If there's one CCNP / BSCI topic that looks so easy but can lead to a real headache, it's route redistribution. I'm not even talking about the routing loops and suboptimal routing that can result when route redistribution is done without proper planning - I'm talking about the basic commands themselves. Leaving out one single command option, or forgetting what else needs to be redistributed when redistributing dynamically discovered routes, can leave you with a routing table that looks complete but does not result in full IP connectivity.
Laptop Battery In this free CCNP / BSCI tutorial series, we'll take a look at three common errors in route redistribution configurations, and how to fix them. We'll use three routers, R1, R3, and R5. R1 and R5 are in a RIPv2 domain and R1 and R3 are in an OSPF domain. R1 will be performing two-way route redistribution.
Occasionally, during your CCNA and CCNP studies, you'll run into a term that just doesn't quite make sense to you. (Okay, more than occasionally!) One such term is "reverse telnet". As a Cisco certification candidate, you know that telnet is simply a protocol that allows you to remotely connect to a networking device such as a router or switch. But what is "reverse telnet", CCNP home lab setup
Thinkpad R5 is advertising its loopback, 5.5.5.5/24, into the RIPv2 domain. R1 sees this route in its RIP routing table:
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Microsoft R1#show ip route rip
Passing the BCSI exam and earning your CCNP certification requires you to know OSPF stub areas inside and out. Stub areas, total stub areas, stub stub areas ... and pretty soon your head is swimming. Then when you hear that EIGRP offers stub routing, your first reaction may be unprintable! But while EIGRP stub routing is effective in the right situation, it's not as complex as OSPF stub routing. Let's take a look at basic EIGRP stub routing.
Laptop Computers 5.0.0.0/24 is subnetted, 1 subnets
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Laptop Computer R 5.5.5.0 [120/1] via 100.1.1.5, 00:00:01, Ethernet0
Then there are the hidden partitions. On computers that are shipped with the operating system installed, manufacturers have already installed one or two partitions containing a complete system image, boot information, and even parts of the Windows operating system. They do this in part because it makes computer troubleshooting easier and in part because it keeps you from using your recovery CD to copy Windows onto other computers in violation of your licensing agreement.
Desktop Computer For R3 to see this route, route redistribution must be configured on R1. We'll use the redistribute rip command to do so.
Notebooks R1(config)#router ospf 1
Lenovo R1(config-router)#redistribute rip
Hard Drive % Only classful networks will be redistributed
Travelstar The router immediately gives us a message that "only classful networks will be redistributed". What does this mean? Let's go to R3 and see if that router is receiving this route.
Gateway R3#show ip route ospf
Laptop Parts < no output >
Software When we get no result from a show command, that means there's nothing to show. The only routes that will be successfully redistributed with the current configuration on R1 are classful networks, and 5.5.5.0/24 is a subnet.
Hard Drives To further illustrate the point, a classful network has been added to R5. This network is 16.0.0.0 /8, and is now being advertised by RIP. R1 sees this network as classful...
Electronics R1#show ip route rip
Canon R 16.0.0.0/8 [120/1] via 100.1.1.5, 00:00:00, Ethernet0
Desktop Pc 5.0.0.0/24 is subnetted, 1 subnets
Desktop Computers R 5.5.5.0 [120/1] via 100.1.1.5, 00:00:00, Ethernet0
Think Pad ... and R3 is receiving the route through redistribution.
Repair R3#show ip route ospf
Data Recovery O E2 16.0.0.0/8 [110/20] via 172.12.123.1, 00:00:08, Serial0.31
Cisco To redistribute both classful and classless networks, the option "subnets" must be added to the redistribute command on R1.
Keyboard R1(config)#router ospf 1
Monitor R1(config-router)#no redistribute rip
Desktop R1(config-router)#redistribute rip subnets
Infosys R3 will now see both the classful and classless networks being redistributed into OSPF. (100.1.1.0 is the network connecting R1 and R5.)
Refurbished Laptops R3#show ip route ospf
Wipro O E2 16.0.0.0/8 [110/20] via 172.12.123.1, 00:00:20, Serial0.31
Lap Top 100.0.0.0/24 is subnetted, 1 subnets
Refurbished O E2 100.1.1.0 [110/20] via 172.12.123.1, 00:00:20, Serial0.31
Memory 5.0.0.0/24 is subnetted, 1 subnets
Intel O E2 5.5.5.0 [110/20] via 172.12.123.1, 00:00:20, Serial0.31
As400 This is one of the most common errors made during route redistribution, but now you know what to look out for! In the next part of this free CCNP / BSCI tutorial, we'll take a look at another such error.
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Hardware Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (http://www.thebryantadvantage.com), home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, Ultimate CCNP Study Packages, and CCNA CBT video training. Pass the CCNA exam ,BSCI exam , and BCMSN exam with Chris Bryant, CCIE #12933!
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