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# How does variance work in EIGRP?

## How does variance work in EIGRP?

EIGRP provides a mechanism to load balance over unequal cost paths throungh Variance Command. Variance is a number (1 to 128), multiplied by the local best metric then includes the routes with the lesser or equal metric. The default Variance value is 1, which means equal-cost load balancing.

### What are the EIGRP K values?

K-Values and EIGRP Metrics

K Value Component Description
K1 Bandwidth Lowest bandwidth of route
K3 Delay Cumulative interface delay of route
K4 Reliability Worst reliability of route based on keep alive

How is EIGRP metric calculated?

EIGRP uses these scaled values to determine the total metric to the network: metric = [K1 * bandwidth + (K2 * bandwidth) / (256 – load) + K3 * delay] * [K5 / (reliability + K4)]

How does EIGRP calculate feasible distance?

feasible distance: Best metric among all path to a network. It is calculated by adding the advertised/reported distance advertised by the neighbor and the cost calculated by that current router to reach the neighbor. successor: It is the (lowest) best path to reach to any specific destination network.

## What is EIGRP load balancing?

By default, EIGRP supports equal-cost load balancing over four links. Equal-cost means that multiple routes must have the same metric to reach the destination, so that router can choose to load balance across equal cost links. Router R1 places both routes in the routing table and load balances across three links.

### What is EIGRP metric?

EIGRP determines the value of the path using five metrics: bandwidth, load, delay, reliability and MTU. EIGRP uses Five different messages to communicate with its neighbor routers. EIGRP messages are Hello, Update, Query, Reply, and Acknowledgement.

How does EIGRP determine k values?

The formula for the computation of EIGRP metric is – It’s important to understand where to find the EIGRP k values in the Cisco network devices. The command “show interfaces (interface name)” will provide the detail of all the K-values i.e. Bandwidth, Load, delay, Reliability and MTU.

What algorithm does EIGRP use?

diffusing update algorithm
EIGRP uses a diffusing update algorithm (DUAL) to identify network paths and provides for fast convergence using precalculated loop-free backup paths. Most distance vector routing protocols use hop count as the metric for routing decisions.

## What is reported distance in EIGRP?

Feasible distance (FD) – the metric of the best route to reach a network. That route will be listed in the routing table. Reported distance (RD) – the metric advertised by a neighboring router for a specific route. It other words, it is the metric of the route used by the neighboring router to reach the network.

One of the advantages of EIGRP is that, unlike OSPF and many other routing protocols, EIGRP also supports unequal-cost load balancing. You can set up your router to load balance over links with different metric to reach the destination. To accomplish unequal-cost load balancing, the variance command is used.

What is EIGRP delay?

EIGRP delay is set on an interface-by-interface basis, allowing for manipulation of traffic patterns flowing through a specific interface on a router. Delay is configured with the interface parameter command delay tens-of-microseconds under the interface.

What is the variance of the EIGRP value?

The EIGRP variance value is the feasible distance (FD) for a route multiplied by the EIGRP variance multiplier. Any feasible successor’s FD with a metric below the EIGRP variance value is installed into the RIB.

## How is the metric calculation done in EIGRP?

Metric calculation is a critical component for any routing protocol. EIGRP uses multiple factors to calculate the metric for a path. Metric calculation uses bandwidth and delay by default but can include interface load and reliability, too. The formula shown in Figure 2-6 illustrates the EIGRP classic metric formula.

### How does the variance command work in IGRP?

Use the variance n command in order to instruct the router to include routes with a metric of less than n times the minimum metric route for that destination. The variable n can take a value between 1 and 128.

Which is EIGRP route qualifies for unequal cost load sharing?

By setting the EIGRP variance to 2 on R1, any route to 2.2.2.0 /24 with a metric of less than 4595712 (2 x 2297856) will be entered into the EIGRP routing table and will participate in unequal-cost load sharing. The only feasible successor to that route has a metric of 2300416, so it certainly qualifies!