Download Module 3 - IT, Sligo

CCNA 3 v3.1 Module 3
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CCNA 3 Module 3
Enhanced Interior Gateway Routing Protocol (EIGRP)
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EIGRP
• Cisco-proprietary routing protocol
Based on Interior Gateway Routing Protocol (IGRP)
• How does EIGRP improve on IGRP
Supports classless interdomain routing (CIDR)
Network designers can maximize address space
Variable-length subnet mask (VLSM)
Fast convergence times
Improved scalability
Superior handling of routing loops.
• Hybrid routing protocol combining
distance vector and link-state algorithms
• An ideal choice for large, multi-protocol
networks built primarily on Cisco routers
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EIGRP Versus IGRP
• Compatibility mode
IGRP and EIGRP are interoperable
EIGRP offers multiprotocol support
• Metric calculation (Bandwidth + Delay)
EIGRP - 32 bit metric for bandwidth and delay
IGRP – 24 bit metric for bandwidth and delay
IGRP Bandwidth = 1000000/bandwidth Kbps
EIGRP Bandwidth = (1000000/bandwidth Kbps)*256
IGRP Delay = delay/10
EIGRP Delay = (delay / 10) * 256
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• Hop count
IGRP maximum hop is 255
EIGRP maximum hop is 224
• Automatic protocol redistribution
IGRP and EIGRP can share routes if both have the same
autonomous system number
• Route tagging
EIGRP tags routes learned from IGRP as external
IGRP does not tag routes
• Holddown timers
EIGRP 180
IGRP 280
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D = EIGRP routing
EX = External route
I = IGRP routing
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EIGRP Terminology and Concepts
• Holds route and topology information in
RAM
• EIGRP Tables
Neighbor Table
Topology Table
Routing Table
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Neighbor
Table
• Lists adjacent
routers
• Similar to OSPFs adjacency database
• One for each protocol EIGRP supports
• Neighbors send hello packets
Containing holddown timer
If neighbor does not send another hello packet before
holddown timer expires the neighbor is unreachable or
unoperational
When the hold time expires
Diffusing Update Algorithm (DUAL) (EIGRP distance vector
algorithm) recalculate the new topology
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NB
• Fields in the neighbor table
Neighbor Address
Layer 3 address of neighbor router
Hold time
Time to wait before considering link down
Smooth Round Trip timer
Average time to send and receive packet
Queue count
Amount of IEGRP packets in queue
Sequence number
Number of last packet received from neighbor
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Topology Table
• All EIGRP routing tables in the AS
• DUAL takes information from neighbor table and
topology table and calculates the lowest cost
routes to each destination
• Successor
Neighbor router that is the next hop in a least cost, loopfree path to a destination
• All learned routes to a destination are maintained in
the topology table
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FD/RD
Admin distance
Feasible Distance (e.g., 90) - the lowest metric (cost) to each destination
Route Source (via 200.10.10.10) – router that originally advertised that route
Reported Distance (e.g., 2195456) – cost of route as advertised by the neighbor router
Interface information – The interface through which the destination is reachable
Route status – passive (P) the route is stable and ready for use
active (A) the route is in the process of being recomputed by DUAL
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EIGRP Routing Table
• Holds the best routes to a destination
• Routing table for each network protocol.
• A successor is a route selected as the primary route to use to
reach a destination
The preferred root to the destination
DUAL calculates this using neighbor and topology tables
It is placed in the routing table
A copy if it is placed in the topology table
Up to 4 successor routes for any particular route
equal or unequal cost
identified as the best loop-free paths to a given destination
• A feasible successor (FS) is a backup route
only kept in the topology table
not mandatory
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EIGRP Design Features
• Rapid convergence
DUAL guarantees loop-free operation at every instant throughout a
route computation allowing all routers involved in a topology
change to synchronize at the same time
• Efficient use of bandwidth
partial, incremental updates to routers that need the information
(bounded updates)
Hello packets keep routers in touch with each other
• Support for variable-length subnet mask (VLSM) and classless
interdomain routing (CIDR)
• Multiple network-layer support
supports IP, IPX, and AppleTalk through protocol-dependent
modules (PDMs).
• Independence from routed protocols.
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1. Neighbor discovery and recovery
EIGRP
Technologies
Form adjacencies by sending Hello packet every five seconds
This allows EIGRP to
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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Reliable Transport Protocol (RTP)
Transport-layer protocol guarantee ordered delivery of EIGRP packets
to all neighbors – used for reliability of transmission
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DUAL finite-state machine algorithm
Contains all the logic used to calculate and compare routes in an
EIGRP network
DUAL tracks all the routes advertised by neighbors
DUAL also guarantees that each path is loop free
DUAL inserts lowest cost paths into the routing table (successor
routes)
DUAL places a copy of successor routes in the topology
table(feasability successor)
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Protocol-dependent modules
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EIGRP Data Strucutre
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EIGRP Packet Types
Hello - discover, verify, rediscover neighbor routers
Sent unreliably – no acknowledgement needed
EIGRP routers send hellos to the multicast IP address
224.0.0.10
Default hello interval depends on the bandwidth of
the interface
Acknowledgment - indicate receipt of any EIGRP packet
during a reliable exchange
Update - unicast update packets sent to new neighbor so that
it can add to its topology table
Query – to find specific information about a router
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EIGRP Configuration
• router(config)#router eigrp autonomous-systemnumber
AS-number identifies all routers within the internetwork
• router(config-router)#network network-number
Specify all connected networks only
• router(config-if)#bandwidth kilobits
Set the bandwidth for the serial link
• router(config-if)#eigrp log-neighbor-changes
enables the logging of neighbor adjacency changes to
monitor the stability of the routing system and to help
detect problems
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• Why is it necessary to set the bandwidth
n/w may be unable to converge if bandwidth setting
does not match actual bandwidth
A suboptimal route may be chosen as the best path to a
destination if the bandwidth setting is higher than the
actual bandwidth
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Configuring EIGRP summarization
• EIGRP automatically summarizes routes at the classful
boundary
summarization keeps routing tables as compact as possible
• router(config-router)#no auto-summary
Turns off route summarization when manually configuring
• To manually configure a summary address
router(config-if)#ip summary-address eigrp autonomoussystem-number ip-address mask administrativedistance
• Administrative distance for EIGRP summary
routes
Default is 5
Can be configured to between 1 and 255
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• It is necessary to configure the bandwidth
setting on an EIGRP interface rather than
leaving it at the default setting because
A suboptimal route may be chosen as the best
path to a destination if the bandwidth setting is
higher than the actual bandwidth of the link
The network may be unable to converge if the
bandwidth setting does not match the actual
bandwidth of the link.
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Verifying EIGRP
• Show ip eigrp neighbors
Displays eigrp neighbor table
• Show ip eigrp interfaces
Displys eigrp information for each interface
• Show ip eigrp topology [keyword]
Displays feasible successors
Keywords - Active, pending, zero successor
• Show ip eigrp all-links
Displays all routes not just feasable successors
• Show ip eigrp traffic
Displays the number of eigrp packets sent/recieved
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Troubleshooting RIP
• RIP Problems
Most common problem RIP V1prevent variable-length subnet mask
(VLSM) being advertised.
Layer 1 or Layer 2 connectivity issues exist.
Mismatched RIP v1 and RIP v2 routing configurations exist.
Network statements are missing or incorrectly assigned.
The outgoing interface is down.
The advertised network interface is down.
• Troubleshooting
show ip protocols displays current state of the active routing
protocol process
debug ip rip Display information on RIP routing transactions
Turn this off using no debug ip rip, no debug all, or undebug all
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Troubleshooting IGRP
• IGRP Problem checks
Layer 1 or Layer 2 connectivity issues exist.
Autonomous system numbers on IGRP routers are
mismatched.
Network statements are missing or incorrectly assigned.
The outgoing interface is down.
The advertised network interface is down.
• To debug IGRP
debug ip igrp transactions [host ip address]
to view IGRP transaction information
debug ip igrp events [host ip address]
to view routing update information
To turn off debugging, use the no debug ip igrp command.
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Troubleshooting EIGRP
• Possible reasons why EIGRP is not working correctly
Layer 1 or Layer 2 connectivity issues exist
most common reasons for a missing neighbor is failure on the actual
link
Autonomous system numbers on EIGRP routers are mismatched.
The link may be congested or down.
The outgoing interface is down.
The advertised network interface is down.
Auto-summarization is enabled on routers with discontiguous subnets.
Use no auto-summary to disable automatic network summarization
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• Show ip route eigrp
Displays current eigrp entries in routing table
• Show ip protocols
Displays EIGRP AS number, filtering and
redistribution numbers, neighbors
• Show ip eigrp traffic
Displays packets sent and recieved
Static on hello, update, query, replies, acks
• Eigrp log-neighbor-changes
Displays a history of when and why neighbors
have been reset
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Troubleshooting OSPF
• Show ip ospf neighbor
Displays OSPF neighbor one each interface
Displays routes known to the router and how they were
learned
• Show ip ospf interface
Displays timer intervals, neighbor adjacencies
Determines if OSPF is enabled on each interface
• Debug ip ospf events
Displays Adjacencies, Flooding information, Designated router
selection, Shortest path first (SPF) calculation
• Debug ip ospf packets
Displays information about OSPF packets received
• No debug ip ospf packets
Turns off debugging
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