EIGRP can be configured for other features, like Message Digest 5 MD5 authentication, to accept routing information only from trusted neighbors, automatic and manual summarization of routes and equal and unequal cost load balancing. It can filter incoming and outgoing updates, as well as adjust the metric of transmitted and received routes. Basic Configuration Example:. First go to router process mode, the process number should be same on all devices to form neighbor relationship between them.
R1 conf t. R1 config router eigrp 1. R1 config-router. Then if you have to run EIGRP on the interfaces,specify each network with wildcard mask for every interface:. R1 config-router network R1 config-router network 1. R1 config-if ip authentication mode eigrp 1 md5. R1 config-if ip authentication key-chain eigrp 1 cisco. R1 config-if ip bandwidth-percent eigrp 1 R1 config ipv6 router eigrp 1. R1 config-rtr eigrp router-id Use Cisco Feature Navigator to find information about platform support and Cisco software image support.
To access Cisco Feature Navigator, go to www. An account on Cisco. Fast convergence--The DUAL algorithm allows routing information to converge as quickly as any currently available routing protocol. Partial updates--EIGRP sends incremental updates when the state of a destination changes, instead of sending the entire contents of the routing table.
Neighbor discovery mechanism--This simple protocol-independent hello mechanism is used to learn about neighboring devices. A virtual routing and forwarding VRF instance and a route distinguisher must be defined before the address family session can be created.
When the address family is configured, we recommend that you configure an autonomous system number either by using the autonomous-system-number argument with the address-family command or by using the autonomous-system command. An EIGRP named configuration does not create an EIGRP routing instance by itself; it is a base configuration that is required to define address-family configurations that are used for routing.
A VRF instance and a route distinguisher must be defined before the address family session can be created. The number of VRFs that can be configured is limited only by the available system resources on the device, which is determined by the number running processes and available memory. Neighbor relationship maintenance is the process that devices use to dynamically learn of other devices on their directly attached networks. Devices must also discover when their neighbors become unreachable or inoperative.
Neighbor relationship maintenance is achieved with low overhead by devices when they periodically send small hello packets to each other. As long as hello packets are received, the Cisco software can determine whether a neighbor is alive and functioning. After the status of the neighbor is determined, neighboring devices can exchange routing information. The reliable transport protocol supports intermixed transmission of multicast and unicast packets. Some EIGRP packets such as updates must be sent reliably; this means that the packets require acknowledgment from the destination.
For efficiency, reliability is provided only when necessary. For example, on a multiaccess network that has multicast capabilities, hello packets need not be sent reliably to all neighbors individually. Therefore, EIGRP sends a single multicast hello packet with an indication in the packet informing receivers that the packet need not be acknowledged.
The reliable transport protocol can send multicast packets quickly when unacknowledged packets are pending, thereby ensuring that the convergence time remains low in the presence of varying speed links.
Some EIGRP remote unicast-listen any neighbor that uses unicast to communicate and remote multicast-group neighbors may peer with any device that sends a valid hello packet, thus causing security concerns. By authenticating the packets that are exchanged between neighbors, you can ensure that a device accepts packets only from devices that know the preshared authentication key. The authentication of packets being sent between neighbors ensures that a device accepts packets only from devices that have the same preshared key.
If this authentication is not configured, you can intentionally or accidentally add another device to the network or send packets with different or conflicting route information onto the network, resulting in topology corruption and denial of service DoS. Enhanced Interior Gateway Routing Protocol EIGRP authentication is configurable on a per-interface basis; packets exchanged between neighbors connected through an interface are authenticated.
EIGRP supports message digest algorithm 5 MD5 authentication to prevent the introduction of unauthorized information from unapproved sources. MD5 authentication is defined in RFC The DUAL finite state machine embodies the decision process for all route computations.
It tracks all routes advertised by all neighbors. DUAL uses the distance information known as the metric to select efficient, loop-free paths. DUAL selects routes to be inserted into a routing table based on feasible successors. A successor is a neighboring device used for packet forwarding that has the least-cost path to a destination that is guaranteed not to be part of a routing loop. When there are no feasible successors but only neighbors advertising the destination, a recomputation must occur to determine a new successor.
The time required to recompute the route affects the convergence time. Recomputation is processor-intensive, and unnecessary recomputation must be avoided.
When a topology change occurs, DUAL will test for feasible successors. If there are feasible successors, DUAL will use any feasible successors it finds to avoid unnecessary recomputation.
Protocol-dependent modules are responsible for network-layer protocol-specific tasks. The goodbye message is broadcast when an EIGRP routing process is shut down to inform adjacent peers about an impending topology change. This feature allows supporting EIGRP peers to synchronize and recalculate neighbor relationships more efficiently than would occur if the peers discovered the topology change after the hold timer expired.
The following message is displayed by devices that run a supported release when a goodbye message is received:. A Cisco device that runs a software release that does not support the goodbye message can misinterpret the message as a K-value mismatch and display the following error message:. The receipt of a goodbye message by a nonsupporting peer does not disrupt normal network operation. The nonsupporting peer terminates the session when the hold timer expires.
The sending and receiving devices reconverge normally after the sender reloads. EIGRP metric defaults K values have been carefully selected to provide optimal performance in most networks. Because of the complexity of this task, we recommend that you do not change the default K values without guidance from an experienced network designer.
By default, the EIGRP composite cost metric is a bit quantity that is the sum of segment delays and the lowest segment bandwidth scaled and inverted for a given route. For a network of homogeneous media, this metric reduces to a hop count. For a network of mixed media FDDI, Gigabit Ethernet GE , and serial lines running from bits per second to T1 rates , the route with the lowest metric reflects the most desirable path to a destination. Mismatched K values can prevent neighbor relationships from being established and can negatively impact network convergence.
The following configuration is applied to Device-A. The K values are changed using the metric weights command. A value of 2 is entered for the k1 argument to adjust the bandwidth calculation. A value of 1 is entered for the k3 argument to adjust the delay calculation. The following configuration is applied to Device-B, and the default K values are used. The default K values are 1, 0, 1, 0, 0, and 0. The bandwidth calculation is set to 2 on Device-A and set to 1 by default on Device-B.
This configuration prevents these peers from forming a neighbor relationship. The following error message is displayed on the console of Device-B because the K values are mismatched:. Two devices are connected on the same link and configured to establish a neighbor relationship. However, each device is configured with different K values.
The receiving device will interpret this message as a K-value mismatch. An offset list is a mechanism for increasing incoming and outgoing metrics to routes learned via EIGRP.
Optionally, you can limit the offset list with either an access list or an interface. Offset lists are available only in IPv4 configurations. IPv6 configurations do not support offset lists. To avoid churn in the network as a result of a change in the link characteristics, a tunable dampening mechanism is used. EIGRP uses metric weights along with a set of vector metrics to compute the composite metric for local RIB installation and route selections.
EIGRP uses one or more vector metrics to calculate the composite cost metric. The minimum bandwidth of the route, in kilobits per second. With wildcard we are no longer limited with default boundaries.
We can match Subnetted networks as well as default networks. For example we were tasked to exclude serial interfaces in above configuration. We can use a wildcard mask of 0. Now router will look for Our serial interfaces have If you are unfamiliar with wildcard mask, I suggest you to read our tutorials on ACL where we explained wildcard mask in detail with examples.
Until you learn wildcard mask, use subnet mask in the place of wildcard mask. Subnet mask is a substitute, not a replacement of wildcard mask. When we use Subnet mask, router converts them in wildcard mask before searching for associated interfaces.
We can look in running configuration to know what exactly being used by router. If you are a CCNA candidate or preparing for any Cisco certification, I suggest you to use wildcard mask instead of Subnet mask with network command.
In real life implementation you can use either subnet mask or wildcard mask. If you use wildcard, it will be used as it is. If you use subnet mask, it will be converted in wildcard mask before using.
As I mentioned earlier, we can use both wildcard mask and subnet mask with network command. We have used wildcard mask for above routers.
In remaining routers we will use subnet mask. To verify the setup we will use ping command. We have two routes between source and destination. Access the command prompt of PC1 and use ping command to test the connectivity from Server0. After that use tracert command to print the taken path. If you are not getting same output download this configured topology and cross check with your topology to figure out the reason.
EIGRP protocol automatically manages all routes for us. If one route goes down, it will automatically switch to another available route. To explain this process more clearly we have added one additional route in our network. You may wonder where Route2 is in this output. You should enter this command for each network directly attached to the router.
However, you can, in a single statement, enter the supernet of a group of subnets. When you do that, the router will automatically identify the subnets. Once EIGRP is configured, you can check the status using the show ip route and show ip eigrp commands. Here are some examples:. There are a number of show ip eigrp xxxx commands.
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