Transcript EIGRP - smk2tutorial

Protokol Dan Konsep
Routing
EIGRP
Chapter 9
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Objektif

Menerangkan tentang latarbelakang dan sejarah
Enhanced Interior Gateway Routing Protocol
(EIGRP).

Mengenalpasti arahan asas konfigurasi EIGRP dan
tujuannya

Mengira composite metric menggunakan EIGRP.

Menerangkan konsep dan operasi DUAL.

Menerangkan penggunaan penambahan arahan
konfigurasi dalam EIGRP.
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Pengenalan
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Istilah yang perlu tahu “MUST KNOW”
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RIPng
Internal routes
IPv6
Weights
External routes
K values
Hold time
OP Code
Reliability
TLV
PDM
Load
Neighbor Table
RTP
Delay
Routing Table
Unicast
Bandwidth
Topology Table
Multicast
Successor
Bounded Updates
Hello packet
Feasible Distance
Summary routes
Adjacencies
RD
Quan zeros
DUAL
FC
AS
IANA
Feasible Successor
Wildcard mask
Null 0
FSM
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EIGRP
 Sejarah EIGRP: IGRP
-dibagunkan pada tahun 1985 bermula
dengan RIPv1’s hop count yang terhad
-Distance vector routing protocol
-IGRP menggunakan metrik
bandwidth (used by default)
Delay (used by default)
reliability
load
- IGRP tidak dapat disokong dengan
IOS 12.2(13)T & 12.2(R1s4)S
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EIGRP
Format mesej EIGRP
 EIGRP Header
Data link frame header – mengndungi sumber dan alamat
destinasi MAC
IP packet header - mengndungi sumber dan alamat destinasi IP
EIGRP packet header - mengandungi nombor AS
Type/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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EIGRP
Protocol Dependent
Modules (PDM)
 EIGRP menggunakan PDM to
route several different
protocols i.e. IP, IPX &
AppleTalk
 PDMsbertanggungjawab
kepada tugas routing yang
spesifik bagi setiap lapisan
protokol rangkaian
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EIGRP
Reliable Transport Protocol (RTP)
 Tujuan RTP
–Digunakan oleh EIGRP untuk menghantar
dan menerima EIGRP packets
 Ciri-ciri RTP
–Melibatkan penghantaran yang boleh
dipercayai(reliable) dan tidak boleh dipercayai
(unreliable) oleh EIGRP packet
Memerlukan penghantaran yang boleh
dipercayai
Pengesahan daripada destinasi
Penghantaran yang tidak boleh
dipercayai tidak memerlukan pengesahan
dari destinasi
–Paket akan menghantar
Unicast
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Multicast
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EIGRP
5 Jenis Paket EIGRP’s
 Hello packets
–Used to discover & form adjacencies with neighbors
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EIGRP
 Update packets
 Digunakan untuk
menyebarkan maklumat
routing
 Acknowledgement
packets
–Digunakan untuk mengakui
penerimaan paket update,
pertanyaan & jawapan
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EIGRP
 Query & Reply packets
Digunakan oleh DUAL untuk
carian rangkaian
Query packets
-boleh menggunakan
Unicast
Multicast
Reply packet
-hanya menggunakan
unicast
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EIGRP
 Tujuan Hello Protocol
–To discover & establish adjacencies with neighbor routers
 Ciri-ciri hello protocol
–Time interval for sending hello packet
Most networks it is every 5 seconds
Multipoint non broadcast multi-access networks
–Unicast every 60 seconds
-Holdtime
This is the maximum time
router should wait before
declaring a neighbor down
Default holdtime
–3 times hello interval
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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
–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 loopfree 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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EIGRP
Network 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 numbers
ISP
Internet Backbone prodiers
Institutions connecting to other institutions using AS
numbers
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Konfigurasi asas EIGRP
 EIGRP autonomous system
number actually functions as
a process ID
 Process ID represents an
instance of the routing
protocol running on a router
 Example
Router(config)#router
eigrp autonomous-system
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Konfigurasi asas EIGRP
Arahan router eigrp
 The global command that enables eigrp is
router eigrp autonomous-system
-All routers in the EIGRP routing domain must use
the same process ID number (autonomous-system
number)
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Konfigurasi asas EIGRP
Arahan Network
 Fungsi arahan network
–Membolehkan pengemaskinian
antaramuka untuk menghantar
& menerima EIGRP
–Pengemaskinian dalam EIGRP
termasuk rangkaian & subnet
–Router(config-router)#network
network-address
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Konfigurasi asas EIGRP
 Arahan rangkaian dengan Wildcard Mask
-Pilihan ini digunakan apabila anda hendak
mengkonfigurasi EIGRP untuk mengiklan subnets tertentu
--Example
Router(config-router)#network network-address [wildcard-mask]
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Konfigurasi asas EIGRP
Pengesahan 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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Konfigurasi asas EIGRP
Examining the Routing
Table
 Arahan show ip route untuk
pengesahan EIGRP
 EIGRP routes akan
ditandakan dengan huruf
“D” di dalam jadual routing
 By default , EIGRP
automatically summarizes
routes at major network
boundary
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Konfigurasi asas EIGRP
 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 EIGRP
Automatic summarization is enabled
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Konfigurasi asas EIGRP
 R3’s routing table shows
that the 172.16.0.0/16
network is automatically
summarized by R1 & R3
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Pengiraan metrik EIGRP
EIGRP 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 K5
K1 & K3
=1
all other K values = 0
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Pengiraan metrik EIGRP
 Use the sh ip protocols command to verify the K
values
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Pengiraan metrik EIGRP
EIGRP Metrics
 arahan show
interfaces untuk
menunjukkan metrik
 EIGRP Metrics
Bandwidth – EIGRP
menggunakan
bandwidth statik untuk
mengira metrik
Kebanyakkan
antaramuka siri (serial
interface) menggunakan
nilai default bandwidth
1.544Mbos (T1)
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Pengiraan metrik EIGRP
EIGRP Metrics
 Delay – jarak masa yang diperlukan oleh satu paket
untuk merentasi route
-merupakan nilai statik berdasarkan jenis link
antaramuka yang berkaitan
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Pengiraan metrik EIGRP
 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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Pengiraan metrik EIGRP
Menggunakan arahan Bandwidth
 Mengubahsuai antaramuka
bandwidth
-menggunakan arahan bandwidth
-contoh
Router(config-if)#bandwidth
kilobits
 pengesahan bandwidth
–Menggunakan arahan show
interface
 Note – bandwidth command
does not change the
link’s physical
bandwidth
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Pengiraan metrik EIGRP
 The EIGRP metric can be determined by examining the
bandwidth delay
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Pengiraan metrik EIGRP
 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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Pengiraan metrik EIGRP
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Pengiraan metrik EIGRP
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Pengiraan metrik EIGRP
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Konsep DUAL
 Diffusing Update Algorithm (DUAL) diguinakan untuk
mengelakkan looping
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Konsep DUAL
 Successor
The best least cost
route to a destination
found in the routing
table
 Feasible distance
The lowest
calculated metric
along a path to a
destination network
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Konsep DUAL
Feasible Successors, Feasibility Condition & Reported
Distance
 Feasible
Successor
-This is a loop
free backup
route to same
destination as
successor route
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Konsep DUAL
Feasible Successors, Feasibility Condition & Reported
Distance
 Reported distance
(RD)
-The metric that a
router reports to a
neighbor about its
own cost to that
network
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Konsep DUAL
 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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Konsep DUAL
 EIGRP
Topology
Table
dissected
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Konsep DUAL
Topology 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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Konsep DUAL
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Konsep DUAL
 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
–Memilih bahagian
terbaik loop-free ke
destinasi
–Memilih laluan
alternatif
menggunakan
maklumat di dalam
jadual EIGRP
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DUAL Concepts
Finite State Machines (FSM)
 To examine output from EIGRP’s finite state machine
us the debug eigrp fsm command
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Tambahan Konfigurasi EIGRP
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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Tambahan Konfigurasi EIGRP
The Null0 Summary Route
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Tambahan Konfigurasi EIGRP
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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Tambahan Konfigurasi EIGRP
Manual Summarization
 Manual summarization can include supernets
Reason: 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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Tambahan Konfigurasi EIGRP
 Configuring a summary route in EIGRP
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Tambahan Konfigurasi EIGRP
EIGRP Default Routes
 “quad zero” static default route
-boleh mengunakan mana-mana routing untuk
menyokong protokol
-kebiasaannya konfiger router di sambung dengan
rangkaian luar domain EIGRP
 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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Tambahan Konfigurasi EIGRP
Fine-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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Tambahan Konfigurasi EIGRP
 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 is
Router(config-if)#ip hold-time eigrp as-number seconds
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Summary
 Background & History
–EIGRP is a derivative of IGRP
EIGRP 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 packets
Update packets
Acknowledgement packets
Query packets
Reply 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 updates
Aperiodic
Partial and bounded
Fast 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 EIGRP
Show ip protocols
Show ip eigrp neighbors
Show ip route
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Summary
 EIGRP metrics include
–Bandwidth (default)
–Delay (default)
–Reliability
–Load
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Summary
 DUAL
–Purpose of DUAL
To prevent routing loops
–Successor
Primary route to a destination
–Feasible successor
Backup route to a destination
–Feasible distance
Lowest calculated metric to a destination
–Reported distance
The 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 route
2nd route with lowest metric is designated
successor & is placed in routing table
3rd 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 multivendor 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
Supports CIDR & VLSM, rapid
convergence, partial updates,
neighbor discovery.
Enables the admin to define
route summarization.
Is an open standard; has
multi-vendor support
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EIGRP
Supports CIDR & VLSM, rapid
convergence, partial updates,
neighbor discovery
Uses automatic route
summarization & user-defined
route summaries.
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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EIGRP and IGRP
Compatibility
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:
= 0 K5 = 0
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K1 = 1
K2 = 0
K3 = 1
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EIGRP vs. IGRP
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
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EIGRP
EIGRP is an advanced distance vector routing protocol, but has
advantages over simple distance vector protocols:
• rapid convergence
By 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 updates
EIGRP 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 protocoldependent modules
(PDM).
• complete independence from routed protocols
PDM 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 table
Maintains a neighbor table that list adjacent routers. There is a
neighbor table for each protocol that EIGRP supports.
topology table
Topology table for each configured network protocol. All learned
routes to a destination are maintained in the topology table.
routing table
EIGRP chooses the best (successor) routes to a destination from
the topology table & places these routes in the routing table.
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EIGRP
Terminology
successor
a route selected as the primary route used to reach a destination.
Successors are kept in the routing table.
feasible successor
Is 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.
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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 Table
Routing Table
Topology Table
Reported distance (RD)
Feasible distance (FD)
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EIGRP Data Structure
Neighbor Table
the 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 Table
Contain the routes installed by DUAL as the best loop free
paths to a given destination. It canmaintain up to 4 routes
per destination.
Topology Table
stores 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. Hello
2. Acknowledgment
3. Update
4. Query
5. Reply
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Hello
Packets
EIGRP 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 Hold
Interval
Less than 1.544Mbps
Multipoint Frame Relay
Greater than 1.544Mbps T1, Ethernet
Time
60 sec
180 sec
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.
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EIGRP Convergence
(DUAL)
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 nexthop 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.
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10
20
RTX
Network
24
COST
10
RTY
FDDI
RTA
Serial
1
10
RTZ
100
100
RTA reaches Network 24 via:
Neighbor
RTX
RTY
RTZ
Computed Cost to 24
40
31
230
Report Distance to 24
30
21
220
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?
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10
20
RTX
Network
24
COST
10
RTY
FDDI
RTA
Serial
1
10
RTZ
100
Neighbor
RTX
RTY
RTZ
100
Computed Cost to 24
40
31
230
Report Distance to 24
30
21
220
Remember: RTA’s FD=31
Feasible successor =
1. It’s RD < RTA’s FD AND
2. Has the lowest computed cost of all other routes
DUAL calculates the feasible successor to be through RTX
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10
20
RTX
Network
24
COST
10
RTY
FDDI
RTA
Serial
1
10
RTZ
100
Neighbor
RTX
RTY
RTZ
100
Computed Cost to 24
40
31
230
Reported Distance to 24
30
21
220
Suppose RTX also goes down. Is there a feasible successor for RTA to Network 24?
Feasible successor =
1. It’s RD < RTA’s FD AND
2. Has the lowest computed cost of all other routes
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.
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Consider the output from the command ‘show ip eigrp
topology all’:
P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33
via 10.2.0.2 (2681856/2169856), Serial0
via 10.2.1.2 (2681856/2169856), Serial1
via 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
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Consider the output from ‘show ip eigrp topology all’:
P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33
via 10.2.0.2 (2681856/2169856), Serial0
via 10.2.1.2 (2681856/2169856), Serial1
via 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
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EIGRP
Operation
The 4 key steps to EIGRP operation are:
1.
building the neighbor table
2.
discovering routes
3.
choosing routes
4.
maintaining routes
Choose the routes based on these 5 factors:
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1.
bandwidth
2.
delay
3.
reliability
4.
load
5.
MTU (maximum transmission unit)
So, unless otherwise configured by an administrator,
bandwidth & delay are the only 2 factors that
determine EIGRP’s metric value.
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Configuring EIGRP
Configuring EIGRP for IP Networks
Router(config)# router eigrp autonomoussystem-number
Router(config-router)# network networknumber
network-number is the NETWORK address of
the interface of the router
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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).
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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 autosummary
Hence, with summarization turned off, EIGRP
routers will advertise subnets.
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Summarizing EIGRP routes
for IP
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.
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END
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