Any networker will find it hard to figure out what's wrong with EIGRP SIA routes. Chris Bryant, CCIE #12933, will teach you what you need to know to pass the CCNP exam.
To pass the BSCI exam and get your CCNP, you have to know the details, and there are a lot of details to know about EIGRP SIA routes. If you type "troubleshoot SIA" into a search engine, you'll find a lot of results. Troubleshooting SIA routes is hard because there is no single reason why they happen.
Using the show ip eigrp topology command, you can see a code next to each successor and feasible successor in the EIGRP topology table. People often think that we want these routes to have a "A" next to them to show that they are being used. Isn't that what we want? Sounds like a good idea, doesn't it?
Well, they sound good, but they aren't. If a route is marked as Active in the EIGRP topology table, it means that DUAL is calculating it right now, so it can't be used. When a route starts with "P," it doesn't need to be recalculated and can be used.
Most of the time, a route that is shown as Active will only be there for a short time. By the time you repeat the command, the Active route should have become Passive. When that doesn't happen, the route becomes SIA, which stands for "Stuck In Active."
When a query goes unanswered for so long that the neighbour relationship is reset, the route is said to be SIA. Troubleshooting SIA routes is more of an art than a science, but there are four main reasons why a route becomes SIA:
The link only goes in one direction, so the question can't be answered.
The resources of the router being queried are not available, usually because the CPU is already being used up.
The memory of the queried router is broken or otherwise can't let it answer the query.
The connection between the two routers isn't very good. Just enough packets can get through to keep the neighbour relationship going, but the replies can't get through.
To sum it up, routes generally become SIA when a neighbor either doesn't answer a query, or either the query or reply took a wrong turn somewhere. I told you it wasn't easy to figure out what was wrong.
