Routing Protocols and Concepts: Chapter 3 docx

Chapter 9
EIGRP
2
For further information
 This presentation is an
overview of what is
covered in the
curriculum/book.
 For further explanation
and details, please read
the chapter/curriculum.
 Book:
 Routing Protocols
and Concepts
 By Rick Graziani and
Allan Johnson
 ISBN: 1-58713-206-0
 ISBN-13: 978-58713-
206-3
3
Topics
 Introduction to EIGRP
 EIGRP: An Enhanced Distance
Vector Routing Protocol
 EIGRP Message Format
 Protocol-Dependent Modules
 RTP and EIGRP Packet Types
 Hello Protocol
 EIGRP Bounded Updates
 DUAL: An Introduction
 Administrative Distance

 Authentication
 Basic EIGRP Configuration
 EIGRP Network Topology
 Autonomous Systems and
Process IDs
 The router eigrp Command
 The network Command
 Verifying EIGRP
 Examining the Routing Table
 EIGRP Metric Calculation
 EIGRP Composite Metric and the K
Values
 EIGRP Metrics
 Using the bandwidth Command
 Calculating the EIGRP Metric
 DUAL
 DUAL Concepts
 Successor and Feasible Distance
 Feasible Successors, Feasibility
Condition, and Reported Distance
 Topology Table: Successor and
Feasible Successor
 Topology Table: No Feasible
Successor
 Finite State Machine
 More EIGRP Configurations
 The Null0 Summary Route
 Disabling Automatic Summarization
 Manual Summarization
 EIGRP Default Route

 Fine-Tuning EIGRP
Introduction to EIGRP
 EIGRP: An Enhanced Distance Vector Routing Protocol
 EIGRP Message Format
 Protocol-Dependent Modules
 RTP and EIGRP Packet Types
 Hello Protocol
 EIGRP Bounded Updates
 DUAL: An Introduction
 Administrative Distance
 Authentication
5
Introduction to EIGRP
 Enhanced Interior Gateway Routing Protocol (EIGRP)
 Distance vector
 Classless routing protocol
 Released in 1992 with Cisco IOS Software Release 9.21.
 Enhancement of Cisco Interior Gateway Routing Protocol (IGRP).
 Both are Cisco proprietary
 Operate only on Cisco routers.
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Introduction to EIGRP
 The term hybrid routing protocol is sometimes used to define
EIGRP.
 Misleading, not a hybrid between distance vector and link-state
 Solely a distance vector routing protocol.
7
Introduction to EIGRP
 Instead of hop count, both IGRP and EIGRP use metrics composed
of bandwidth, delay, reliability, and load.

 Only bandwidth and delay are used by default.
8
EIGRP Message Format
 EIGRP Header field
 Data field = Type/Length/Value, or TLV.
 Encapsulated in an IP packet.
 Protocol field = 88 (EIGRP)
 Destination IP address = multicast 224.0.0.10.
 If the EIGRP packet is encapsulated in an Ethernet frame:
 Destination MAC, multicast address: 01-00-5E-00-00-0A
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EIGRP Message Format
 Opcode specifies the EIGRP packet type as one of the following:
 Update
 Query
 Reply
 Hello
Note: All fields are shown to
provide an accurate picture
of the EIGRP message
format. However, only the
fields relevant to the CCNA
candidate are discussed.
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EIGRP Packet Header Message Format
 Autonomous system number
 Specifies the EIGRP routing process.
 Unlike RIP, Cisco routers can run multiple instances of EIGRP.
(more later)
 EIGRP packet types are discussed later in this chapter.

Note: All fields are shown to
provide an accurate picture
of the EIGRP message
format. However, only the
fields relevant to the CCNA
candidate are discussed.
11
EIGRP TLV Message Format
 EIGRP uses weights for its composite metric.
 Default, only bandwidth (K1) and delay (K3) are weighted (used)
 Set to 1.
 Other K values are set to 0 (affect load and reliability).
 More later.
 The hold time
 Amount of time the EIGRP neighbor receiving this message should wait
before considering the advertising router to be down.
 More later
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IP Internal
Routes TLV
 Metric fields:
 Delay and Bandwidth
 Reliability and Load
 (more later)
 Subnet mask field (Prefix Length):
 Example, the prefix length for 255.255.255.0 is 24 (/24)
 Destination field:
 The destination network.
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IP External

Routes TLV
 In this chapter, we import or redistribute a default static route into
EIGRP.
 Additional fields
 All the fields used by the IP Internal TLV
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Note on MTU
 Some EIGRP literature might incorrectly state that the maximum
transmission unit (MTU) is one of the metrics used by EIGRP.
 MTU is not a metric used by EIGRP.
 The MTU is included in the routing updates, but it is not used to
determine the routing metric.
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Protocol-
Dependent
Modules
 EIGRP uses protocol-dependent modules (PDM). to route different
protocols, including:
 IP, Internetwork Packet Exchange (IPX)
 AppleTalk,
 PDMs are responsible for the specific routing tasks for each network layer
protocol.
 Example The IP-EIGRP module is responsible for:
 Sending and receiving EIGRP packets that are encapsulated in IP.
 Using DUAL to build and maintain the IP routing table.
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RTP and EIGRP Packet Types
 Reliable Transport Protocol (RTP)
 Delivery and reception of EIGRP packets.
 Cannot use the services of UDP or TCP

 IPX and AppleTalk do not use protocols from the TCP/IP protocol suite.
 RTP includes both reliable delivery and unreliable delivery of EIGRP
packets:
 Reliable RTP requires an acknowledgment (like TCP).
 Unreliable RTP does not require an acknowledgment (like UDP).
 RTP can send packets either as a unicast or a multicast (224.0.0.10).
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EIGRP Packet
Types –
Hello
Packet
 Hello packets are used by EIGRP to:
 Discover neighbors
 Form adjacencies with those neighbors
 EIGRP hello packets:
 multicasts
 unreliable delivery
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 Update Packets
 Contains only the routing information needed (a change occurs)
 Sent only to those routers that require it.
 Uses reliable delivery.
 Multicast when sent to multiple routers
 Unicast when sent to a single router
 Acknowledgment (ACK) Packets
 Sent when reliable delivery is used (update, query, and reply
packets).
 Sent as an unreliable unicast.
EIGRP Packet
Types –

Update and
Acknowledgement
Packets
X
EIGRP uses
triggered
updates
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EIGRP Packet
Types – Query
and Reply
Packets
 Used by DUAL when searching for networks and other tasks.
 Queries and replies use reliable delivery.
 To keep this example simple, acknowledgments were omitted in the
graphic.
 All neighbors must send a reply regardless of whether they have a route
to the downed network.
 Queries can use multicast or unicast, whereas replies are always sent as
unicast.
 DUAL is discussed in a later section.
 Queries and replies packets are discussed in more detail in CCNP.
X
Why Query? Another
router could be
attached to the same
LAN.
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Hello Protocol
 Before any EIGRP packets can be exchanged between routers,

EIGRP must first discover its neighbors.
 EIGRP routers discover neighbors and establish adjacencies with
neighbor routers using the hello packet.
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Hello Protocol
 Most networks, EIGRP hello packets are sent every 5 seconds.
 On multipoint nonbroadcast multiaccess (NBMA) networks such as
X.25, Frame Relay, and ATM interfaces with access links of T1 (1.544
Mbps) or slower, hellos are unicast every 60 seconds.
 An EIGRP router assumes that as long as it is receiving hello packets from
a neighbor, the neighbor and its routes remain viable.
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Hello Protocol
 Hold time - maximum time the router should wait to receive the
next hello before declaring that neighbor as unreachable.
 Default hold time - 3 times the hello interval,
 15 seconds on most networks
 180 seconds on low-speed NBMA networks
 If the hold time expires:
 EIGRP declares the route as down
 DUAL searches for a new path in the topology table or by
sending out queries.
 More later.
23
EIGRP Bounded
Updates
 EIGRP uses the terms partial and bounded when referring to its
update packets.
 EIGRP sends its updates only when the metric for a route changes.
 The term partial means that the update only includes information

about the route changes.
 The term bounded refers to the propagation of partial updates
sent only to those routers that are affected by the change.
 This minimizes the bandwidth required to send EIGRP packets.
24
DUAL: An Introduction
 Diffusing Update Algorithm (DUAL) is the convergence algorithm used by
EIGRP.
 First proposed by E. W. Dijkstra and C. S. Scholten.
 The most prominent work with DUAL has been done by J. J. Garcia-Luna-
Aceves.
 Routing loops, even temporary ones, can be extremely detrimental to
network performance.
 Distance vector routing protocols such as RIP prevent routing loops with
hold-down timers and split horizon.
 Although EIGRP uses both of these techniques, it uses them somewhat
differently; the primary way that EIGRP prevents routing loops is with the
DUAL algorithm.
J. J. Garcia-Luna-Aceves
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DUAL: An Introduction
1. A directly connected network on R2 goes down.
 R2 sends an EIGRP update message to its neighbors indicating
the network is down .
2. R1 and R3 return an EIGRP acknowledgment indicating that they
have received the update from R2.
X X