Eigrp routing protocol pdf

Jayaprakash, 2Ms. Different types of routing protocols are applied to specific network environment. EIGRP has the fastest router convergence among the three protocols we are testing. More detailed description of these three routing protocols is included. Misconfiguration of the routing table can cause problems that can interface the data transmissions such as packet loss and delay.

The worst problem that can happen is the loss of important information that is sent. This disorder can occur because the improper configuration of routing tables on the routers, the router device is down, or loss connections between routers. There are two different way to configure routing tables in the router. The routing tables on the routers can be configured by using static routing or active routing.

Used for a Computer network that is not too large, it is advantageous to using static routing. In addition to save router resources, the configuration is not too difficult. When the computer network is larger, the use of static routing will be harder for administrators who are responsible to manage the routing tables. The number of entries in the routing table and also the accuracy of each entry is a key factor for the performance of the computer network.

If there are changes that occur in the topology, routing tables must be updated soon. So the packet sent on the network is not discarded because of an error in the routing table. The classification of routing protocol: The classification of routing protocol is depicted in below. Where there are some dynamic routing protocol can be used to configuring routing tables in the router. Security Considerations IANA Considerations Normative References Informative References DUAL, the algorithm used to converge the control plane to a single set of loop-free paths is based on research conducted at SRI International [ 3 ].

The Diffusing Update Algorithm DUAL is the algorithm used to obtain loop freedom at every instant throughout a route computation [ 2 ]. This allows all routers involved in a topology change to synchronize at the same time; the routers not affected by topology changes are not involved in the recalculation. This document describes the protocol that implements these functions.

Conventions 2. Terminology The following is a list of abbreviations and terms used throughout this document: ACTIVE State: The local state of a route on a router triggered by any event that causes all neighbors providing the current least-cost path to fail the Feasibility Condition check. A route in Active state is considered unusable. During Active state, the router is actively attempting to compute the least-cost loop-free path by explicit coordination with its neighbors using Query and Reply messages.

Address Family Identifier AFI : Identity of the network-layer protocol reachability information being advertised [ 12 ]. Autonomous System AS : A collection of routers exchanging routes under the control of one or more network administrators on behalf of a single administrative entity.

Destinations exchanged within the Base Topology are identified with a Topology Identifier value of zero 0. Computed Distance CD : Total distance metric along a path from the current router to a destination network through a particular neighbor computed using that neighbor's Reported Distance RD and the cost of the link between the two routers.

CR-Mode Conditionally Received Mode Diffusing Computation: A distributed computation in which a single starting node commences the computation by delegating subtasks of the computation to its neighbors that may, in turn, recursively delegate sub-subtasks further, including a signaling scheme allowing the starting node to detect that the computation has finished while avoiding false terminations.

In DUAL, the task of coordinated updates of routing tables and resulting best path computation is performed as a diffusing computation.

Diffusing Update Algorithm DUAL : A loop-free routing algorithm used with distance vectors or link states that provides a diffused computation of a routing table. It works very well in the presence of multiple topology changes with low overhead.

The technology was researched and developed at SRI International [ 3 ]. Downstream Router: A router that is one or more hops away from the router in question in the direction of the destination.

Feasibility Condition: The Feasibility Condition is a sufficient condition used by a router to verify whether a neighboring router provides a loop-free path to a destination. Being effectively a record of the smallest known metric since the last time the network entered the PASSIVE state, the FD is not necessarily a metric of the current best path.

Exactly one FD is computed per destination network. Feasible Successor: A neighboring router that meets the Feasibility Condition for a particular destination, hence, providing a guaranteed loop-free path.

The ability of two routers to become neighbors depends on their mutual connectivity and compatibility of selected EIGRP configuration parameters. Two neighbors with interfaces connected to a common subnet are known as adjacent neighbors. Two neighbors that are multiple hops apart are known as remote neighbors. Network Layer Reachability Information NLRI : Information a router uses to calculate the global routing table to make routing and forwarding decisions.

Reported Distance RD : For a particular destination, the value representing the router's distance to the destination as advertised in all messages carrying routing information.

RD is not equivalent to the current distance of the router to the destination and may be different from it during the process of path re-computation. Exactly one RD is computed and maintained per destination network. Sub-Topology: For a given Base Topology, a sub-topology is characterized by an independent set of routers and links in a network for which EIGRP performs an independent path calculation. This allows each sub- topology to implement class-specific topologies to carry class- specific traffic.

Successor-Directed Acyclic Graph SDAG : For a particular destination, a graph defined by routing table contents of individual routers in the topology, such that nodes of this graph are the routers themselves and a directed edge from router X to router Y exists if and only if router Y is router X's successor. After the network has converged, in the absence of topological changes, SDAG is a tree.

Topology Identifier TID : A number that is used to mark prefixes as belonging to a specific sub-topology. Each TLV-formatted information element consists of three generic fields: Type identifying the nature of information carried in this element, Length describing the length of the entire TLV triplet, and Value carrying the actual information.

The Value field may, itself, be internally structured; this depends on the actual type of the information element. This format allows for extensibility and backward compatibility. Upstream Router: A router that is one or more hops away from the router in question, in the direction of the source of the information. DUAL guarantees that each constructed path is loop free at every instant including periods of topology changes and network reconvergence. This is accomplished by all routers, which are affected by a topology change, computing the new best path in a coordinated diffusing way and using the Feasibility Condition to verify prospective paths for loop freedom.

Routers that are not affected by topology changes are not involved in the recalculation. The convergence time with DUAL rivals that of any other existing routing protocol. Only nodes that are affected by a topology change need to propagate and act on information about the topology change, allowing EIGRP to have good scaling properties, reduced overhead, and lower complexity than many other interior gateway protocols.

Distributed routing algorithms are required to propagate information as well as coordinate information among all nodes in the network. Unlike basic Bellman-Ford distance vector protocols that rely on uncoordinated updates when a topology change occurs, DUAL uses a coordinated procedure to involve the affected part of the network into computing a new least-cost path, known as a "diffusing computation". A diffusing computation grows by querying additional routers for their current RD to the affected destination, and it shrinks by receiving replies from them.

Unaffected routers send replies immediately, terminating the growth of the diffusing computation over them. These intrinsic properties cause the diffusing computation to self-adjust in scope and terminate as soon as possible. One attribute of DUAL is its ability to control the point at which the diffusion of a route calculation terminates by managing the distribution of reachability information through the network.

This provides the ability to create effective failure domains within a single AS, and allows the network administrator to manage the convergence and processing characteristics of the network.

Consequently, in PASSIVE state, the router does not perform any route recalculation in coordination with its neighbors because no such recalculation is needed. In ACTIVE state, the router is actively involved in re-computing the least-cost loop-free path in coordination with its neighbors. The state is reevaluated and possibly changed every time a topology change is detected.

A topology change is any event that causes the CD to the destination over any neighbor to be added, changed, or removed from EIGRP's topology table. More exactly, the two states are defined as follows: o Passive A route is considered to be in the Passive state when at least one neighbor that provides the current least-total-cost path passes the Feasibility Condition check that guarantees loop freedom.

A route in the ACTIVE state is considered unusable and this router must coordinate with its neighbors in the search for the new loop- free least-total-cost path. Feasible Successors providing the least-total-cost path are also called "successors". While these neighbors are guaranteed to provide a loop-free path, that path is potentially not the shortest available. The fact that the least-total-cost path can be provided by a neighbor that fails the Feasibility Condition check may not be intuitive.

However, such a situation can occur during topology changes when the current least-total-cost path fails and the next-least-total-cost path traverses a neighbor that is not a Feasible Successor. Feasibility Condition The Feasibility Condition is a criterion used to verify loop freedom of a particular path. The Feasibility Condition is a sufficient but not a necessary condition, meaning that every path meeting the Feasibility Condition is guaranteed to be loop free; however, not all loop-free paths meet the Feasibility Condition.

Based on the result of the Feasibility Condition check after a topology change is detected, the route may either remain PASSIVE if, after the topology change, the neighbor providing the least cost path meets the Feasibility Condition or it needs to enter the ACTIVE state if the topology change resulted in none of the neighbors providing the least cost path to meet the Feasibility Condition. Nodes that are not affected by the topology change are not required to perform a DUAL computation and may not be aware a topology change occurred.

This can occur in two cases: Savage, et al. A route that meets the Feasibility Condition is determined to be loop free and downstream along the path between the router and the destination. Second, if informed about a topology change for which it does not currently have reachability information, a router is not required to enter into the ACTIVE state, nor is it required to participate in the DUAL process.

In order to facilitate describing the Feasibility Condition, a few definitions are in order. Typically, the successor is chosen based on the least-cost path to reach the destination. A Feasible Successor is regarded as a downstream neighbor towards the destination, but it may not be the least-cost path but could still be used for forwarding data packets in the event equal or unequal cost load sharing was active.

A Feasible Successor can become a successor when the current successor becomes unreachable. It should be noted it is not necessarily the current best distance; rather, it is a historical record of the best distance known since the last diffusing computation for the destination has finished.

Thus, the value of the FD can either be the same as the current best distance, or it can be lower. A neighbor that advertises a route with a cost that does not meet the Feasibility Condition may be upstream and thus cannot be guaranteed to be the next hop for a loop-free path.

Routes advertised by upstream neighbors are not recorded in the routing table but saved in the topology table. It tracks all routes advertised by all neighbors.

The distance information, known as a metric, is used by DUAL to select efficient loop-free paths. A successor is a neighboring router used for packet forwarding that has a least-cost path to a destination that is guaranteed not to be part of a routing loop. When there are no Feasible Successors but there are neighbors advertising the destination, a recalculation must occur to determine a new successor. Even though the recalculation is not processor intensive, it is advantageous to avoid recalculation if it is not necessary.

If there are Feasible Successors, it will use any it finds in order to avoid any unnecessary recalculation. The FSM, which applies per destination in the topology table, operates independently for each destination. However, a separate SDAG is computed for each destination, so loop- free topologies can be maintained for each reachable destination. Split horizon takes effect for a query or update from the successor it is using for the destination in the query. The route stays in ACTIVE state if there are more replies pending because the router has not heard from all neighbors.

Each node is labeled with its costs to destination N. The arrows indicate the successor next hop used to reach destination N. The least-cost path is selected. C determines that it has a Feasible Successor and replies immediately with metric 3. D now has a viable path to N through C. D selects C as its successor to reach node N with a cost of 4. Notice that nodes A and B were not involved in the recalculation since they were not affected by the change.

Note that nodes A and D were not involved in the recalculation since their successors were not affected. Each packet transmitted will use either multicast or unicast network- layer destination addresses. When multicast addresses are used, a mapping for the data link multicast address when available must be provided.

The source address will be set to the address of the sending interface, if applicable. The following network-layer multicast addresses and associated data link multicast addresses: Network-layer addresses will be used and the mapping to media addresses will be achieved by the native protocol mechanisms. When a new neighbor is discovered, unicast UPDATE packets are used to transmit a full table to the new neighbor, so the neighbor can build up its topology table.

An infinite metric is encoded by setting the delay part of the metric to its maximum value. When a REPLY packet is received, there is no reason to process the packet before an acknowledgment is sent.

Therefore, an acknowledgment is sent immediately and then the packet is processed. The sending of the acknowledgment is accomplished either by sending an ACK packet or by piggybacking the acknowledgment onto another packet already being transmitted. Exception Handling 4. Any neighbor that fails to send Savage, et al. Implementation note: Cisco currently implements option b. 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. Till route1 is available, it will not insert route2 in routing table.

When route1 is down, it will look for next possible route. If other routes are available, it will replace current route with new route which has the lowest metric value. We can watch this process live with debug eigrp fsm command. On debug process on Router0. Now suppose route1 is down. EIGRP will look in topology table for next available routes. If single alternative is available, it will be selected.

If multiple routes are available, it will select the route with the lowest metric value. We do not accept any kind of Guest Post. Except Guest post submission, for any other query such as adverting opportunity, product advertisement, feedback, suggestion, error reporting and technical issue or simply just say to hello mail us ComputerNetworkingNotes gmail.

Router config. Router configure terminal Enter configuration commands, one per line. Router config-router network Router config router eigrp 20 Router config-router network Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. Bahman Xalid. A short summary of this paper. Introduction to the Configuration Exercises This book uses Configuration Exercises to help you practice configuring routers with the commands and topics presented.

If you have access to real hardware, you can try these exercises on your routers. See Appendix B, "Configuration Exercise Equipment Requirements and Backbone Configurations," for a list of recommended equipment and initial configuration commands for the backbone routers. However, even if you do not have access to any routers, you can go through the exercises, and keep a log of your own running configurations, or just read through the solution.

Commands used and solutions to the Configuration Exercises are provided within the exercises. In the Configuration Exercises, the network is assumed to consist of two pods, each with four routers. The pods are interconnected to a backbone. You configure pod 1.