The chapter discusses EIGRP and OSPF routing protocols. It provides information on configuring and verifying EIGRP, including EIGRP tables, metrics, neighbor discovery using hello packets, and terminology such as feasible successors. It also covers configuring and verifying OSPF, as well as using wildcards.
EIGRP is a cisco proprietary, Advance distance vector, classless Interior gateway routing protocol.
Released in-1994.
It works on Network Layer of OSI Model.
It use the IP protocol no 88. (It doesn’t use TCP or UDP)
EIGRP AD – 90
Eigrp External routes AD – 170
EIGRP has a maximum hop-count of 224, though the default maximum hop-count is set to 100
Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration.
The document discusses routing protocols including EIGRP, OSPF, and BGP. It covers topics such as configuration, terminology, route selection processes, and attributes for each protocol. The objectives are to understand how these protocols work, configure various features, and troubleshoot routing issues.
EIGRP is a hybrid routing protocol that uses both distance-vector and link-state characteristics. It uses DUAL algorithm for routing calculations and loop prevention. EIGRP sends periodic hello packets to discover neighbors and non-periodic updates when routes change. The default EIGRP metric is the minimum bandwidth on a path plus the sum of the delays. Show commands can be used to display EIGRP neighbor information, topology tables, route tables, traffic statistics, and event/packet details for troubleshooting.
EIGRP is a proprietary routing protocol developed by Cisco that is based on distance-vector routing. It uses the Diffusing Update Algorithm to quickly converge on routes and prevent routing loops. EIGRP calculates composite metrics for routes using factors like bandwidth and delay to determine the best path. It elects successors and feasible successors for routes to provide primary and backup paths. EIGRP also uses neighbor tables, topology tables, and routing tables to store routing information and make forwarding decisions.
The document discusses the key concepts of EIGRP including its hybrid nature, neighbor establishment process, metric calculations, and use of successors and feasible successors. EIGRP forms neighbor relationships by exchanging Hello packets to verify matching AS numbers and K-values. It calculates metrics based on bandwidth, delay, and other configurable factors, and uses the DUAL algorithm to determine the best path and maintain backup paths as feasible successors to speed convergence.
Building Scalable Cisco Internetworks (Bsci)CCNAResources
This document provides a summary of key topics about the Building Scalable Cisco Internetworks (BSCI) 642-901 exam, including routing protocols like EIGRP, OSPF, and BGP. It outlines the contents, objectives, and recommends additional reading and hands-on practice to fully prepare for the exam. The summary is intended to help remember topics, but not replace learning the foundational knowledge required to pass.
EIGRP is a cisco proprietary, Advance distance vector, classless Interior gateway routing protocol.
Released in-1994.
It works on Network Layer of OSI Model.
It use the IP protocol no 88. (It doesn’t use TCP or UDP)
EIGRP AD – 90
Eigrp External routes AD – 170
EIGRP has a maximum hop-count of 224, though the default maximum hop-count is set to 100
Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration.
The document discusses routing protocols including EIGRP, OSPF, and BGP. It covers topics such as configuration, terminology, route selection processes, and attributes for each protocol. The objectives are to understand how these protocols work, configure various features, and troubleshoot routing issues.
EIGRP is a hybrid routing protocol that uses both distance-vector and link-state characteristics. It uses DUAL algorithm for routing calculations and loop prevention. EIGRP sends periodic hello packets to discover neighbors and non-periodic updates when routes change. The default EIGRP metric is the minimum bandwidth on a path plus the sum of the delays. Show commands can be used to display EIGRP neighbor information, topology tables, route tables, traffic statistics, and event/packet details for troubleshooting.
EIGRP is a proprietary routing protocol developed by Cisco that is based on distance-vector routing. It uses the Diffusing Update Algorithm to quickly converge on routes and prevent routing loops. EIGRP calculates composite metrics for routes using factors like bandwidth and delay to determine the best path. It elects successors and feasible successors for routes to provide primary and backup paths. EIGRP also uses neighbor tables, topology tables, and routing tables to store routing information and make forwarding decisions.
The document discusses the key concepts of EIGRP including its hybrid nature, neighbor establishment process, metric calculations, and use of successors and feasible successors. EIGRP forms neighbor relationships by exchanging Hello packets to verify matching AS numbers and K-values. It calculates metrics based on bandwidth, delay, and other configurable factors, and uses the DUAL algorithm to determine the best path and maintain backup paths as feasible successors to speed convergence.
Building Scalable Cisco Internetworks (Bsci)CCNAResources
This document provides a summary of key topics about the Building Scalable Cisco Internetworks (BSCI) 642-901 exam, including routing protocols like EIGRP, OSPF, and BGP. It outlines the contents, objectives, and recommends additional reading and hands-on practice to fully prepare for the exam. The summary is intended to help remember topics, but not replace learning the foundational knowledge required to pass.
The document provides information on Cisco Nexus 5000 Layer 3 switching including:
- An overview of EIGRP fundamentals such as neighbor discovery, route metrics, and the Diffusing Update Algorithm.
- Details on EIGRP configuration and operation in NX-OS versus IOS including differences in CLI, route redistribution, and VRF support.
- Configuration examples that highlight similarities and differences between NX-OS and IOS for EIGRP tasks like interface configuration, authentication, and summarization.
This document provides an overview of the network layer and some of its key protocols. It begins with an introduction to the network layer and its main responsibilities, including routing packets between subnets that may have different addressing schemes or protocols. It then discusses some of the network layer's main functionalities and features. The remainder of the document defines and describes several important network layer protocols, including EIGRP, ICMP, IGMP, IPv4, and others. It provides high-level explanations of how these protocols function and their roles within the network layer.
EIGRP is a proprietary routing protocol developed by Cisco that uses a composite metric and has fast convergence properties. It functions as a hybrid of distance-vector and link-state routing protocols, sending subnet mask and VLSM information in updates. EIGRP forms neighbor relationships through periodic hello messages and establishes three key tables - Neighbor, Topology, and Routing - to store neighbor, route, and best path information. It utilizes five packet types and reliable transport to efficiently share routing updates.
IGRP and EIGRP.
Comparison between traditional Distance Vector Routing Protocols and Enhanced Distance Vector Routing Protocols.
EIGRP Message Format and Packet Header.
EIGRP Parameters (K1,K2, K3, K4, K5, Reserved, and Hold Time).
Protocol Dependent Modules (PDM).
Reliable Transport Protocol (RTP).
EIGRP Packet Types (Hello Packets, Update packets, Acknowledgment packets, Query and Reply packets).
EIGRP Bounded Updates.
Introduction to DUAL Algorithm.
EIGRP Administrative Distance.
The router eigrp Command, the network command with a Wildcard Mask, Verifying EIGRP and using the Bandwidth command
EIGRP Metric Calculation, EIGRP uses Bandwidth, delay, reliability, and load in its metric.
DUAL Concepts, successor, Feasible distance (FD), Feasible successor (FS), Reported distance (RD)/ AD and Feasibility Condition (FC).
DUAL Finite State Machine, Null0 Summary Route, Disabling Automatic Summarization, Manual Summarization and EIGRP default route
EIGRP is an enhanced interior gateway routing protocol that has characteristics of both distance vector and link state routing. It supports features like classless routing, VLSM, route summarization, incremental updates, and load balancing. The maximum hop count for EIGRP is 224 and it uses the multicast address 224.0.0.10. EIGRP applies an administrative distance of 90 for internal routes and 170 for external routes.
- An autonomous system (AS) is a group of networks under single administrative control, each with a unique ID number. Interior gateway protocols (IGPs) like RIP, IGRP, EIGRP, OSPF route within an AS, while exterior gateway protocols like BGP route between ASes.
- IGRP is a distance vector protocol that uses a composite metric and broadcasts updates. EIGRP is an advanced hybrid protocol that uses multicast updates and three tables to store routing information. OSPF is a link-state protocol that forms adjacencies and uses areas and least-cost routing.
- Configuring these protocols involves enabling IP routing, specifying the routing protocol and associated networks, and verifying
Presentation about interior gateway routing protocol EIGRP which covers most of the concepts and features of the protocol.
Delivered by Dmitry Figol, CCIE R&S #53592.
The document provides an overview of the Border Gateway Protocol (BGP). It begins with general information about BGP, including that it is used for routing between autonomous systems and is classified as a path vector routing protocol. It then covers BGP theory in detail over several sections, explaining concepts like neighbors, messages, states, attributes and more. The document aims to provide thorough theoretical understanding needed to implement BGP in a lab.
EIGRP is an enhanced distance vector routing protocol developed by Cisco that provides faster convergence properties and lower usage of bandwidth compared to IGRP. EIGRP forms neighbor relationships to dynamically learn of route changes and failures. It uses the Diffusing Update Algorithm (DUAL) to select optimal routes and maintain three tables - the neighbor table, topology table, and routing table. EIGRP supports classless routing, variable length subnet masking, and multi-protocol routing. It provides rapid convergence, efficient bandwidth usage, and independence from routed protocols through features like partial route updates, hello packets, and protocol-dependent modules.
Packet Tracer: Routing protocols EIGRP and OSPFRafat Khandaker
The document summarizes an experiment in Packet Tracer where the routing protocols EIGRP and OSPF were implemented on a simulated enterprise network with multiple hosts and routers. EIGRP and OSPF were configured on the 3 routers to exchange routing update tables and allow routing between all hosts. The experiment demonstrated how each protocol operates, including configuration of EIGRP with autonomous system numbers and OSPF with areas to establish routing adjacencies between routers. Pings between hosts across the routers confirmed correct routing was achieved with both protocols.
This document provides an overview of the Enhanced Interior Gateway Routing Protocol (EIGRP). It describes the history and development of EIGRP, its basic operation and components, including reliable transport protocol, packet types, neighbor discovery via hello packets, and route updates using the diffusing update algorithm. It also covers basic EIGRP configuration such as enabling it with the router eigrp command, advertising networks, and verifying neighbor relationships.
Dynamic Routing All Algorithms, Working And BasicsHarsh Mehta
This document provides information on computer networks and routing protocols. It discusses advantages and problems of computer networks. It then describes the Enhanced Interior Gateway Routing Protocol (EIGRP) and some of its key features like security, congestion handling, efficiency, and support for IPv4 and IPv6. It also discusses static and dynamic routing, different routing metrics, and compares EIGRP to other routing protocols like RIP, OSPF, and IS-IS.
Route redistribution involves sharing routes between different routing protocols. Challenges include incompatible metrics between protocols and routing loops or suboptimal paths that can occur from redistributing routes back into their origin domain. Route maps, distribution lists, and adjusting administrative distances can control redistribution and prevent issues like feedback of routes into their source protocol.
Redistribution is necessary when routing protocols connect and must pass routes between the two.
Route Redistribution involves placing the routes learned from one routing domain, such as RIP, into
another routing domain, such as EIGRP.
While running a single routing protocol throughout your entire IP internetwork is desirable, multiprotocol routing is common for a number of reasons, such as company mergers, multiple departments
managed by multiple network administrators, and multi-vendor environments. Running different
routing protocols is often part of a network design.
Lecture number 5 Theory.pdf(machine learning)ZainabShahzad9
This document discusses computer networks and routing protocols. It provides an overview of key topics including:
- The difference between routed protocols like IPv4 and IPv6 that transfer user data, and routing protocols like RIP and OSPF that send route update packets.
- Common routing and routed protocols including IGPs, EGPs, RIP, OSPF, EIGRP and BGP.
- Desirable properties of routing algorithms such as correctness, robustness, stability, fairness and efficiency.
- Types of routing including fixed, flooding, dynamic and default routing. Characteristics of distance vector and link state routing protocols are also outlined.
Performance Analysis of Routing Protocols RIP, OSPF and EIGRPIRJET Journal
This document analyzes the performance of three routing protocols: RIP, OSPF, and EIGRP. It simulates these protocols using GNS3 software and analyzes parameters like convergence time, end-to-end delay, and throughput. Redistribution between the protocols is implemented using configuration commands. Ping tests and Wireshark analysis show packet forwarding between networks running different protocols. Analysis finds that EIGRP has the best performance with low convergence time and delay compared to RIP and OSPF in the simulated networks.
The document discusses various topics relating to EIGRP implementation including:
- Establishing EIGRP neighbor relationships and different network environments where EIGRP can operate like Frame Relay and MPLS networks.
- Building the EIGRP topology table by exchanging routing information with neighbors, calculating EIGRP metrics and selecting the best path.
- Optimizing EIGRP behavior such as using stub routing and route summarization to reduce queries when a route becomes active.
The document provides an overview of configuring the Enhanced Interior Gateway Routing Protocol (EIGRP). It describes the basic operation and components of EIGRP, including its tables, metrics, neighbor discovery, and packet types. The objectives are to describe EIGRP functionality, plan and implement EIGRP routing, and configure and verify EIGRP implementations in enterprise networks.
This chapter discusses the configuration of the Enhanced Interior Gateway Routing Protocol (EIGRP). It describes the basic operation and terminology of EIGRP, including its tables, metrics, and routing behavior. The chapter also covers EIGRP packet types, neighbor discovery, route calculation using the DUAL algorithm, and key technologies such as reliable transport and protocol-dependent modules. The overall purpose is to explain how to plan, implement, configure and verify EIGRP routing.
The document provides information on Cisco Nexus 5000 Layer 3 switching including:
- An overview of EIGRP fundamentals such as neighbor discovery, route metrics, and the Diffusing Update Algorithm.
- Details on EIGRP configuration and operation in NX-OS versus IOS including differences in CLI, route redistribution, and VRF support.
- Configuration examples that highlight similarities and differences between NX-OS and IOS for EIGRP tasks like interface configuration, authentication, and summarization.
This document provides an overview of the network layer and some of its key protocols. It begins with an introduction to the network layer and its main responsibilities, including routing packets between subnets that may have different addressing schemes or protocols. It then discusses some of the network layer's main functionalities and features. The remainder of the document defines and describes several important network layer protocols, including EIGRP, ICMP, IGMP, IPv4, and others. It provides high-level explanations of how these protocols function and their roles within the network layer.
EIGRP is a proprietary routing protocol developed by Cisco that uses a composite metric and has fast convergence properties. It functions as a hybrid of distance-vector and link-state routing protocols, sending subnet mask and VLSM information in updates. EIGRP forms neighbor relationships through periodic hello messages and establishes three key tables - Neighbor, Topology, and Routing - to store neighbor, route, and best path information. It utilizes five packet types and reliable transport to efficiently share routing updates.
IGRP and EIGRP.
Comparison between traditional Distance Vector Routing Protocols and Enhanced Distance Vector Routing Protocols.
EIGRP Message Format and Packet Header.
EIGRP Parameters (K1,K2, K3, K4, K5, Reserved, and Hold Time).
Protocol Dependent Modules (PDM).
Reliable Transport Protocol (RTP).
EIGRP Packet Types (Hello Packets, Update packets, Acknowledgment packets, Query and Reply packets).
EIGRP Bounded Updates.
Introduction to DUAL Algorithm.
EIGRP Administrative Distance.
The router eigrp Command, the network command with a Wildcard Mask, Verifying EIGRP and using the Bandwidth command
EIGRP Metric Calculation, EIGRP uses Bandwidth, delay, reliability, and load in its metric.
DUAL Concepts, successor, Feasible distance (FD), Feasible successor (FS), Reported distance (RD)/ AD and Feasibility Condition (FC).
DUAL Finite State Machine, Null0 Summary Route, Disabling Automatic Summarization, Manual Summarization and EIGRP default route
EIGRP is an enhanced interior gateway routing protocol that has characteristics of both distance vector and link state routing. It supports features like classless routing, VLSM, route summarization, incremental updates, and load balancing. The maximum hop count for EIGRP is 224 and it uses the multicast address 224.0.0.10. EIGRP applies an administrative distance of 90 for internal routes and 170 for external routes.
- An autonomous system (AS) is a group of networks under single administrative control, each with a unique ID number. Interior gateway protocols (IGPs) like RIP, IGRP, EIGRP, OSPF route within an AS, while exterior gateway protocols like BGP route between ASes.
- IGRP is a distance vector protocol that uses a composite metric and broadcasts updates. EIGRP is an advanced hybrid protocol that uses multicast updates and three tables to store routing information. OSPF is a link-state protocol that forms adjacencies and uses areas and least-cost routing.
- Configuring these protocols involves enabling IP routing, specifying the routing protocol and associated networks, and verifying
Presentation about interior gateway routing protocol EIGRP which covers most of the concepts and features of the protocol.
Delivered by Dmitry Figol, CCIE R&S #53592.
The document provides an overview of the Border Gateway Protocol (BGP). It begins with general information about BGP, including that it is used for routing between autonomous systems and is classified as a path vector routing protocol. It then covers BGP theory in detail over several sections, explaining concepts like neighbors, messages, states, attributes and more. The document aims to provide thorough theoretical understanding needed to implement BGP in a lab.
EIGRP is an enhanced distance vector routing protocol developed by Cisco that provides faster convergence properties and lower usage of bandwidth compared to IGRP. EIGRP forms neighbor relationships to dynamically learn of route changes and failures. It uses the Diffusing Update Algorithm (DUAL) to select optimal routes and maintain three tables - the neighbor table, topology table, and routing table. EIGRP supports classless routing, variable length subnet masking, and multi-protocol routing. It provides rapid convergence, efficient bandwidth usage, and independence from routed protocols through features like partial route updates, hello packets, and protocol-dependent modules.
Packet Tracer: Routing protocols EIGRP and OSPFRafat Khandaker
The document summarizes an experiment in Packet Tracer where the routing protocols EIGRP and OSPF were implemented on a simulated enterprise network with multiple hosts and routers. EIGRP and OSPF were configured on the 3 routers to exchange routing update tables and allow routing between all hosts. The experiment demonstrated how each protocol operates, including configuration of EIGRP with autonomous system numbers and OSPF with areas to establish routing adjacencies between routers. Pings between hosts across the routers confirmed correct routing was achieved with both protocols.
This document provides an overview of the Enhanced Interior Gateway Routing Protocol (EIGRP). It describes the history and development of EIGRP, its basic operation and components, including reliable transport protocol, packet types, neighbor discovery via hello packets, and route updates using the diffusing update algorithm. It also covers basic EIGRP configuration such as enabling it with the router eigrp command, advertising networks, and verifying neighbor relationships.
Dynamic Routing All Algorithms, Working And BasicsHarsh Mehta
This document provides information on computer networks and routing protocols. It discusses advantages and problems of computer networks. It then describes the Enhanced Interior Gateway Routing Protocol (EIGRP) and some of its key features like security, congestion handling, efficiency, and support for IPv4 and IPv6. It also discusses static and dynamic routing, different routing metrics, and compares EIGRP to other routing protocols like RIP, OSPF, and IS-IS.
Route redistribution involves sharing routes between different routing protocols. Challenges include incompatible metrics between protocols and routing loops or suboptimal paths that can occur from redistributing routes back into their origin domain. Route maps, distribution lists, and adjusting administrative distances can control redistribution and prevent issues like feedback of routes into their source protocol.
Redistribution is necessary when routing protocols connect and must pass routes between the two.
Route Redistribution involves placing the routes learned from one routing domain, such as RIP, into
another routing domain, such as EIGRP.
While running a single routing protocol throughout your entire IP internetwork is desirable, multiprotocol routing is common for a number of reasons, such as company mergers, multiple departments
managed by multiple network administrators, and multi-vendor environments. Running different
routing protocols is often part of a network design.
Lecture number 5 Theory.pdf(machine learning)ZainabShahzad9
This document discusses computer networks and routing protocols. It provides an overview of key topics including:
- The difference between routed protocols like IPv4 and IPv6 that transfer user data, and routing protocols like RIP and OSPF that send route update packets.
- Common routing and routed protocols including IGPs, EGPs, RIP, OSPF, EIGRP and BGP.
- Desirable properties of routing algorithms such as correctness, robustness, stability, fairness and efficiency.
- Types of routing including fixed, flooding, dynamic and default routing. Characteristics of distance vector and link state routing protocols are also outlined.
Performance Analysis of Routing Protocols RIP, OSPF and EIGRPIRJET Journal
This document analyzes the performance of three routing protocols: RIP, OSPF, and EIGRP. It simulates these protocols using GNS3 software and analyzes parameters like convergence time, end-to-end delay, and throughput. Redistribution between the protocols is implemented using configuration commands. Ping tests and Wireshark analysis show packet forwarding between networks running different protocols. Analysis finds that EIGRP has the best performance with low convergence time and delay compared to RIP and OSPF in the simulated networks.
The document discusses various topics relating to EIGRP implementation including:
- Establishing EIGRP neighbor relationships and different network environments where EIGRP can operate like Frame Relay and MPLS networks.
- Building the EIGRP topology table by exchanging routing information with neighbors, calculating EIGRP metrics and selecting the best path.
- Optimizing EIGRP behavior such as using stub routing and route summarization to reduce queries when a route becomes active.
The document provides an overview of configuring the Enhanced Interior Gateway Routing Protocol (EIGRP). It describes the basic operation and components of EIGRP, including its tables, metrics, neighbor discovery, and packet types. The objectives are to describe EIGRP functionality, plan and implement EIGRP routing, and configure and verify EIGRP implementations in enterprise networks.
This chapter discusses the configuration of the Enhanced Interior Gateway Routing Protocol (EIGRP). It describes the basic operation and terminology of EIGRP, including its tables, metrics, and routing behavior. The chapter also covers EIGRP packet types, neighbor discovery, route calculation using the DUAL algorithm, and key technologies such as reliable transport and protocol-dependent modules. The overall purpose is to explain how to plan, implement, configure and verify EIGRP routing.
"IOS 18 CONTROL CENTRE REVAMP STREAMLINED IPHONE SHUTDOWN MADE EASIER"Emmanuel Onwumere
In iOS 18, Apple has introduced a significant revamp to the Control Centre, making it more intuitive and user-friendly. One of the standout features is a quicker and more accessible way to shut down your iPhone. This enhancement aims to streamline the user experience, allowing for faster access to essential functions. Discover how iOS 18's redesigned Control Centre can simplify your daily interactions with your iPhone, bringing convenience right at your fingertips.
3. What is EIGRP?
• EIGRP is an advanced distance-vector routing
protocol that relies on features commonly
associated with link-state protocols.
• EIGRP uses Link State's partial updates and
neighbor discovery.
• EIGRP's advanced features supports IP, IPX and
AppleTalk.
• EIGRP uses RTP (Reliable Transport Protocol) to
transport its routing updates
3
4. What Is EIGRP?
4
Enhanced
IGRP
IP Routing
Protocols
IPX Routing
Protocols
AppleTalk
Routing Protocol
IP Routing
Protocols
IPX Routing
Protocols
• Enhanced IGRP supports:
– Rapid convergence
– Reduced bandwidth usage
– Multiple network-layer support
• EIGRP includes support for AppleTalk, IP, and Novell NetWare as well
as IP and IP v.6. The AppleTalk implementation redistributes routes
learned from the Routing Table Maintenance Protocol (RTMP). The IP
implementation redistributes routes learned from OSPF, RIP, IS-IS, EGP
and BGP. The Novell implementation redistributes routes learned from
Novell RIP or Service Advertisement Protocol (SAP).
AppleTalk
Routing Protocol
5. What Is EIGRP?
• Enhanced IGRP supports:
– Uses Diffused Update Algorithm (DUAL) to select
loop-free routes and enable fast convergence.
• DUAL enables EIGRP routers to determine whether a path
advertised by a neighbor is looped or loop-free, and
• Allows a router running EIGRP to find alternate paths
without waiting on updates from other routers.
– Up to 6 unequal paths to remote network, default = 4
Enhanced
IGRP
IPX Routing
Protocols
AppleTalk
Routing Protocol
IP Routing
Protocols
IPX Routing
Protocols
AppleTalk
Routing Protocol
IP Routing
Protocols
5
6. Comparing EIGRP to IGRP
• Both IGRP and EIGRP:
– Use “Autonomous Systems” (AS) to divide the
internetwork
• [This is the number that you include when configuring the
protocol; e.g.: “router (e)igrp 1”
• All routers in the same AS
– use at least one common protocol,
– share the same routing information and
– are “contiguous”.
– They also use the same metrics: bandwidth, delay,
load and reliability; with MTU as a tiebreaker.
– Same load balancing properties
– Maximum hop count of 255 (100 default) 6
7. Comparing EIGRP to IGRP
• But EIGRP:
– Includes the subnet mask information in its routing
updates, which allows the use of VLSM.
– And helps EIGRP to differentiate between internal
(within an AS) and external (between ASs) routes
– Also, it does not send “any periodic updates” (which
IGRP sends every 90 seconds)
– EIGRP has improved convergence time – much
faster than IGRP
– EIGRP also sharply reduces network overhead
7
8. EIGRP for IP
• No updates: Route updates sent only when a change
occurs – multicast on 224.0.0.10
• “Hello” messages sent to neighbors every 5 seconds
(60 seconds in most WANs)
Enhanced IGRP
EIGRP EIGRP
hello
8
9. EIGRP for IP
EIGRP and PDMs (Protocol-dependent modules ):
– Supports IP (and through IP (v.4 & 6), IPX, OSPF, IS-IS,
RIP and RIP v.2, EGP (Exterior Gateway Protocol), and
BGP (Border Gate Protocol), AppleTalk which gives you
RTMP (Routing Table Maintenance Protocol), and Novell
NetWare, supporting IPX, Novell RIP and SAP (Service
Ad Protocol).
– EIGRP supports more protocols than any other routing
protocol, (only IS-IS comes close), by using PDMs.
– Each PDM keeps it’s own set of routing tables.
– PDMs are responsible for network layer protocol-
specific requirements.
• The IP-EIGRP module, for example, is responsible for sending
and receiving EIGRP packets that are encapsulated in IP. 9
10. EIGRP for IP
• EIGRP (other features):
– Is “Classless”
– Supports VLSM and CIDR.
– Supports “discontiguous” networks &
“summarization”
– Uses RTP (Reliable Transport Protocol) (see ff) for
communication – uses multicasts and unicasts for
quick updates with receipts for tracking data.
– Uses the “DUAL” algorithm; unique and efficient.
10
11. EIGRP Terminology and Operation 1
• EIGRP sends out five different types of packets—
– hello,
– update,
– query,
– reply, and
– acknowledge (ACK)—
• that establish the initial adjacency between neighbors
and to keep the topology and routing tables current.
• When troubleshooting an EIGRP network, network
administrators must understand what EIGRP packets are
used for and how they are exchanged.
• For example, if routers running EIGRP do not form
neighbor relationships, those routers cannot exchange
EIGRP updates with each other and cannot connect to
services across the internetwork. 11
12. • The following terms are related to EIGRP:
• Neighbor table (contains neighbors)
– EIGRP routers use hello packets to discover neighbors.
– When a router discovers and forms an adjacency with a new
neighbor, it includes the neighbor's address and the interface
through which it can be reached in an entry in the neighbor table.
– This table is comparable to the neighborship (adjacency)
database used by link-state routing protocols.
– It serves the same purpose—ensuring bidirectional
communication between each of the directly connected
neighbors.
– EIGRP keeps a neighbor table for each network protocol
supported; in other words, the following tables could exist: an IP
neighbor table, an IPX and an AppleTalk neighbor table. 12
EIGRP Terminology and Operation 2
13. • Topology table (contains updates re: all routes)
– When the router dynamically discovers a new
neighbor, it sends an update about the routes it knows
to its new neighbor and receives the same back.
– These updates populate the topology table.
– The topology table contains all destinations advertised
by neighboring routers;
• in other words, each router stores its neighbors' routing
tables in its EIGRP topology table.
– If a neighbor is advertising a destination, it must be
using that route to forward packets;
• this rule must be strictly followed by all distance vector
protocols.
• An EIGRP router maintains a topology table for each network
protocol configured (IP, IPX, and AppleTalk). 13
EIGRP Terminology and Operation 3
14. Advertised distance (AD) & feasible distance (FD)
– DUAL uses distance information, known as a metric or
cost, to select efficient, loop-free paths.
– The lowest-cost route is calculated by adding the cost
between the next-hop router and the destination—referred
to as the advertised distance—to the cost between the
local router and the next-hop router. The sum of these
costs is referred to as the feasible distance.
Successor
– Is a neighboring router that has a least-cost path to a
destination (the lowest FD) that is guaranteed not to be
part of a routing loop
– Successors are used for forwarding packets.
– Multiple successors can exist if they have the same FD.
14
EIGRP Terminology and Operation 4
15. • Routing table (contains only the best routes)
– Holds the best routes to each destination and is
used for forwarding packets.
– Successor routes are offered to the routing table.
– If a router learns more than one route to exactly the
same destination from different routing sources, it
uses the administrative distance to determine which
route to keep in the routing table.
– By default, up to 4 routes to the same destination
with the same metric can be added to the routing
table (the table can hold up to 6 unequal cost paths).
– The router maintains one routing table for each
network protocol configured. 15
EIGRP Terminology and Operation 5
16. • Feasible successor (FS)
– Along with keeping least-cost paths, DUAL keeps
backup paths to each destination.
– The next-hop router for a backup path is called the
“feasible successor”.
– To qualify as a feasible successor, a next-hop router
must have an AD less than the FD of the current
successor route
• in other words, a feasible successor is a neighbor that is
closer to the destination, but it is not the least-cost path
and, thus, is not used to forward data.
• Feasible successors are selected at the same time as
successors but are kept only in the topology table.
• The topology table can maintain multiple feasible
successors for a destination.
16
EIGRP Terminology and Operation 6
17. – If the route via the successor becomes invalid
(because of a topology change for example) or if a
neighbor changes the metric, DUAL checks for
feasible successors to the destination.
– If a feasible successor is found, DUAL uses it, thereby
avoiding recomputing the route.
– If no suitable feasible successor exists, a
recomputation must occur to determine the new
successor.
– Although recomputation is not processor-intensive, it
does affect convergence time, so it is advantageous to
avoid unnecessary recomputations.
17
EIGRP Terminology and Operation 7
18. IGRP and EIGRP Metric Calculation - 1
• The composite metric is calculated with the
following formula:
• By default, k1=k3=1 and k2=k4=k5=0. The default
composite metric for EIGRP, adjusted for scaling
factors, is as follows:
18
19. • BWmin is in kbps and the sum of delays are in 10s of
microseconds.
• Example
• The bandwidth and delay for an Ethernet interface are 10
Mbps and 1ms, respectively.
• The calculated EIGRP BW metric is as follows:
– 256 × 107/BW = 256 × 107/10,000,
– = 256 x (10,000,000/10,000)
– = 256 × 10,000
– = 256000
19
IGRP and EIGRP Metric Calculation - 2
20. EIGRP Neighbor Discovery -1
• EIGRP routers actively establish relationships with their
neighbors, similar to what Link State routers do.
• EIGRP routers establish “adjacencies” with neighbor routers
by using small hello packets.
• The Hello protocol uses a multicast address of 224.0.0.10,
and all routers periodically send hellos.
20
21. EIGRP Neighbor Discovery - 2
• On hearing hellos, the router creates a table of its
neighbors.
• The continued receipt of these packets maintains the
neighbor table
• To become a neighbor, the following 3 conditions must
be met:
1. The router must hear a hello packet or an ACK from a
neighbor.
2. The AS number in the packet header must be the same as
that of the receiving router.
3. The neighbor’s metric settings must be the same.
• Note:
– Each Layer 3 protocol has its own neighbor table.
21
23. Neighbor Discovery - 4
By forming adjacencies, EIGRP routers do the
following:
– Dynamically learn of new routes that join their
network
– Identify routers that become either unreachable or
inoperable
– Rediscover routers that had previously been
unreachable
23
24. EIGRP Timers
• EIGRP updates are set only when necessary and are
sent only to neighboring routers. There is no periodic
update timer.
• EIGRP use hello packets to learn of neighboring routes.
• The holdtime to maintain a neighbor adjacency is three
times the hello time.
• For hello is not received with the holdtime, the
neighbor is removed from the table.
24
26. Routing Concepts
– Topics now considered in more detail:
• EIGRP relies on four fundamental concepts:
1. neighbor tables,
2. topology tables,
3. route states, and
4. route tagging.
• Each of these is summarized in the slides that
follow.
26
27. Routing Concepts: 1. Neighbor Tables
• One neighbor table exists
for each protocol-
dependent module.
When a router discovers a new
neighbor, it records the
neighbor’s address and
interface as an entry in the
“neighbor table”.
• This is the amount of time
that a router treats a
neighbor as reachable and
operational.
When a neighbor sends a hello
packet, it advertises a hold time.
• DUAL is informed of the
topology change.
If a hello packet is not received
within the hold time, the hold
time expires.
27
28. Routing Concepts: 1. Neighbor Tables
A neighbor-table entry includes info
required by RTP.
Sequence numbers are employed to match
acknowledgments with data packets, and the
last sequence number received from the
neighbor is recorded so that out-of-order
packets can be detected.
A “transmission list” is used to queue packets for
possible retransmission on a per-neighbor basis.
“Round-trip timers” are kept in the neighbor-table
entry to estimate an optimal retransmission interval.
28
29. What is in the Neighbor Table?
SRTT: “Smooth Round Trip timer”: Time
for round trip to neighbor and back.
RTO: “Retransmission Time Out”: Time
EIGRP waits to send a packet from its
retransmission queue to a neighbor.
Q count - the number of EIGRP Packets
that the software is waiting to send 29
30. Routing Concepts: 2. Topology Tables
The “topology table” contains all destinations advertised by
neighboring routers.
The protocol-dependent modules populate the table, and the table
is acted on by the DUAL “finite-state” machine.
Each entry in the topology table includes the destination address
and a list of neighbors that have advertised the destination.
For each neighbor, the entry records the advertised metric, which
the neighbor stores in its routing table.
An important rule that distance vector protocols must follow is that if
the neighbor advertises this destination, it must use the route to
forward packets. 30
31. Dual Terminology - 1
• AD (Advertised distance) is the metric that is reported
by the neighbor router(s).
• FD (Feasible Distance) – Feasible distance is the metric
that is reported by neighbor router(s), plus the cost
associated with the forwarding link from the local
interface to the neighbor router(s).
– When multiple paths exist, the “local FD” is the lowest-cost
metric to a remote network.
• Feasibility Condition – If the AD from a given neighbor
is less than the locally calculated FD, that neighbor
meets the criteria to become the feasible successor.
31
32. Dual Terminology - 2
• Successor - A successor is a neighboring router that
is currently being used for packet forwarding; it
provides the least-cost route to the destination and is
not part of a routing loop
• Feasible successor - A feasible successor is a backup
route. Feasible successors provide the next lowest-cost
path without introducing routing loops.
– Feasible successor routes can be used in case the existing
route fails.
– Packets to the destination network are immediately
forwarded to the feasible successor, which at that point is
promoted to the status of successor
32
33. Successor routes
• Successor route is used by EIGRP to forward traffic to a
destination
• A successor routes may be backed up by a feasible successor
route
• Successor routes are stored in both the topology table and the
routing table
Routing Table—IP
Destination 1 Successor
Topology Table—IP
Destination 1 Successor
Destination 1 Feasible Successor
33
38. Dual Example – 1b
• In the previous slide, EIGRP's composite metric is replaced
by a link cost to simplify calculations.
• RTA's topology table includes a list of all routes advertised
by neighbors.
• For each network, RTA keeps the real (computed) cost of
getting to that network and also keeps the advertised cost
(reported distance) from its neighbor.
38
39. Dual Example – 1c
• RTY is the successor to network 24, by virtue of its
lowest computed cost 31. This value is also the FD to
Network 24.
• RTA follows a three-step process to select a feasible
successor to become a successor for Network 24:
– Determine which neighbors have a reported distance (RD)
(=AD) to Network 24 that is less than 31.
– RTX's RD is 30 < 31, meet FC and is a feasible successor.
– RTZ's RD is 220 > 31, not meet FC, and cannot be a FS.
39
41. Dual Example – 2b
• In this example, (a) is the destination network,
• From C’s point of view, if it goes to (a) via B, the
FD is 3 and the AD is 1. Others entries are
computed in the same manner.
• Note in the example that router D does not
have a feasible successor identified. The FD
for router D to router A is 2 and the AD via router
C is 3. Because the AD is larger than the FD,
no feasible successor is placed in the topology
table.
41
42. Dual Example – 2c
• Router C has a feasible successor identified
because the AD for the next hop router is
less than the FD for the successor.
• How about router E?
42
43. EIGRP Convergence - 1
• In the context of routing protocols, convergence
refers to the speed and ability of a group of
internetworking devices running a specific routing
protocol to agree on the topology of an internetwork
after a change in that topology.
• DUAL results in EIGRP's exceptionally fast
convergence. Why?
• The FS provides the capability to make an immediate
switchover to a backup route!
43
45. EIGRP Neighbor Tables
• The most important table in EIGRP is the neighbor table and
relationships tracked in the neighbor table are the basis for all
the EIGRP routing update and convergence activity.
• The neighbor table contains information about adjacent
neighboring EIGRP routers.
• A neighbor table is used to support reliable, sequenced
delivery of packets.
• An EIGRP router can maintain neighbor tables, one for each
PDM running (e.gmultiple ., IP, IPX, and AppleTalk) routed
protocols.
45
46. EIGRP Packet Types - 1
• Hello packets assist in the discovery of EIGRP
neighbors.
– The packets are multicast to 224.0.0.10.
• An acknowledgment packet acknowledges the
reception of an update packet.
– An acknowledgment packet is a hello packet with no data.
– Acknowledgment packets are sent to the unicast address of
the sender of the update packet.
46
47. EIGRP Packet Types - 2
• Update packets contain the routing information of
destinations.
– Update packets are unicast to newly discovered neighbors;
otherwise, update packets are multicast to 224.0.0.10 when a
link metric changes.
– Update packets are acknowledged to ensure reliable
transmission.
• Query packets are sent to find feasible successors to
a destination.
– Query packets are always multicast.
47
48. EIGRP Packet Types - 3
• Reply packets are sent to respond to query
packets.
– Reply packets provide a feasible successor to the
sender of the query.
– Reply packets are unicast to the sender of the query
packet.
48
49. Routing Concepts: 3. Route States
A topology-table entry for a destination can exist in one of two states:
active or passive.
A destination is in the passive state when the router is not performing
a recomputation; it is in the active state when the router is.
If feasible successors are always available, a destination never has
to go into the active state, thereby avoiding a recomputation.
A recomputation occurs when a destination has no feasible
successors.
The router initiates the recomputation by sending a query packet to
each of its neighboring routers.
After the router has received a reply from each neighboring router the
router can select a successor.
49
50. Routing Concepts: 4. Route Tagging
EIGRP supports internal
and external routes.
Internal routes originate
within an EIGRP AS.
External routes are
learned by another
routing protocol or
reside in the routing
table as static routes.
These routes are tagged
individually with the
identity of their origin.
External routes are tagged with this
information:
• Router ID of the router that redistributed the
route
• AS number of the destination
• Configurable administrator tag
• ID of the external protocol
• Metric from the external protocol
• Bit flags for default routing
50
51. EIGRP Tables and Packets
• The neighbor table and topology table are held in
ram and are maintained through the use of hello
and update packets.
Enhanced IGRP
EIGRP EIGRP
hello
To see all feasible successor routes known to a router, use the
“show ip eigrp topology” command
51
52. Choosing Routes
• EIGRP uses a composite metric to pick the best path:
bandwidth and delay of the line by default.
• EIGRP can load balance across six unequal cost paths to
a remote network (4 by default)
IPX
19.2
T1
T1 T1
IPX
AppleTalk
IP
AppleTalk
IP
A B
D
C
52
53. Configuring EIGRP for IP
172.16.10.0
10.110.1.0
192.168.0.0
Token
Ring
AS=10
Router(config)#router eigrp 10
Router(config-router)#network 10.0.0.0
Router(config-router)#network 172.16.0.0
192.168.0.0
A C
B
Enable EIGRP
Assign networks
If you use the same AS number for EIGRP as IGRP, EIGRP will automatically
redistribute IGRP into EIGRP
53
54. Redistribution
Redistribution is translating one type of routing
protocol into another.
Router D
Router B
Router A
Router C
EIGRP IGRP
IGRP and EIGRP translate automatically, as long as they are both using the
same AS number. See another example - next slide:
54
56. Route Path
Assuming all default parameters, which route will
RIP (v1 and v2) take, and which route(s) will
IGRP and EIGRP take to get from Routers A to B?
T1 T1
100BaseT
100BaseT
10BaseT
56K
56
Router A Router B
57. Verifying EIGRP Operation
• Displays the neighbors discovered
by IP Enhanced IGRP
• Displays the IP Enhanced IGRP
topology table
• Displays current Enhanced IGRP
entries in the routing table
• Displays the parameters and current
state of the active routing protocol
process
• Displays the number of IP Enhanced
IGRP packets sent and received
show ip protocols
Router#
show ip route eigrp
Router#
show ip eigrp traffic
Router#
show ip eigrp neighbors
Router#
show ip eigrp topology
Router#
57
58. Show IP Route
-D is for “DUAL”
-[90/2172] is the administrative distance and cost of
the route. The “cost” of the route is a composite metric
comprised from the bandwidth and delay of the line
P1R1#sh ip route
[output cut]
Gateway of last resort is not set
D 192.168.30.0/24 [90/2172] via 192.168.20.2,00:04:36, Serial0/0
C 192.168.10.0/24 is directly connected, FastEthernet0/0
D 192.168.40.0/24 [90/2681] via 192.168.20.2,00:04:36, Serial0/0
C 192.168.20.0/24 is directly connected, Serial0/0
D 192.168.50.0/24 [90/2707] via 192.168.20.2,00:04:35, Serial0/0
P1R1#
58
59. Some EIGRP Features
• Large Network support:
– Support for multiple Autonomous Systems: This is
one way to break up a large number of hosts.
• VLSM Support and Summarization:
– Support for “discontiguous networks”:
– This is a network in which 2 subnets of a classful
network; say, 10.1.0.0 and 10.2.0.0, which are both
part of the “classful” 10.0.0.0 network,
– are separated by a different classful network; say
172.16.0.0, or any subnet in that network.
– By default, EIGRP does not handle this configuration,
(only OSPF can), but it can be configured to do so. 59
60. Some EIGRP Features
• Load Balancing:
– EIGRP can handle equal or unequal load balancing
– By default, up to 4 links; up to 6 links can be
configured with the “maximum paths” command.
60
61. EIGRP Configuration
• Initial Setup (pg 426, and Cisco command reference):
• Step Command Purpose
• 1 router eigrp autonomous-system Enable an EIGRP routing
process in global config mode.
• 2 network network-number Associate networks with an EIGRP
routing process in router config mode.
• Create a Passive Interface This prohibits an interface from sending or
– Router(config-router)#passive-interface serial 0/1 receiving Hellos; so it will never form
adjacencies.
• Redistribution and Set Metric values
– The following example takes redistributed Routing Information Protocol (RIP) metrics and
translates them into EIGRP metrics with values as follows: bandwidth = 1000, delay = 100,
reliability = 250, loading = 100, and MTU = 1500.
– router eigrp 1
– network 172.16.0.0 Command Syntax
– redistribute rip redistribute (IP)
– default-metric 1000 100 250 100 1500 default-metric bandwidth delay reliability loading mtu
61
62. EIGRP Configuration (continued)
Load Balancing –
– This is automatic with EIGRP; the only time you need to configure
it is when you want to vary the load over each of several links.
– In this case you would use the “traffice-share balanced” or the
“variance” command:
• To control how traffic is distributed among routes when there are multiple
routes for the same destination network that have different costs, use the
traffic-share balanced command in router configuration mode. To disable
this function, use the no form of the command.
– traffic-share balanced
• To control load balancing in an Enhanced Interior Gateway
Routing Protocol (EIGRP) based internetwork, use the
variance command in router configuration mode. To reset
the variance to the default value, use the no form of this
command.
– variance multiplier 62
63. •Open standard
•Shortest path first (SPF) algorithm
•Link-state routing protocol (vs. distance vector)
•Can be used to route between AS’s
Introducing OSPF (pg 444 ff)
64. OSPF Hierarchical Routing
• Consists of areas and autonomous systems
• Minimizes routing update traffic
• Supports VLSM
• Unlimited hop count
64
65. Link State Vs. Distance Vector
Link State:
• Provides common view of entire topology
• Calculates shortest path
• Utilizes event-triggered updates
• Can be used to route between AS’s
Distance Vector:
•Exchanges routing tables with neighbors
•Utilizes frequent periodic updates
65
66. Types of OSPF Routers
Internal
Routers
Area 1 Area 2
ASBR and
Backbone
Router
Backbone/
Internal
Routers
ABR and
Backbone
Router
Backbone Area 0
ABR and
Backbone
Router
Internal
Routers
•External AS
66
67. Compare RIP to OSPF
67
Feature RIP OSPF
Algorithm Vector-distance Link-state
Maximum Hops
15 hops. 16 hops is considered
to be infinity, implying that the
destination is unreachable
Limited only by size of routing tables within
routers
Subsystem
Segmentation
Treats the autonomous system
as a single subsystem
Breaks the autonomous system into one or
more areas with two levels of routing
algorithms, intra-area, and inter-area.
Metric Destination/hop Destination/cost/link identifier
Integrity
No authentication in RIP-1,
Authentication has been added
to RIP-2
Supports Authentication. Several
authentication algorithms are available
ranging from simple password operations to
more complex cryptographic algorithms.
Complexity Relatively Simple
More Complex. Several more PDUs and
exchanges are defined in the protocol.
Routing tables are large and include not
only destinations, but also a tree
representation of local network.
Acceptance
Widely Available, BSD routed
supports RIP
Newer, published in RFCs
Route Options
Identifies a single route to a
destination
Supports multiple routes to a single
destination. Facilitates load-balancing traffic
distribution
Types of Routes
Host, network. RIP-2 adds the
ability to transfer subnetwork
route entries
Host, network, and subnetwork routes
68. Router(config-router)#network address mask area <area-id>
Assigns networks to a specific OSPF area
Router(config)#router ospf <process-id>
Defines OSPF as the IP routing protocol.
Note: The process ID is locally significant and is needed
to identify a unique instance of an OSPF database
Configuring Single Area OSPF
69. OSPF Example
hostname R3
router ospf 10
network 10.1.2.3 0.0.0.0 area 0
network 10.1.3.1 0.0.0.0 area 0
hostname R2
router ospf 20
network 10.0.0.0 0.255.255.255 area 0
hostname R1
router ospf 30
network 10.1.0.0 0.0.255.255 area 0
network 10.5.5.0 0.0.0.0 area 0
R3
R2
R1
10.1.2.0 10.1.1.0
10.5.5.0
Area 0
10.1.3.0
69
70. Router#show ip ospf interface
Verifying the OSPF Configuration
Displays area-ID and adjacency information
Router#show ip protocols
Verifies that OSPF is configured
Router#show ip route
Displays all the routes learned by the router
Router#show ip ospf neighbor
Displays OSPF-neighbor information on a per-interface basis
70
71. OSFP Neighbors
• OSPF uses hello packets to create adjacencies and
maintain connectivity with neighbor routers
• OSPF uses the multicast address 224.0.0.5
Hello?
224.0.0.5
•Hello packets provides dynamic neighbor discovery
•Hello Packets maintains neighbor relationships
•Hello packets and LSA’s from other routers help build & maintain the topological database
71
72. OSPF Terminology
Neighbor:
– Two routers that have an interface on a common network
– Usually discovered by hello’s but can also be configured administratively
Adjacency
– Relationship formed between selected neighbors in which routing
information is exchanged. Not all neighbors are adjacent
– Only Broadcast and Non-Broadcast network types have Designated
and Backup Designated Routers!!!
Neighbors
Cost=6
ABR
BDR
DR
Non-DR
Adjacencies
72
73. OSPF Terminology – Table: part 1
73
Term Description
Link state
Information is shared between directly connected routers. This information propagates throughout the
network unchanged and is also used to create a shortest path first (SPF) tree.
Area A group of routers that share the same area ID. All OSPF routers require area assignments.
Autonomous system (AS) A network under a common network administration.
Cost
The routing metric used by OSPF. Lower costs are always preferred. You can manually configure the
cost with the ip ospf cost command. By default, the cost is calculated by using the formula cost = 108
/
bandwidth.
Router ID
Each OSPF router requires a unique router ID, which is the highest IP address configured on a Cisco
router or the highest numbered loopback address. You can manually assign the router ID.
Adjacency
When two OSPF routers have exchanged information between each other and have the same topology
table. An adjacency can have the following different states or exchange states:
1. Init state —When Hello packets have been sent and are awaiting a reply to establish two-way communication.
2. Establish bi-directional (two-way) communication —Accomplished by the discovery of the Hello protocol routers and the election
of a DR.
3. Exstart —Two neighbor routers form a master/slave relationship and agree upon a starting sequence to be incremented to ensure
LSAs are acknowledged.
4. Exchange state —Database Description (DD) packets continue to flow as the slave router acknowledges the master's packets.
OSPF is operational because the routers can send and receive LSAs between each other. DD packets contain information, such as
the router ID, area ID, checksum, if authentication is used, link-state type, and the advertising router. LSA packets contain
information, such as router ID also but in addition include MTU sizes, DD sequence numbering, and any options.
5. Loading state —Link-state requests are sent to neighbors asking for recent advertisements that have not yet been discovered.
6. Full state —Neighbor routers are fully adjacent because their link-state databases are fully synchronized. Routing tables begin to
be populated.
74. OSPF Terminology – Table: part 2
74
Topology table Also called the link-state table. This table contains every link in the whole network.
Designated router (DR)
This router is responsible for ensuring adjacencies between all neighbors on a
multiaccess network (such as Ethernet). This ensures all routers do not need to
maintain full adjacencies with each other.
The DR is selected based on the router priority. In a tie, the router with the highest router ID is selected.
Backup DR A backup router designed to perform the same functions in case the DR fails.
Link-state advertisement
(LSA)
A packet that contains all relevant information regarding a router's links and the
state of those links.
Priority Sets the router's priority so a DR or BDR can be correctly elected.
Router links
Describe the state and cost of the router's interfaces to the area. Router links use
LSA type 1.
Summary links
Originated by area border routers (ABRs) and describe networks in the AS.
Summary links use LSA types 3 and 4.
Network links Originated by DRs. Network links use LSA type 2.
External links
Originated by autonomous system boundary routers (ASBRs) and describe
external or default routes to the outside (that is, non- OSPF) devices for use with
redistribution. External Links use the LSA type 5.
Area border router (ABR)
Router located on the border of one or more OSPF areas that connects those areas
to the backbone network.
Autonomous system
75. Router ID (RID)
Each router in OSPF needs to be uniquely identified to
properly arrange them in the Neighbor tables.
75
76. Electing the DR and BDR
• OSPF sends Hellos which elect DRs and BDRs
• Routers form adjacencies with DRs and BDRs in a multi-access
environment
• The next slide covers loopback interfaces. The reason you would
configure a loopback (a logical interface) is to assign it the highest
priority interface on the router, thus ensuring that it will become the
DR.
• This avoids the router selecting a physical interface as DR, which is
sometimes undesirable because physical interfaces can go up and
down and sometimes fail to provide a stable routing environment.
Multicast Hellos are sent and compared
Router with Highest Priority is Elected as DR
Router with 2nd Highest Priority is Elected as BDR
76
77. Configuring Loopback Interfaces
Router ID (RID):
– Number by which the router is known to OSPF
– Default: The highest IP address on an active interface at the
moment of OSPF process startup
– Can be overridden by a loopback interface: Highest IP address
of any active loopback interface – also called a logical interface
78. Interface Priorities
What is the default OSPF interface priority?
Router# show ip ospf interface ethernet0/0
Ethernet0 is up, line protocol is up
Internet Address 192.168.1.137/29, Area 4
Process ID 19, Router ID 192.168.1.137, Network Type BROADCAST,
Cost: 10 Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 192.168.1.137, Interface address 192.168.1.137
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 0, maximum is 0
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
78
79. ip ospf priority
• To set the router priority, which helps determine the designated
router for this network, use the ip ospf priority command in
interface configuration mode.
– To return to the default value, use the no form of this command.
• ip ospf priority number-value
• no ip ospf priority number-value
• Syntax Description
– number-value <A number value that specifies the priority of
the router. The range is from 0 to 255>
79
Interface Priorities
80. Ensuring your DR
What options can you configure that will ensure that R2 will be
the DR of the LAN segment?
81. Configuring Wildcards
If you want to advertise a partial octet (subnet),
you need to use wildcards.
– 0.0.0.0 means all octets match exactly
– 0.0.0.255 means that the first three match exactly,
but the last octet can be any value
After that, you must remember your block sizes….
81
82. Wildcard
The wildcard address is always one less than the block
size….
– 192.168.10.8/30 = 0.0.0.3
– 192.168.10.48/28 = 0.0.0.15
– 192.168.10.96/27 = 0.0.0.31
– 192.168.10.128/26 = 0.0.0.63
– What the author means is that where, in the first line, you’ve
borrowed 6 bits to get a /30 subnet mask, and this would give
you 64 subnets with 4 hosts in each! The “4” is the “block size”
that the author refers to. So, in the wildcard, the last number
must be one less than 4, or “3”.
– Same thing in line 2: /28 means 4 bits borrowed; this gives you
16 subnets with 16 hosts in each. Block size is 16 and the
wildcard is 16-1, or 15.
82