CCNA3 module 3 EIGRP

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• CCNA3 module 3 EIGRP

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EIGRP

• Cisco proprietary, released in 1994
• Based on IGRP
• EIGRP is an advanced distance-vector routing
  protocol that relies on features commonly
  associated with link-state protocols. (sometimes
  called a hybrid routing protocol)
• Supports VLSM and CIDR
• Allows for multiple routed protocols

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EIGRP

• Uses Hello protocols to create and maintain
  neighbor relationships and to determine when a
  link is down. (Like link-state)
• Every 5 seconds, with a hold timer of 15 seconds
• Links less than T1 speed, Hellos are every 60
  seconds, hold timer of 180 seconds
• Partial routing updates in response to topology
  changes
• When a change in topology occurs, EIGRP does not
  flood updates like link-state protocols, but
  immediately sends those changes to its neighbors.
• Has speed and efficiency of routing updates like
  a link-state protocol, along with a topology
  database.

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EIGRP Benefits

• Rapid Convergence DUAL routing algorithm
• Efficient use of bandwidth
• partial, bounded updates only sent to routers
  that need the information not entire routing
  table
• small Hello packets to keep in touch with other
  routers minimal use of bandwidth
• Supports VLSM and CIDR
• Multiple network-layer support (multiprotocol)
• IP, IPX, and AppleTalk

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EIGRP and IGRP

• Automatically redistributes when using same AS
  number.
• Topology example.

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Metric calculation IGRP/EIGRP
metric K1 bandwidth ((K2 bandwidth) /
(256 load)) (K3 delay) K5/(reliability
K4)

• (with the following default constant values)
• Constant Value
• K1 1
• K2 0
• K3 1
• K4 0
• K5 0
• Notes
• k2 metric effects LOAD
• k4 and k5 effects RELIABILITY

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Metric Calculation

• Simplify the previous equation by applying the
  default constants

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Metric Calculation

• The metrics used by EIGRP in making routing
  decisions are (lower the metric the better)
• bandwidth
• delay
• load
• reliability
• By default, EIGRP uses only
• Bandwidth (carrying capacity)
• Delay (end-to-end travel time)

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Metric Calculation

• If these are the default
• bandwidth (default)
• delay (default)
• When are these used?
• load
• reliability
• Use show interface command to view the metrics
  used on a specific interface that is routing
  EIGRP.

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Metric Calculation show interfaces
Routergt show interfaces s1/0 Serial1/0 is up,
line protocol is up Hardware is QUICC Serial
Description Out to VERIO Internet address is
207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit,
DLY 20000 usec, rely 255/255, load 246/255
Encapsulation PPP, loopback not set Keepalive
set (10 sec) ltoutput omittedgt
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Metric Calculation Bandwidth

• Bandwidth
• Expressed in kilobits (show interface)
• This is a static number and used for metric
  calculations only.
• Does not necessarily reflect the actual bandwidth
  of the link.
• You can adjust the bandwidth metric on an
  interface using what command?
• What command restores the interface bandwidth to
  the original default?
• The default values
• What is the default bandwidth of serial
  interfaces on CISCO routers?

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Metric Calculation Delay

• Delay
• Like bandwidth, delay it is a static number.
• Expressed in microseconds, millionths of a second
  
• (Uses the Greek letter mu with an S, ?S, NOT
  ms which is millisecond or thousandths of a
  second)
• The default values
• What is the default delay of a Cisco serial
  interface?
• IGRP/EIGRP metric uses the sum of all of the
  delays of all of the outbound interfaces to the
  destination network.

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Metric Calculation Delay

• Changing the delay informational parameter
• The delay can be changed using
• Router(config-if) delay tens-of-?S
• (microseconds)
• Example of changing the delay on a serial
  interface to 30,000 microseconds
• Router(config-if) delay 3000
• To restore the 20,000 microsecond default value
  
• Router(config-if) no delay

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IGRP vs EIGRP Metric Calculation

• The difference
• IGRP metric is 24 bits long
• EIGRP metric is 32 bits long
• EIGRP metric is 256 times greater for the same
  route
• EIGRP allows for finer comparison of potential
  routes

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IGRP vs EIGRP Metric Calculation

• IGRP
• bandwidth (10,000,000 bandwidth)
• delay delay 10
• EIGRP
• bandwidth (10,000,000 bandwidth) 256
• delay (delay 10) 256
• Note The reference-bandwidth
• For both IGRP and EIGRP 107,
  (10,000,000/bandwidth), whereas with OSPF it
  was 108 (100,000,000/bandwidth)

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Metrics HOP COUNT

• EIGRP also imposes a maximum hop count of 224
• IGRP maximum hop count of 255
• RIP maximum hop count of 15

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EIGRP Configuration

• RTA(config) router eigrp AS
• RTA(config-router) network network
• RTA(config-router) eigrp log-neighbor-changes
• RTA(config-if)bandwidth kilobits

Enables logging of neighbor adjacency changes to
monitor stability help detect problems CISCO
recommends this command.
AS must be the same on all routers in the AS If
ASs are identical on a router running both IGRP
and EIGRP, routing tables are redistributed
automatically.
EIGRP assumes default if not set. If the link is
slower, router might not converge, routing
updates may be lost, or suboptimal path selection
may result.
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EIGRP tables

• Neighbor
• Topology
• Routing

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EIGRP Neighbor tables

• Lists adjacent routers
• One table for each routed protocol that EIGRP
  supports
• RTXshow ip eigrp neighbors
• IP-EIGRP neighbors for process 1
• H Address Interface Hold Uptime SRTT
  RTO Q Seq
• 
  (sec) (ms) Cnt Num
• 1 10.2.0.2 Se1 12 002739
  333 1998 0 10
• 0 10.1.0.1 Se0 14 011714
  40 240 0 27

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EIGRP Neighbor tables

• Fields in neighbor table
• Neighbor address (Address)
• Hold time (Hold Uptime)
• Smooth round-trip timer (SRTT)
• Queue count (Q Cnt)
• Sequence number (Seq No)

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DUAL calculating best paths

• DUAL (Diffusing Update Algorithm) allows
  routers involved in a topology change to
  synchronize at the same time, while not involving
  routers that are unaffected by the change
• (distance-vector algorithm)

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EIGRP Topology tables

• Contains all of the EIGRP routing tables in the
  autonomous system
• DUAL combines information supplied by neighbor
  and topology tables and calculates the lowest
  cost routes to each destination.
• EIGRP routers track changes and switch to
  alternate routes when necessary
• DUAL places this primary route, or successor
  route, information in the routing table

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EIGRP Topology tables

• Topology tables includes
• Feasible distance (FD) lowest calculated metric
  to each destination.
• Route source (via xxx.xxx.xxx.xxx) ID of router
  that originally advertised route
• Reported distance (RD) distance that an
  adjacent neighbor reports to specific destination
• Interface information interface through which
  the destination is reachable
• Route status
• passive (P) route is stable and ready for use
• Active (A) route is in the process of being
  recomputed by DUAL

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EIGRP Topology tables

• RTXshow ip eigrp topology
• IP-EIGRP Topology Table for process 100
• Codes P - Passive, A - Active, U - Update, Q -
  Query, R - Reply, r - Reply status
• P 200.10.3.0/24, 1 successors, FD is 2169856
• via Connected, Serial1
• via Redistributed (2169856/0)
• P 200.10.4.0/24, 1 successors, FD is 2169856
• via Connected, Serial0

RD
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EIGRP Topology tables

• Successor route that is selected as the primary
  route to use to reach a destination.
• DUAL identifies and places route in routing table
• There can be up to four successor routes for any
  particular route.
• Copy of successor is also placed in topology
  table
• EIGRP sorts the topology table so that the
  successor routes are at the top, followed by the
  feasible successors. Bottom of list may include
  routes that DUAL believes to be loops.

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EIGRP Topology tables

• Feasible Successor backup route
• Identified at same time as successor but kept
  only in the topology table
• May have multiple feasible successors but not
  mandatory to have any
• They are neighbors that are downstream (closer to
  the destination)
• Must have lower advertised cost than existing
  successor
• If feasible successor not identified, active
  status placed on route and query packets sent to
  all neighbors to recompute topology.

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Successor Feasible Successor
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Recomputation of Routes

• If route becomes unavailable and DUAL cannot find
  feasible successor.
• Neighbor routers are compelled to answer query
  for a loop-free path.
• If neighbor has no route, it responds so.
• Excess computation network instability
• To prevent convergence problems, DUAL always
  tries to find a feasible successor before
  resorting to recomputation

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Recomputation of Routes

• Stuck in Active routers
• one or more routers dont respond to query (180
  seconds) then routes placed in stuck in active
  state
• EIGRP then clears its table of neighbors that did
  not respond

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Route Tagging

• Routing Table
• Internal routes
• routes originating within the EIGRP AS
• External routes
• routes originating outside the EIGRP AS

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Routing Table Tagging

• RouterBshow ip route
• Codes C - connected, S - static, I - IGRP, R -
  RIP, M - mobile, B BGP, D - EIGRP, EX - EIGRP
  external, O - OSPF, IA - OSPF inter area, E1 -
  OSPF external type 1, E2 - OSPF external type 2,
  E EGP, i - IS-IS, L1 - IS-IS level-1, L2 -
  IS-IS level-2, - candidate default U - per-user
  static route
• Gateway of last resort is not set
• C 10.1.1.0 is directly connected, Serial0
• D 172.16.0.0 90/2681856 via 10.1.1.0,
  Serial0
• D EX 192.168.1.0 170/2681856 via 10.1.1.1,
  000004, Serial0
• External EIGRP routes are redistributed from IGRP
  networks

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Hellos RTM

• Hello Packets
• Sent every 5 seconds (high-bandwidth links) and
  every 60 seconds by default (low-bandwidth links)
• As long as routers receive hello packets route
  in passive state
• Reliable Transport Protocol (RTM)
• Layer 4 protocol
• Guarantees delivery of packets
• Allows EIGRP to multicast and unicast to
  different peers simultaneously

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DUAL FSM

• DUAL Finite-State Machine (DUAL FSM)
• Full name of DUAL technology
• Tracks routes advertised by neighbors and uses
  composite metric to compare them
• Guarantees each path is loop-free
• Inserts lowest-cost paths (successor routes) into
  routing table
• Neighbor Topology tables supply DUAL with route
  information to make decisions quickly

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DUAL FSM
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EIGRP Packets

• Hello Packets
• 5 second updates (T1/Point-to-Point link)
• Multicast on IP address 224.0.0.10
• Hold Time 3 times the Hello interval
• (15 seconds)
• Neighbor routers hello and dead intervals do not
  need to match with EIGRP (unlike OSPF)

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EIGRP Packets

• Acknowledgement
• Used by RTP to signal reliable exchange of
  information
• Unicast to specific host
• Update
• Discovery of new neighbor
• EIGRP router sends unicast to neighbor so that it
  can add to its topology table
• EIGRP router send multicast to all neighbors if
  topology change occurs

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EIGRP Packets

• Query Reply
• Query - Used to obtain specific information from
  one or all of its neighbors (multicast or
  unicast)
• Reply response to query (unicast)
• Used, for example, if DUAL places a route in
  active state and multicasts neighbors, searching
  for successor

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EIGRP Route Summarization
EIGRP automatically summarizes routes at the
classful boundary This may not be preferable,
especially if using VLSM To disable
auto-summarization Router(config-router)no
auto-summary Manual Summarization
command Router(config-if)ip summary-address
eigrp AS ip-address subnet-mask administrative
distance (configured on a per-interface basis)
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EIGRP Route Summarization
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Verifying EIGRP

• Show ip eigrp neighbors
• Show ip eigrp interfaces
• Show ip eigrp topology
• Show ip eigrp topology all-links
• Show ip eigrp traffic AS
• Debug eigrp fsm
• Debug eigrp packets

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RIP, IGRP, OSPF Troubleshooting

• Show debug commands
• Debug ip rip
• Debug ip igrp events
• Debug ip igrp transactions
• Debug ip ospf events
• Show ip route
• Show running-config
• Show ip protocols
• show ip ospf neighbor