Skip to main content

EIGRP technologies


EIGRP technologies
3.1.4

This page will discuss some of the new technologies that EIGRP includes. Each new technology represents an improvement in EIGRP operation efficiency, speed of convergence, or functionality relative to IGRP and other routing protocols. These technologies fall into one of the following four categories:
  • Neighbor discovery and recovery
  • Reliable Transport Protocol
  • DUAL finite-state machine algorithm
  • Protocol-dependent modules
Simple distance vector routers do not establish any relationship with their neighbors. RIP and IGRP routers merely broadcast or multicast updates on configured interfaces. In contrast, EIGRP routers actively establish relationships with their neighbors, much the same way that OSPF routers do.
EIGRP routers establish adjacencies as described in Figure . EIGRP routers use small hello packets to accomplish this. Hellos are sent by default every five seconds. An EIGRP router assumes that as long as it receives hello packets from known neighbors, those neighbors and their routes remain viable or passive. The following are possible when EIGRP routers form adjacencies:
  • Dynamically learn of new routes that join the network
  • Identify routers that become either unreachable or inoperable
  • Rediscover routers that had previously been unreachable
Reliable Transport Protocol (RTP) is a transport layer protocol that guarantees ordered delivery of EIGRP packets to all neighbors. On an IP network, hosts use TCP to sequence packets and ensure their timely delivery. However, EIGRP is protocol-independent. This means it does not rely on TCP/IP to exchange routing information the way that RIP, IGRP, and OSPF do. To stay independent of IP, EIGRP uses RTP as its own proprietary transport layer protocol to guarantee delivery of routing information.
EIGRP can call on RTP to provide reliable or unreliable service as the situation warrants. For example, hello packets do not require the overhead of reliable delivery because they are frequent and should be kept small. The reliable delivery of other routing information can actually speed convergence because then EIGRP routers do not wait for a timer to expire before they retransmit.
With RTP, EIGRP can multicast and unicast to different peers simultaneously. This allows for maximum efficiency.
The centerpiece of EIGRP is the DUAL, which is the EIGRP route-calculation engine. The full name of this technology is DUAL finite-state machine (FSM). An FSM is an algorithm machine, not a mechanical device with parts that move. FSMs define a set of possible states that something can go through, the events that cause those states, and the events that result from those states. Designers use FSMs to describe how a device, computer program, or routing algorithm will react to a set of input events. The DUAL FSM contains all the logic used to calculate and compare routes in an EIGRP network.
DUAL tracks all the routes advertised by neighbors. Composite metrics of each route are used to compare them.   DUAL also guarantees that each path is loop free. DUAL inserts lowest cost paths into the routing table. These primary routes are known as successor routes. A copy of the successor routes is also placed in the topology table.
EIGRP keeps important route and topology information readily available in a neighbor table and a topology table. These tables supply DUAL with comprehensive route information in case of network disruption. DUAL uses the information in these tables to select alternate routes quickly. If a link goes down, DUAL looks for an alternative route path, or feasible successor, in the topology table.
One of the best features of EIGRP is its modular design. Modular, or layered designs, prove to be the most scalable and adaptable. Support for routed protocols, such as IP, IPX, and AppleTalk, is included in EIGRP through PDMs. In theory, EIGRP can add PDMs to easily adapt to new or revised routed protocols such as IPv6.
Each PDM is responsible for all functions related to its specific routed protocol. The IP-EIGRP module is responsible for the following functions:
  • Send and receive EIGRP packets that bear IP data
  • Notify DUAL of new IP routing information that is received
  • Maintain the results of DUAL routing decisions in the IP routing table
  • Redistribute routing information that was learned by other IP-capable routing protocols
The next page will discuss the EIGRP packet types

Comments

Post a Comment

Popular posts from this blog

OSI layers / Peer-to-peer communications / TCP/IP model

OSI layers 2.3.4 This page discusses the seven layers of the OSI model. The OSI reference model is a framework that is used to understand how information travels throughout a network. The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of network media. In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. - Dividing the network into seven layers provides the following advantages: • It breaks network communication into smaller, more manageable parts. • It standardizes network components to allow multiple vendor development and support. • It allows different types of network hardware and software to communicate with each other. • It prevents changes in one layer from affecting other layers. • It divides network communication into smaller parts to make learning it easier to understand. In the foll...
Post a Comment
Read more

Advantages and disadvantages of link-state routing

Advantages and disadvantages of link-state routing 2.1.5  This page lists the advantages and disadvantages of link-state routing protocols. The following are advantages of link-state routing protocols:  Link-state protocols use cost metrics to choose paths through the network. The cost metric reflects the capacity of the links on those paths. Link-state protocols use triggered updates and LSA floods to immediately report changes in the network topology to all routers in the network. This leads to fast convergence times. Each router has a complete and synchronized picture of the network. Therefore, it is very difficult for routing loops to occur. Routers use the latest information to make the best routing decisions. The link-state database sizes can be minimized with careful network design. This leads to smaller Dijkstra calculations and faster convergence. Every router, at the very least, maps the topology of it...
Post a Comment
Read more

Ports for services

Ports for services 10.2.2  Services running on hosts must have a port number assigned to them so communication can occur. A remote host attempting to connect to a service expects that service to use specific transport layer protocols and ports. Some ports, which are defined in RFC 1700, are known as the well-known ports. These ports are reserved in both TCP and UDP.  These well-known ports define applications that run above the transport layer protocols. For example, a server that runs FTP will use ports 20 and 21 to forward TCP connections from clients to its FTP application. This allows the server to determine which service a client requests. TCP and UDP use port numbers to determine the correct service to which requests are forwarded. The next page will discuss ports in greater detail.
Post a Comment
Read more