Summarizing routes is a vital skill to learn to pass the BSCI exam and get one step closer to earning your CCNP. The actual binary conversions are only part of the test, though! You've got to know how to correctly apply the summary routes, and that differs from one protocol to the next. In the last few CCNP / BSCI tutorials, we've looked at using the "area range" and "summary-address" commands to perform OSPF route summarization. Today, we'll take a look at summarizing routes in EIGRP.
Laptop Battery We'll use the following four loopback addresses in this example:
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.
Thinkpad Loopback 16, 16.16.16.16 /32
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Microsoft Loopback 17, 17.17.17.17 /32
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Laptop Computers Loopback 18, 18.18.18.18 /32
Configuring EIGRP stub routers also combats the SIA problem. EIGRP stub routers are not queried for routes when the hub does not have a feasible successor for a successor route that has gone down. By default, directly connected networks and summary routes. To change this default, use the eigrp stub command followed by the types of routes you want the stub to advertise back to the hub. (The eigrp stub command run by itself configures the router as stub.)
Laptop Computer Loopback 19. 19.19.19.19 /32
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Desktop Computer On R1, we'll place these four addresses into EIGRP AS 100.
Notebooks R1(config-if)#router eigrp 100
Lenovo R1(config-router)#network 16.16.16.16 0.0.0.0
Hard Drive R1(config-router)#network 17.17.17.17 0.0.0.0
Travelstar R1(config-router)#network 18.18.18.18 0.0.0.0
Gateway R1(config-router)#network 19.19.19.19 0.0.0.0
Laptop Parts R3 is an EIGRP neighbor of R1, and that router's EIGRP routing table now looks like this:
Software R3#show ip route eigrp
Hard Drives 17.0.0.0/32 is subnetted, 1 subnets
Electronics D 17.17.17.17 [90/2297856] via 172.12.123.1, 00:00:29, Serial0
Canon 16.0.0.0/32 is subnetted, 1 subnets
Desktop Pc D 16.16.16.16 [90/2297856] via 172.12.123.1, 00:00:36, Serial0
Desktop Computers 19.0.0.0/32 is subnetted, 1 subnets
Think Pad D 19.19.19.19 [90/2297856] via 172.12.123.1, 00:00:08, Serial0
Repair 18.0.0.0/32 is subnetted, 1 subnets
Data Recovery D 18.18.18.18 [90/2297856] via 172.12.123.1, 00:00:22, Serial0
Cisco
To perform manual route summarization, write out the network addresses in binary and then determine the point at which the addresses no longer have a bit in common. For these four addresses, it will be enough to write out the first octet in binary:
Keyboard 16 00010000
Monitor 17 00010001
Desktop 18 00010010
Infosys 19 00010011
Refurbished Laptops
Working from left to right, the common bits are the first six bits - 000100xx. In decimal, this value is 16. The summary mask must be determined as well, and that value is derived from putting a "1" in the mask for each common bit. With the first six bits all set to one - 11111100 - the resulting mask is 252.0.0.0. The full summary address is 16.0.0.0 252.0.0.0.
Wipro In EIGRP, the summary address is actually configured on an interface, not under the routing process.
Lap Top R1(config)#interface serial0
Refurbished R1(config-if)#ip summary-address eigrp 100 16.0.0.0 252.0.0.0
Memory
02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is down: summary configured
Intel 02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is down: summary configured
As400 02:40:16: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is up : new adjacency
Averatec
02:40:17: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is up: new adjacency
Hardware There's an immediate side effect here that most books leave out. Your EIGRP adjacencies are going to come down after you configure this summary, but they should come back up quickly. The key word there is "should". If you configure EIGRP summary addresses on a production network, you may want to do this during non-peak hours. The timestamps on the above commands indicate that the adjacencies were down for about 27 seconds over the NBMA network. That's about 30 minutes in end-user time. ;)
Dual Xeon Check R3's EIGRP routing table.
Storage R3#show ip route eigrp
Seagate D 16.0.0.0/6 [90/2297856] via 172.12.123.1, 00:01:46, Serial0
Computer Sales The four summarized routes are no longer in the routing table, and they have been replaced by the summary route shown at the bottom of the routing table. Notice the mask is /6, which is prefix notation for 248.0.0.0.
Computer Hardware Knowing how and why to summarize routes is a valuable skill, regardless of the protocol in use. But before you take the BSCI exam on your way to the CCNP, make sure you know how to perform summarization with all of the core protocols!
Printers
Technology 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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