routing protocols and concepts
DESCRIPTION
Routing Protocols and Concepts . EIGRP Chapter 9 Modified by Pete Brierley. What will we Learn from chapter 9?. Describe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP). Examine the basic EIGRP configuration commands and identify their purposes. - PowerPoint PPT PresentationTRANSCRIPT
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1
Routing Protocols and Concepts
EIGRPChapter 9Modified by Pete Brierley
ITE PC v4.0Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
What will we Learn from chapter 9?
Describe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP).
Examine the basic EIGRP configuration commands and identify their purposes.
Calculate the composite metric used by EIGRP.
Describe the concepts and operation of DUAL.
Describe the uses of additional configuration commands in EIGRP.
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Introduction
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Terms you MUST knowRIPng
Weights
Hold time
TLV
Neighbor Table
Routing Table
Topology Table
Bounded Updates
Summary routes
Quan zeros
AS
Wildcard mask
IPv6
K values
Reliability
Load
Delay
Bandwidth
Successor
Feasible Distance
RD
FC
Feasible Successor
FSM
Internal routes
External routes
OP Code
PDM
RTP
Unicast
Multicast
Hello packet
Adjacencies
DUAL
IANA
Null 0
Aperiodic
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EIGRP Roots of EIGRP: IGRP
-Developed in 1985 to overcome RIPv1’s limited hop count-Distance vector routing protocol-Metrics used by IGRP
bandwidth (used by default)Delay (used by default)reliabilityload
-IGRP discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S
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EIGRPEIGRP Message Format
EIGRP HeaderData link frame header - contains source and destination MAC addressIP packet header - contains source & destination IP addressEIGRP packet header - contains AS numberType/Length/Field - data portion of EIGRP message
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EIGRP
EIGRP packet header contains
–Opcode field–Autonomous System number
EIGRP Parameters contains–Weights –Hold time
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EIGRP
TLV: IP internal contains–Metric field–Subnet mask field–Destination field
TLV: IP external contains–Fields used when external routes are imported into EIGRP routing process
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EIGRPProtocol Dependent
Modules (PDM) EIGRP uses PDM to route
several different protocols i.e. IP, IPX & AppleTalk
PDMs are responsible for the specific routing task for each network layer protocol
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EIGRPReliable Transport Protocol (RTP) Purpose of RTP
–Used by EIGRP to transmit and receive EIGRP packets
Characteristics of RTP–Involves both reliable & unreliable delivery of EIGRP packet
Reliable delivery requires acknowledgment from destinationUnreliable delivery does not require an acknowledgement from destination
–Packets can be sent UnicastMulticast
–Using address 224.0.0.10
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EIGRPEIGRP’s 5 Packet Types
Hello packets–Used to discover & form adjacencies with neighbors
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EIGRP Update packets
–Used to propagate routing information
Acknowledgement packets
–Used to acknowledge receipt of update, query & reply packets
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EIGRP Query & Reply packets
Used by DUAL for searching for networksQuery packets
-Can use UnicastMulticast
Reply packet -Use only
unicast
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EIGRP Purpose of Hello Protocol
–To discover & establish adjacencies with neighbor routers
Characteristics of hello protocol–Time interval for sending hello packet
Most networks it is every 5 secondsMultipoint non broadcast multi-access networks
–Unicast every 60 seconds-Holdtime
This is the maximum time router should wait before declaring a neighbor downDefault holdtime
–3 times hello interval
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EIGRPEIGRP 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–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
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EIGRP
Diffusing Update Algorithm (DUAL)–Purpose
•EIGRP’s primary method for preventing routing loops–Advantage of using DUAL
•Provides for fast convergence time by keeping a list of loop-free backup routes
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EIGRP
Administrative Distance (AD)–Defined as the trustworthiness of the source route
EIGRP default administrative distances–Summary routes = 5–Internal routes = 90–Imported routes = 170
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EIGRP
Authentication EIGRP can
– Encrypt routing information
– Authenticate routing information
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EIGRPNetwork Topology Note the ISP router
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EIGRP EIGRP will automatically
summarize routes at classful boundaries
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EIGRP
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Basic EIGRP Configuration Autonomous System (AS) & Process IDs
–This is a collection of networks under the control of a single authority (reference RFC 1930)–AS Numbers are assigned by IANA
–Entities needing AS numbersISPInternet Backbone prodiersInstitutions connecting to other institutions using AS numbers
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Basic EIGRP Configuration EIGRP autonomous system
number actually functions as a process ID
Process ID represents an instance of the routing protocol running on a router
ExampleRouter(config)#router
eigrp autonomous-system
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Basic EIGRP ConfigurationThe router eigrp command
The global command that enables eigrp isrouter eigrp autonomous-system -All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number)
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Basic EIGRP ConfigurationThe Network Command
Functions of the network command–Enables interfaces to transmit & receive EIGRP updates–Includes network or subnet in EIGRP updates
Example–Router(config-router)#network network-address
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Basic EIGRP Configuration The network Command with a Wildcard Mask
-This option is used when you want to configure EIGRP to advertise specific subnets-Example Router(config-router)#network network-address [wildcard-mask]
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Basic EIGRP ConfigurationVerifying EIGRP EIGRP routers must establish adjacencies with their neighbors before
any updates can be sent or received
Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is
show ip eigrp neighbors
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EIGRP
The show ip protocols command is also used to verify that EIGRP is enabled
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Basic EIGRP Configuration
Examining the Routing Table
The show ip route command is also used to verify EIGRP
EIGRP routes are denoted in a routing table by the letter “D”
By default , EIGRP automatically summarizes routes at major network boundary
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Basic EIGRP Configuration Introducing the Null0 Summary Route
–Null0 is not a physical interface–In the routing table summary routes are sourced from Null0
Reason: routes are used for advertisement purposes–EIGRP will automatically include a null0 summary route as child route when 2 conditions are met
At least one subnet is learned via EIGRPAutomatic summarization is enabled
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Basic EIGRP Configuration R3’s routing table shows
that the 172.16.0.0/16 network is automatically summarized by R1 & R3
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EIGRP Metric CalculationEIGRP Composite Metric & the K Values EIGRP uses the following values in its composite metric
-Bandwidth, delay, reliability, and load The composite metric used by EIGRP
– formula used has values K1 K5K1 & K3 = 1all other K values = 0
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EIGRP Metric Calculation Use the sh ip protocols command to verify the K
values
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EIGRP Metric CalculationEIGRP Metrics
Use the show interfaces command to view metrics
EIGRP MetricsBandwidth – EIGRP uses a static bandwidth to calculate metricMost serial interfaces use a default bandwidth value of 1.544Mbos (T1)
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EIGRP Metric CalculationEIGRP Metrics
Delay is the defined as the measure of time it takes for a packet to traverse a route
-it is a static value based on link type to which interface is connected
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EIGRP Metric Calculation Reliability (not a default EIGRP metric)
-A measure of the likelihood that a link will fail-Measure dynamically & expressed as a fraction of 255
the higher the fraction the better the reliability
Load (not a default EIGRP metric)– A number that reflects how much traffic is using a link– Number is determined dynamically and is expressed as a fraction of 255
The lower the fraction the less the load on the link
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EIGRP Metric CalculationUsing the Bandwidth Command
Modifying the interface bandwidth
-Use the bandwidth command-ExampleRouter(config-if)#bandwidth kilobits
Verifying bandwidth –Use the show interface command
Note – bandwidth command does not change the link’s physical bandwidth
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EIGRP Metric Calculation The EIGRP metric can be determined by examining the
bandwidth delay
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EIGRP Metric Calculation
EIGRP uses the lowest bandwidth (BW)in its metric calculation
Calculated BW = reference BW / lowest BW(kbps)
Delay – EIGRP uses the cumulative sum of all outgoing interfaces
Calculated Delay = the sum of outgoing interface delays
EIGRP Metric = calculated BW + calculated delay
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EIGRP Metric Calculation
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EIGRP Metric Calculation
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EIGRP Metric Calculation
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DUAL Concepts
The Diffusing Update Algorithm (DUAL) is used to prevent looping
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DUAL Concepts Successor
The best least cost route to a destination found in the routing table
Feasible distanceThe lowest calculated metric along a path to a destination network
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DUAL ConceptsFeasible Successors, Feasibility Condition & Reported
Distance
Feasible Successor
-This is a loop free backup route to same destination as successor route
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DUAL Concepts
Reported distance (RD)
-The metric that a router reports to a neighbor about its own cost to that network
Feasible Successors, Feasibility Condition & Reported Distance
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DUAL Concepts
Feasibility Condition (FC)
-Met when a neighbor’s RD is less than the local router’s FD to the same destination network
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DUAL Concepts
EIGRP Topology Table dissected
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DUAL ConceptsTopology Table: No Feasible Successor A feasible successor may not be present because the
feasibility condition may not be met-In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance
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DUAL Concepts
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DUAL Concepts Finite Sate Machine (FSM)
–An abstract machine that defines a set of possible states something can go through, what event causes those states and what events result form those states–FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events
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DUAL Concepts
DUAL FSM–Selects a best loop-free path to a destination–Selects alternate routes by using information in EIGRP tables
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DUAL ConceptsFinite State Machines (FSM)
To examine output from EIGRP’s finite state machine us the debug eigrp fsm command
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More EIGRP Configurations
The Null0 Summary Route By default, EIGRP uses the Null0 interface to discard
any packets that match the parent route but do not match any of the child routes
EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist
–One or subnets exists that was learned via EIGRP–Automatic summarization is enabled
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More EIGRP ConfigurationsThe Null0 Summary Route
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More EIGRP Configurations
Disabling Automatic Summarization The auto-summary command permits EIGRP to
automatically summarize at major network boundaries The no auto-summary command is used to disable
automatic summarization–This causes all EIGRP neighbors to send updates that will not be automatically summarized
this will cause changes to appear in both -routing tables -topology tables
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More EIGRP Configurations
Manual Summarization
Manual summarization can include supernetsReason: EIGRP is a classless routing protocol & include subnet mask in update
Command used to configure manual summarization –Router(config-if)#ip summary-address eigrp as-number
network-address subnet-mask
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More EIGRP Configurations Configuring a summary route in EIGRP
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More EIGRP Configurations
EIGRP Default Routes
“quad zero” static default route-Can be used with any currently supported routing protocol-Is usually configured on a router that is connected a network outside the EIGRP domain
EIGRP & the “Quad zero” static default route–Requires the use of the redistribute static command to disseminate default route in EIGRP updates
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More EIGRP ConfigurationsFine-Tuning EIGRP
EIGRP bandwidth utilization-By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information-The command to change the percentage of bandwidth used by EIGRP is
Router(config-if)#ip bandwidth-percent eigrp as-number percent
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More EIGRP Configurations Configuring Hello Intervals and Hold Times
-Hello intervals and hold times are configurable on a per-interface basis-The command to configure hello interval is
Router(config-if)#ip hello-interval eigrp as-number seconds
Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval
-The command to configure hold time value isRouter(config-if)#ip hold-time eigrp as-number seconds
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Summary Background & History
–EIGRP is a derivative of IGRPEIGRP is a Cisco proprietary distance vector routing protocol released in 1994
EIGRP terms and characteristics–EIGPR uses RTP to transmit & receive EIGRP packets–EIGRP has 5 packet type:
Hello packetsUpdate packetsAcknowledgement packetsQuery packetsReply packets
–Supports VLSM & CIDR
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Summary
EIGRP terms and characteristics–EIGRP uses a hello protocol
Purpose of hello protocol is to discover & establish adjacencies
–EIGRP routing updatesAperiodicPartial and boundedFast convergence
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Summary
EIGRP commands–The following commands are used for EIGRP configuration
RtrA(config)#router eigrp [autonomous-system #]RtrA(config-router)#network network-number
–The following commands can be used to verify EIGRPShow ip protocolsShow ip eigrp neighborsShow ip route
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Summary
EIGRP metrics include–Bandwidth (default)–Delay (default)–Reliability–Load
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Summary DUAL
–Purpose of DUALTo prevent routing loops
–SuccessorPrimary route to a destination
–Feasible successorBackup route to a destination
–Feasible distanceLowest calculated metric to a destination
–Reported distanceThe distance towards a destination as advertised by an upstream neighbor
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Summary Choosing the best route
–After router has received all updates from directly connected neighbors, it can calculate its DUAL
1st metric is calculated for each route2nd route with lowest metric is designated successor & is placed in routing table3rd feasible successor is found
–Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distance–Feasible routes are maintained in topology table
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Summary
Automatic summarization–On by default–Summarizes routes on classful boundary–Summarization can be disabled using the following command
RtrA(config-if)#no auto-summary
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EIGRP
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EIGRP
Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol based on IGRP.
EIGRP supports CIDR, and hence VLSM.
Compared to IGRP, EIGRP boasts faster convergence times, improved scalability and superior handling of routing loops.
Technically, EIGRP is an advanced distance-vector routing protocol that relies on features commonly associated with link-state protocols. Some of OSPF’s best traits, such as partial updates & neighbor discovery, are similarly put to use by EIGRP.
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EIGRP
Recall that OSPF’s strengths include scalability and multi-vendor support. So if your core routers are a mixed bag of products from several different vendors, OSPF and RIP may be your only options.
But OSPF’s benefits, especially it’s hierarchical design, come at a price: administrative complexity.
EIGRP is an ideal choice for large, multiprotocol networks built primarily on Cisco routers (says Cisco).
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Comparison of OSPF and EIGRP
OSPF EIGRPSupports CIDR & VLSM, rapid convergence, partial updates, neighbor discovery.
Supports CIDR & VLSM, rapid convergence, partial updates, neighbor discovery
Enables the admin to define route summarization.
Uses automatic route summarization & user-defined route summaries.
Is an open standard; has multi-vendor support
Is proprietary; can only be used with Cisco routers.
Is scalable; admin defined ‘areas’ provide manageable hierarchy.
Is scalable; no hierarchical domains exist
Is difficult to implement Is easy to implement.
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EIGRP and IGRP Compatibility
EIGRP offers multiprotocol support and IGRP does not.
EIGRP scales IGRP’s metric by a factor of 256. That’s because EIGRP uses a metric that is 32 bits long, & IGRP uses a 24-bit metric. By dividing or multiplying by 256, EIGRP can easily exchange information with IGRP.
EIGRP imposes a max hop limit of 224, where IGRP has 255.
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Sharing or redistribution, is automatic between IGRP & EIGRP as long as both processes use the same AS number.
metric = [K1 x bandwidth + K2 x bandwidth) / (256ms – load) + (K3 x delay)] x [K5 / (reliability+K4)]
Where by default: K1 = 1 K2 = 0 K3 = 1 K4 = 0 K5 = 0
EIGRP and IGRP Compatibility
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EIGRP tags routes learned from IGRP as external because they did not originate from EIGRP routers. External EIGRP routes are denoted by EX in the routing table.
But IGRP cannot differentiate between internal & external routes
EIGRP vs. IGRP
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EIGRP
EIGRP is an advanced distance vector routing protocol, but has advantages over simple distance vector protocols:
• rapid convergenceBy using an routing algorithm, Diffusing Update Algorithm (DUAL) which guarantees loop-free operation & allows all routers involved in a topology change to synchronize at the same time.
• partial bounded updatesEIGRP routers make partial, incremental updates, & unlike OSPF, the routers send these partial updates only to the routers that need the information. This is called bounded updates.
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EIGRP cont.• minimal consumption of bandwidth when the network is stable
•No timed routing updates - instead small hello packets. •Exchanged a regular intervals •don’t use a significant amount of bandwidth.
• support for VLSM and CIDR• multiple network-layer support
EIGRP supports IP, IPX and AppleTalk via protocol-dependent modules (PDM).
• complete independence from routed protocolsPDM protect EIGRP from painstaking revision.
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EIGRP Terminology & Tables
EIGRP routers keep route and topology information in RAM for quick access.
EIGRP terms and tables:neighbor tableMaintains a neighbor table that list adjacent routers. There is a neighbor table for each protocol that EIGRP supports.
topology tableTopology table for each configured network protocol. All learned routes to a destination are maintained in the topology table.
routing tableEIGRP chooses the best (successor) routes to a destination from the topology table & places these routes in the routing table.
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successora route selected as the primary route used to reach a destination. Successors are kept in the routing table.
feasible successorIs a backup route. They are kept in the topology table.
EIGRP routers establish adjacencies with neighbor routers by sending hello packets, sent every 5 seconds (default).
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.
EIGRP Terminology
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EIGRP Technologies cont.
Reliable Transport Protocol (RTP) is a transport layer (layer 4) protocol that can guarantee ordered delivery of EIGRP packets to all neighbors. To stay independent of IP, EIGRP uses its own proprietary transport-layer protocol to guarantee delivery of routing information.
EIGRP uses RTP to provide reliable or unreliable service as the situation warrants. Hello packets are not required to be reliable delivery. RTP supports both unicasting & multicasting , and it can multicast and unicast to different peers simultaneously.
The centerpiece of EIGRP is DUAL, the EIGRP route calculation engine. It uses a finite state machine.
DUAL tracks all the routes advertised by neighbors and uses the composite metric of each route to compare them. DUAL also guarantees that each path is loop-free.
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EIGRP Technologies cont.
A successor is a neighboring router that is currently used for packet forwarding; it provides the least cost route to the destination and is not part of the routing loop
A feasible successor provides the next lowest cost path without introducing routing loops.
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EIGRP Data Structure
Neighbor TableRouting TableTopology Table
Reported distance (RD) Feasible distance (FD)
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EIGRP Data Structure
Neighbor Tablethe most important table in EIGRP. The neighbor relationships in the neighbor table are basis for all EIGRP routing updates and convergence activity. supports reliable, sequenced delivery of packets.
Routing TableContain the routes installed by DUAL as the best loop free paths to a given destination. It canmaintain up to 4 routes per destination.Topology Tablestores all the information it needs to calculate a set of distances and vectors to all reachable destinations.
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EIGRP Data Structure
Reported distance (RD) The distance reported by an adjacent neighbor to a specific destination.
Feasible distance (FD) The lowest calculated metric to each destination.
Table is sorted with the successor routes at the top, followed by feasible successors.
At the bottom are what DUAL believes are routing loops.
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To see the topology table, use the command:
Router# show ip eigrp topology [all]
Example of output:
P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33
via 10.2.0.2 (2681856/2169856), Serial1
Viewing (2681856/2169856), 2681856 is the FD, and 2169856 is the RD.
If no feasible successors to the destination exist, DUAL places the route in the active state.
Entries in the topology table can be in one of 2 states• passive route – route that is stable and available for use
• active route – route in the process of being recomputed by DUAL.
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Internal routes originate from within the EIGRP AS.
External routes originate from outside the system.
Routes learned (redistributed) from other routing protocols such as RIP, OSPF and IGRP are external.
Static routes originating from outside the EIGRP AS and redistributed inside are also external routes.
NOTE:
The internal administrative distance of EIGRP is 90.
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EIGRP Packet Types
EIGRP relies on 5 packet types to maintain its various tables and establish complex relationships with neighbor routers.
The 5 packet types:1. Hello2. Acknowledgment3. Update4. Query5. Reply
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Hello PacketsEIGRP relies on hello packets to discover, verify & rediscover neighbor
routers. The default hello interval depends on the bandwidth of the interface:
Bandwidth Example Link Default Hello Default HoldInterval Time
Less than 1.544Mbps Multipoint Frame Relay 60 sec 180 sec
Greater than 1.544Mbps T1, Ethernet 5 sec 15 sec
Keep the hold timer 3 times the hello interval. EIGRP hello packets are multicast. On IP networks,
EIGRP routers send hellos to the multicasts IP address 224.0.0.10.
Recall that OSPF requires neighbor routers to have the same hello & dead intervals to communicate. EIGRP has no such restriction.
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Acknowledgement Packets
An EIGRP router uses acknowledgement packets to indicate receipt of any EIGRP packet during a reliable exchange.
To be reliable, a sender’s message must be acknowledged by the recipient.
Hello packets are always sent unreliable, & require no acknowledgement.
Update Packets
Update packets are used when a router discovers a new neighbor. They are also used when a router detects a topology change.
All update packets are sent reliably.
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Query and Reply Packets
EIGRP routers use query packets whenever they need specific information from one or all of its neighbors. A reply packet is used to respond to a query.
Query can be multicast or unicast
Replies are always unicast.
Both packet types are sent reliably.
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EIGRP Convergence (DUAL)
DUAL’s sophisticated algorithm results in EIGRP’s exceptional fast convergence, says Cisco
A router’s topology table includes a list of all routes advertised by the neighbors. For each network, the router keeps the real (computed) cost of getting to that network & also keeps the advertised cost (reported distance) from its neighbor.
ITE PC v4.0Chapter 1 93© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
The best path is the path with the lowest metric route that is calculated by adding the metric between the next-hop router and the destination (the reported distance) to the metric between the local router and the next-hop router.
This computed cost, or distance is the FD.
The next-hop router(s) are selected as the best path is the successor. If several routes have the same FD, then there can be several successors to a destination.
EIGRP Convergence (DUAL)
ITE PC v4.0Chapter 1 94© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
RTA
RTX
RTZ
FDDI
Network24
RTY
COST
Serial10
100 100
10
20
1
Neighbor Computed Cost to 24 Report Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220
10
For RTA, RTY is the successor to Network 24, because it has the lowest computed cost (31). Hence RTA’s FD=31.
If RTY goes down, then is there a feasible successor – or not? If so, what is it?
RTA reaches Network 24 via:
ITE PC v4.0Chapter 1 95© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
RTA
RTX
RTZ
FDDI
Network24
RTY
COST
Serial10
100 100
10
20
1
Neighbor Computed Cost to 24 Report Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220
10
Feasible successor =
1. It’s RD < RTA’s FD AND2. Has the lowest computed cost of all other routes
DUAL calculates the feasible successor to be through RTX
Remember: RTA’s FD=31
ITE PC v4.0Chapter 1 96© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
RTA
RTX
RTZ
FDDI
Network24
RTY
COST
Serial10
100 100
10
20
1
Neighbor Computed Cost to 24 Reported Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220
10
Feasible successor =1. It’s RD < RTA’s FD AND2. Has the lowest computed cost of all other routes
Suppose RTX also goes down. Is there a feasible successor for RTA to Network 24?
NO! DUAL will set the route to Network 24 from passive to active state, and RTA will query its neighbor’s about Network 24 again.
ITE PC v4.0Chapter 1 97© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Consider the output from the command ‘show ip eigrp topology all’:
P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33via 10.2.0.2 (2681856/2169856), Serial0via 10.2.1.2 (2681856/2169856), Serial1via 10.2.2.2 (2891856/2769856), Ethernet 0
Remember:Successor is the route that has the best lowest cost or FD.Feasible successor =
It’s RD < link’s FD AND has the lowest computed cost of all other routes
ITE PC v4.0Chapter 1 98© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Consider the output from ‘show ip eigrp topology all’:
P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33via 10.2.0.2 (2681856/2169856), Serial0via 10.2.1.2 (2681856/2169856), Serial1via 10.2.2.2 (2891856/2769856), Ethernet 0
What are the successor(s)?
10.2.0.2 AND 10.2.1.2
What are the feasible successor(s)?
NONE
ITE PC v4.0Chapter 1 99© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
EIGRP Operation
The 4 key steps to EIGRP operation are:1. building the neighbor table2. discovering routes3. choosing routes4. maintaining routes
Choose the routes based on these 5 factors:1. bandwidth2. delay3. reliability4. load5. MTU (maximum transmission unit)
So, unless otherwise configured by an administrator, bandwidth & delay are the only 2 factors that determine EIGRP’s metric value.
ITE PC v4.0Chapter 1 100© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Configuring EIGRP
Configuring EIGRP for IP Networks
Router(config)# router eigrp autonomous-system-number
Router(config-router)# network network-number
network-number is the NETWORK address of the interface of the router
ITE PC v4.0Chapter 1 101© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Configuring EIGRP
The ip bandwidth-percent command configures the percentage of bandwidth that EIGRP can use on an interface.
By default, EIGRP is set to use up to 50 percent of the bandwidth of an interface to exchange routing information.
The command relies on the bandwidth of an interface.
Some cases the engineer sets the bandwidth to a lower number than the actual bandwidth of the link (in order to manipulate the routing metric).
ITE PC v4.0Chapter 1 102© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Summarizing EIGRP routes for IP
EIGRP automatically summarizes routes at a classful boundary.For discontiguous subnetworks, you do NOT want summarization.The command that turns summarization off on EIGRP is:
Router(config-router)# no auto-summaryHence, with summarization turned off, EIGRP routers will advertise subnets.
ITE PC v4.0Chapter 1 103© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Manual summary routes are configured on a per-interface basis by:
Router(config-if)#ip summary-address eigrp autonomous-system-number ip-address mask administrative-distance
By default, EIGRP summary routes have an administrative distance of 5. The value can range between 1 and 255.
Summarizing EIGRP routes for IP
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What did I Learn from chapter 9?
Describe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP).
Examine the basic EIGRP configuration commands and identify their purposes.
Calculate the composite metric used by EIGRP.
Describe the concepts and operation of DUAL.
Describe the uses of additional configuration commands in EIGRP.
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ENDEIGRP
NextLink State Routing Protocols