A quick check in a search engine for “troubleshoot SIA” will bring up quite a few matches. Troubleshooting SIA routes is very challengin in that theres no one reason they occur.

View the EIGRP topology table with the show ip eigrp topology command, and youll see a code next to every successor and feasible successor. A popular misconception is that we want these routes to have an “A” next to them – so theyre active. Thats what we want, right? Active routes sound good, right?

Well, they sound good, but theyre not. If a route shows as Active in the EIGRP topology table, that means that DUAL is currently calculating that route, and its currently unusable. When a route is Passive (“P), that means its not being recalculated and its a usable route.

Generally, a route shown as Active is going to be there for a very short period of time by the time you repeat the command, hopefully that Active route has gone Passive. Sometimes that doesnt happen, though, and the route becomes SIA – Stuck In Active.

A route becomes SIA when a query goes unanswered for so long that the neighbor relationship is reset. From experience, I can tell you that troubleshooting SIA routes is more of an art form than a science, but there are four main reasons a route becomes SIA:

The link is unidirectional, so the query cant possibly be answered.

The queried routers resources are unavailable, generally due to high CPU utilization.

The queried routers memory is corrupt or otherwise unable to allow the router to answer the query.

The link between the two routers is of low quality, allowing just enough packets through to keep the neighbor relationship intact, but not good enough to allow the replies through.

To sum it up, routes generally become SIA when a neighbor either doesnt answer a query, or either the query or reply took a wrong turn somewhere. I told you it wasnt the easiest thing to troubleshoot!

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Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (www.thebryantadvantage.com), home of FREE CCNA and CCNP tutorials and daily exam questions, as well as The Ultimate CCNA and CCNP Study Packages.

For a FREE copy of his latest e-books, “How To Pass The CCNA” or “How To Pass The CCNP”, and for free daily exam question, visit the website and download your copies!

But for BSCI and CCNP exam success, weve got to be able to perform this task.

In a previous tutorial, we saw how to configure RIPv2 packet authentication, with both clear-text and MD5 authentication schemes. EIGRP authentication is much the same, and has the text and MD5 authentication options as well. But EIGRP being EIGRP, the command just has to be a little more detailed!

As with RIPv2, the authentication mode must be agreed upon by the EIGRP neighbors. If one routers interface is configured for MD5 authentication and the remote routers interface is configured for text authentication, the adjacency will fail even if the two interfaces in question are configured to use the same password.

Well now configure link authentication on the adjacency over an Ethernet segment. Below, youll see how to configure a key chain called EIGRP on both routers, use key number 1, and use the key-string BSCI. Run show key chain on a router to see all key chains.

R2(config)#key chain EIGRP

send lifetime (always valid) - (always valid) [valid now]

The EIGRP command to apply the key chain is a bit of a pain to remember, because the protocol and AS number is identified in the middle of the command, not the beginning. Also note that two commands are needed – one to name the key chain, another to define the authentication mode in use.

R2(config)#interface ethernet0

5d07h: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.23.2 (Ethernet0) is up:

As with RIPv2, the existing adjacency was torn down when one side was configured with authentication. If the key chain is correctly defined and applied on both sides, the adjacency will come back up. Always run show ip eigrp neighbor to make sure the adjacency is present. Learn the details of EIGRP key chains by configuring them on your home lab equipment, and youll be more than ready for BSCI exam success!

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Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (www.thebryantadvantage.com), home of FREE CCNA and CCNP tutorials and daily exam questions, as well as The Ultimate CCNA and CCNP Study Packages.

For a FREE copy of his latest e-books, “How To Pass The CCNA” or “How To Pass The CCNP”, and for free daily exam question, visit the website and download your copies!

Route summarization is just one of the many skills youll have to master in order to earn your CCNA. Whether its RIP version 2, OSPF, or EIGRP, the CCNA exam will demand that you can flawlessly configure route summarization.

Route summarization isnt just important for the CCNA exam. Its a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately – what I like to call “concise and complete” routing tables.

The first skill youve got to have in order to work with route summarization is binary math; more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 100.16.0.0 /16, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.0 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article well only illustrate how to convert the first and second octet from decimal to binary.
100 16 = 01100100 00010000

100 17 = 01100100 00010001

100 18 = 01100100 00010010

100 19 = 01100100 00010011

To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which arent used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.

But were not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a “1″ for every bit to the left of the line we drew previously, and a “0″ for every bit to the right. That gives us the following string:

11111111 11111100 00000000 00000000

Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 100.16.0.0 252.0.0.0.

For the CCNA exam, emphasis is put on knowing how to advertise these summary routes in RIPv2 and EIGRP. For both of these protocols, route summarization happens at the interface level – its not configured under the protocol. On the interface that should advertise the summary route, use the command “ip summary-address”. Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.

R1(config-if)#ip summary-address rip 100.16.0.0 255.252.0.0

R1(config-if)#ip summary-address eigrp 100 100.16.0.0 255.252.0.0

The main difference between the two is that the EIGRP command must specify the AS number – thats what the “100″ is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, theres no additional value needed in the configuration.

For OSPF, the commands differ. If youre configuring inter-area route summarization, use the “area range” command; if you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR. Neither of these are interface-level commands.

I speak from experience when I tell you that practice makes perfect on the CCNA exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions – you either know how to do it or you dont. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNA. Heres to your success!

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Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (www.thebryantadvantage.com), home of FREE CCNA and CCNP tutorials and daily exam questions, as well as The Ultimate CCNA and CCNP Study Packages.

For a FREE copy of his latest e-books, “How To Pass The CCNA” or “How To Pass The CCNP”, and for free daily exam question, visit the website and download your copies!