Administering Cisco QoS for IP Networks
Tweak and tune your Cisco routers for best performance with this practical guide.
TABLE OF CONTENTS Administering Cisco QoS for IP Networks
Recognizing Caveats
While EIGRP is a relatively mature protocol, it maintains several very important caveats that you must be aware of when designing and implementing an EIGRP network. I will briefly discuss the nature of these caveats and then provide troubleshooting examples in the next section.
Stuck-in-Active
One of the most common and well-known caveats of EIGRP is the Stuck-in-Active (SIA) route. While one of the main design goals of EIGRP was to create a fast converging protocol, it was realized that a diffused computation could be delayed indefinitely due to factors outside the protocol s own mechanisms. If the best decision is to be made, it must be made from all available information. Therefore, when a route needs to be selected or recalculated, a router must attempt to gather the best information available from its neighbors.
The architects of EIGRP designed it in such a way that no routing decisions will be made until all neighbors have had a chance to participate in the decision-making process. What should happen if a neighbor fails to respond to a query? The decision was made to declare the neighbor dead after an active timer expires, approximately 3 minutes. It could be argued that only the loss of hellos should cause a neighbor to be declared dead. After all, if the router does not respond to a query, won t it have stopped sending hellos? Simply stated: No.
To understand why a router may still be able to send hellos but not respond to...
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