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How to Improve EIGRP Convergence time

To  improve EIGRP convergence time, you can work and manipulate with Feasible Successors, EIGRP Query process, Load balancing etc. I will go through each of them shortly, just to give you hint what parts of the EIGRP can be touched to improve convergence.By having Feasible Successors all the time
You can have situations, wehre you don’t have Feasible successor Routes. An alternate Route to desired destination may present but EIGRP has simply rejected because its Reported Distance (RD) is greater than Feasible Distance (FD) in order to avoid potential loops.Here you can tune EIGRP Metric and convert those Alternate Route into Feasible Successor Routes. By configuring EIGRP so that a Router has Feasible Successor, the whole Query process can be avoided, thus improves EIGRP Convergence incase of Route Failure.

Note:-  Th IOS Command show ip eigrp toplogy, only shows Successors and Feasible Successors.
To check all available route to particular destinations which are neither Successor nor Feasible Successor type this command, show ip eigrp topology all-links
By Configuring Stub Routers and Route Summarization
In some cases Creating a Feasible Successor for all routes on all Routers is impossible, so you can take actions to limit scope of Queries. Here Stub Routers and Route Summarization can help reduce the work performed by the DUAL Algorithm and the scope of Query messages.
Stub Router
Can be defined as, a Router that should not forward traffic between two remote EIGRP-learned subnets.
If a Router is Configured as EIGRP Stub Router, then it doest not advertise EIGRP learned route from one Neighbor to other EIGRP Neighbor, also Non Stub Routers note which EIGRP neighbor is Stub Router and they do not send Query Messages to Stubs Routers. This actions greatly reduces the scope of Query messages when a Route goes active in addition to preventing the long, circitious and possible harmfull Routes.
Route Summarization
If a Router recieves an EIGRP query for a prefix/prefix length, and it does not have an exactly matching route but does have a summary Route that includes the prefix/prefix length, that Router immediately sends an EIGRP reply and does not Flood the Query to its own Neighbors. Thus increasing the Convergence time.
By Load Balancing/Sharing
Load Balancing provides a primary benefit of making use of the available bandwidth, rather than using some links as simply backup links. Fast convergence is a secondary benefit of load balancing in that, if a branch router has two routes for each data center subnet, and one of the route fails, the other route is already in routing table in this case, the router does not need to look for FS routes nor go active on that route. The router uses the usual EIGRP convergence tools only when all such routes are removed from the routing table.
EIGRP Load balancing can be achieved by two methods;
Equal Metric Routes Load balancing
Default by EIGRP which allows four equal metric paths for load balancing, You can define the number of allowed route for each prefix/prefix length using the maximum-paths number EIGRP command. Maximum allowed equal path route with latest IOS are 16.
The Second way of EIGRP Load balancing is by Variance Command.
You can adjust the Route metric by Variance to consider as equal metric path Route for Load balancing. Any FS route whose metric is less than the product of Variance times the FD are considered to be equal Routes and may be placed into the Routing table, upto the Number of Routers defined by the maximum-path EIGRP Command. Variance Number (to be multiplied with metric) can be any number between 1 to 128.


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