e query and determines if it has any other feasible successors. If it does not, it has to start a route computation and enter the active state. However in this case, C is a feasible successor because its cost (2) is less than than D's current cost (3) to destination N. D can switch to C as its successor. Note A and C did not participate because they were unaffected by the change.
Now let's cause a route computation to occur. In this scenario, let's say the link between A and C fails. C determines that it has lost its successor and has no other feasible successors. D is not considered a feasible successor because its advertised metric (3) is greater than C's current cost (2) to reach destination N. C must perform a route computation for destination N. C sends a query to its only neighbor D. D replies because its successor has not changed. D does not need to perform a route computation. When C receives the reply it knows that all neighbors have processed the news about the failure to N. At this point, C can choose its new feasible successor D with a cost of (4) to reach destination N. Note that A and B were unaffected by the topology change and D needed to simply reply to C.
Yes, you configure EIGRP just like you configure IGRP. You configure a routing process and which networks the protocol should run over. Existing configuration files can be used.
Yes, there are both protocol independent and dependent debug commands that inform you what the protocol is doing. There is a suite of show commands that give you neighbor table status, topology table status, and EIGRP traffic statistics.
All of the features that you have used in IGRP are available in EIGRP. One feature to point out is multiple routing processes. You can use a single process that runs both IGRP and EIGRP. You can use multiple processes that run both. You can use one process that runs IGRP and another to run EIGRP. You can mix and match. This can help customize your routing to a particular protocol as your needs change.
The bandwidth utilization issue has been addressed by implementing partial and incremental updates. Therefore, only when a topology change occurs does routing information get sent. Regarding processor utilization, the feasible successor technology greatly reduces the total processor utilization of an AS by requiring only the routers that were affected by a topology change to perform the route recomputation. Furthermore, the route recomputation only occurs for routes that were affected. Only those data structures are accessed and used. This greatly reduces search time in complex data structures.
Yes it does. IP-EIGRP performs route aggregation the same way IGRP does. That is, subnets of an IP network are not advertised over another IP network. The subnet routes are summarized into a single network number aggregate. In addition, IP-EIGRP will allow aggregation on any bit boundary in an IP address and can be configured at network interface granularity.
No, a single EIGRP process is analogous to an area of a link-state protocol. However, within the process, information can be filtered and aggregated at any interface boundary. If one wants to bound the propagation of routing information, multiple routing processes can be configured to achieve a hierarchy. Since DUAL itself limits route propagation, multiple routing processes are typically used to define organizational boundaries.