EIGRPRouting Protocols and Concepts – Chapter 9

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Developed in 1985 to overcome RIPv1’s limited hop count -Distance vector routing protocol -Metrics used b IGRP M ti d by bandwidth (used by default) Delay (used by default) Reliability (not used by default) Load (not used by default) -Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S

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EIGRP Routing Protocols and Concepts – Chapter 9 ITE PC v4.0 1 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Introduction Introduction ITE PC v4.0 2 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP Roots of EIGRP: IGRP -Developed in 1985 to overcome RIPv1’s limited hop count -Distance vector routing protocol -Metrics used by IGRP IGRP bandwidth (used by default) Delay (used by default) (used by default) Reliability (not used by default) Load (not used by default) Load (not used by default) -Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S ITE PC v4.0 3 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP is a distance vector, classless routing protocol that was released in 1992 with IOS released in 1992 with IOS 9.21. As its name suggests, EIGRP is an enhancement of Cisco IGRP (Interior Gateway Routing Protocol). Both are Cisco proprietary protocols and only operate on Cisco Both are Cisco proprietary protocols and only operate on Cisco routers. The main purpose in Cisco's development of EIGRP was to create a classless version of IGRP. EIGRP includes several features that are not commonly found in other distance vector features that are not commonly found in other distance vector routing protocols like RIP (RIPv1 and RIPv2) and IGRP. These features include: –Reliable Transport Protocol (RTP) –Bounded Updates –Diffusing Update Algorithm (DUAL) –Establishing Adjacencies –Neighbor and Topology Tables Alth Although EIGRP may act like a link-state routing protocol, it is EIGRP lik li it still a distance vector routing protocol. –Note: The term hybrid routing protocol is sometimes used to define EIGRP. However, this term is misleading because EIGRP is not a hybrid between distance vector and link hybrid between distance vector and link-state routing protocols - it is routing protocols it is solely a distance vector routing protocol. Therefore, Cisco is no longer using this term to refer to EIGRP. ITE PC v4.0 4 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP The Algorithm Algorithm –EIGRP uses the Diffusing Update Algorithm (DUAL). –EIGRP does not send periodic updates and route entries do not age out out. –Only changes in the routing information, such as a new link or a li link becoming unavailable cause a routing update to occur. –EIGRP routing updates are still vectors of distances transmitted to directly connected neighbors. ITE PC v4.0 5 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP Path Determination –EIGRP's DUAL maintains a topology table separate from the routing table, which includes both the best path to a destination network and any backup destination network and any backup paths that DUAL has determined to be loop-free. –If a route becomes unavailable, DUAL If route becomes unavailable DUAL will search its topology table for a valid backup path. •If one exists, that route is If th immediately entered into the routing table. •If one does not exist, DUAL performs If DUAL a network discovery process to see if there happens to be a backup path that did not meet the requirement of that did not meet the requirement of the feasibility condition. ITE PC v4.0 6 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP Convergence –EIGRP does not use holddown timers. –Instead, loop-free paths are loop paths are achieved through a system of route calculations (diffusing computations) that are performed in coordinated that are performed in a coordinated fashion among the routers. –The detail of how this is done is beyond the scope of this course, but the result is faster convergence than traditional distance vector routing protocols. ITE PC v4.0 7 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP EIGRP Message Format EIGRP Header EIGRP Header Data link frame header - contains source and destination MAC address IP packet header - contains source & destination IP address EIGRP packet header - contains AS number AS number Type/Length/Field - data portion of EIGRP message In the IP packet header, the protocol field is set to 88 to indicate EIGRP the destination address is set to th the multicast 224.0.0.10. 224 If the EIGRP packet is encapsulated in an Ethernet frame, the destination MAC address is destination MAC address is also a multicast address: 01-00- 5E-00-00-0A. ITE PC v4.0 8 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP 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. EIGRP packet header EIGRP packet header contains –Opcode field •Update •Query •Reply •Hello –Autonomous System number • The AS number is used to track multiple instances of EIGRP. EIGRP Parameters contains –Weights •EIGRP uses for its composite metric. •By default, only bandwidth and delay are weighted. Both are set to 1. •The other K values are set to zero. –Hold time •The amount of time the EIGRP neighbor receiving this message neighbor receiving this message should wait before considering the advertising router to be down. ITE PC v4.0 9 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP TLV: IP internal contains (EIGRP routes within an autonomous system) –Metric field (Delay and Bandwidth) field (Delay and Bandwidth) •Delay is calculated as the sum of delays from source to destination in units of 10 microseconds. •Bandwidth is the lowest configured bandwidth of any interface along the route. –Subnet mask field •The subnet mask is specified as the prefix length or the number of network bits in the subnet mask. •255.255.255.0 is 24 –Destination field •the address of the destination network. add dest •Although only 24 bits are shown in this figure. •If a network address is longer than 24 bits, then the Destination field is extended for another 32 bits TLV: IP external contains –Fields used when external routes are imported into EIGRP routing process – import or redistribute a route into EIGRP. ITE PC v4.0 10 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP Protocol Dependent Modules (PDM) EIGRP EIGRP uses PDM to route several PDM different protocols i.e. IP, IPX & AppleTalk PDMs are responsible for the specific routing task for each network layer routing task for each network layer protocol –As you can see in the figure, EIGRP uses different EIGRP packets and maintains separate neighbor, topology, and routing tables for each Network layer protocol. •The IP-EIGRP module is responsible IP module is responsible for sending and receiving EIGRP packets that are encapsulated in IP and for using DUAL to build and maintain the IP routing table. How do people route How do people route •The IPX EIGRP module is IPX or Appletalk today responsible for exchanging routing if they still get either information about IPX networks with other IPX EIGRP routers other IPX EIGRP routers. IPX IPX or Appletalk? •Apple-Talk EIGRP is for Apple-talk ITE PC v4.0 11 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP Reliable Transport Protocol (RTP) Purpose of RTP of RTP –Used by EIGRP to transmit and receive EIGRP packets – EIGRP was designed as a Network layer independent routing protocol; therefore, it cannot use the services of UDP or TCP because IPX and Appletalk do not use protocols from the TCP/IP protocol suite. Characteristics of RTP –Involves both reliable & unreliable delivery of EIGRP packet Reliable delivery requires acknowledgment delivery requires acknowledgment from destination Unreliable delivery does not require an acknowledgement from destination –Packets can be sent Unicast Multicast –Using address 224.0.0.10 address 224 ITE PC v4.0 12 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP •Hello •Update EIGRP’s 5 Packet Types •ACK •Query Hello packets •Reply –Used to discover & form adjacencies with neighbors iscover orm djacencies with eighbors –EIGRP hello packets are multicasts and use unreliable delivery. ITE PC v4.0 13 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP •Hello •Update Update packets •ACK –Update packets are used to propagate packets are used to propagate routing information •Query –Update packets are sent only when •Reply necessary. –EIGRP updates are sent only to those routers that require it. –When a new neighbor is discovered, unicast update packets are sent so that the neighbor can build up its topology table. –In other cases, such as a link-cost change, updates are multicast. –Updates always are transmitted reliably Acknowledgement packets –Used to acknowledge receipt of update, query & reply packets •R2 has lost connectivity to the LAN attached to its FastEthernet interface. –An acknowledgment packet is a hello •R2 immediately sends an unicast Update packet that has no data. to R1 and R3 noting the downed route. –EIGRP acknowledgement packets are EIGRP acknowledgement packets are •R1 and R3 respond with an unicast always sent as an unreliable unicast acknowledgement. ITE PC v4.0 14 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
•Hello EIGRP •Update •ACK Query & Reply packets •Query Used by DUAL for searching for •Reply networks networks Queries and replies use reliable delivery. Query packets can use Multicast Reply packet use only unicast •R2 has lost connectivity to the LAN has lost connectivity to the LAN and it sends out queries to all EIGRP neighbors. •All neighbors must send a reply regardless of whether or not they have a route to the downed network. ITE PC v4.0 15 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP Acknowledge Query Update Reply Hello Reliable Reliable Reliable Unreliable Unreliable (not require (a hello packet that acknowledgment ) has no data ) multicast Multicast & unicast multicast unicast unicast ITE PC v4.0 16 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP Purpose of Hello Protocol –To discover neighbors & establish adjacencies with neighbor routers To discover neighbors establish neighbor routers Characteristics of hello protocol –Time interval for sending hello packet interval for sending hello packet 5 seconds - high bandwidth (greater than T1) 60 seconds - multipoint circuits T1 bandwidth or slower -Holdtime This is the maximum time router should wait before declaring a neighbor down Default holdtime –3 times hello interval »15 seconds »180 seconds ITE PC v4.0 17 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP EIGRP Bounded Updates EIGRP only sends update when there is a change in route status Partial update –A partial update includes only the route information that has changed – the whole routing table is NOT sent Bounded update update –When a route changes, only those devices that are impacted will be notified of the change EIGRP’s use of partial bounded updates minimizes use of bandwidth ITE PC v4.0 18 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP EIGRP Diffusing Update Algorithm (DUAL) Al (DUAL) –Purpose •EIGRP’s primary method for preventing routing loops •And also hold-down timers and split horizon, too. –Advantage of using DUAL •Provides for fast convergence time by keeping a list of loop- ti li free backup routes –DUAL maintains a list of backup routes it has already determined to be loop-free. If the primary route in the routing table fails, the best backup route is immediately added to the routing table. ITE PC v4.0 19 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP Administrative Distance (AD) –Defined as the trustworthiness of the source route EIGRP default administrative distances –Summary routes = 5 routes –Internal routes = 90 –Imported routes = 170 ITE PC v4.0 20 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

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