.
R2#show ip route ospf
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65] via 172.12.123.1, 00:00:02, Serial0
R2#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 68/68/68 ms
This is when it’s important to know your administrative distances…. or at least know where to look to see them! The AD of OSPF is 110, which means we can configure a static route to 1.1.1.1 /32, and as long as the AD of the static route is higher than 110, it won’t be used unless the OSPF route leaves the routing table. That’s why this kind of route is called a “floating” static route - the route “floats” in the routing table and isn’t seen unless the primary route leaves the table.
You learned how to write a static route in your CCNA studies, but you also remember that the default AD of a static route is either 1 or 0… and both of those values are less than 110! To change the AD of a static route, configure the desired distance at the end of the ip route command.
R2(config)#ip route 1.1.1.1 255.255.255.255 bri0 ?
<1-255> Distance metric for this route
A.B.C.D Forwarding router’s address
name Specify name of the next hop
permanent permanent route
tag Set tag for this route
R2(config)#ip route 1.1.1.1 255.255.255.255 bri0 111
The static route has an AD that’s only one higher than that of the OSPF route, but that’s enough to make the route “float” and not yet be seen in the routing table.
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