Download Advanced Networking Concepts & Troubleshooting

CCNA: Cisco Certified
Network Associate Study
Guide
CHAPTER 6:
Enhanced IGRP (EIGRP) and
Open Shortest Path First
(OSPF)
© Wiley Inc. 2006. All Rights Reserved.
The CCNA exam topics covered in this
chapter include the following:
Planning & Designing
• Select an appropriate routing protocol based on
user requirements
• Design a simple internetwork using Cisco
technology
Implementation & Operation
• Configure routing protocols
given user requirements
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What Is Enhanced IGRP
(EIGRP)?
IP Routing
Protocols
AppleTalk
Routing Protocol
IPX Routing
Protocols
IP Routing
Protocols
Enhanced
IGRP
AppleTalk
Routing Protocol
IPX Routing
Protocols
• Enhanced IGRP supports:
–
–
–
–
Rapid convergence
Reduced bandwidth usage
Multiple network-layer support
Uses Diffused Update Algorithm (DUAL) to select loop-free routes
and enable fast convergence
– Up to six unequal paths to a remote network (4 by default)
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Comparing EIGRP and IGRP
– Similar metric
– Same load balancing
– Improved convergence time
– Reduced network overhead
– Maximum hop count of 255 (100
default)
– EIGRP can differentiate between
internal and external routes
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EIGRP for IP
• No updates. Route updates sent only when a
change occurs – multicast on 224.0.0.10
• Hello messages sent to neighbors every 5
seconds (60 seconds in most WANs)
Enhanced IGRP
EIGRP
EIGRP
hello
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EIGRP Terminology
Neighbor Table—IP
Next Hop
Interface
Router
Topology Table—IP
Destination 1 Successor
Destination 1 Feasible Successor
Routing Table—IP
Destination 1 Successor
Note: A feasible successor is a backup route and stored in the Topology
table
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EIGRP Tables
• The neighbor table and topology table are
held in ram and are maintained through
the use of hello and update packets.
Enhanced IGRP
EIGRP
EIGRP
hello
To see all feasible successor routes known to a router, use
the show ip eigrp topology command
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Successor routes
• Successor route is used by EIGRP to forward
traffic to a destination
• A successor routes may be backed up by a
feasible successor route
• Successor routes are stored in both the topology
table and the routing table
Topology Table—IP
Destination 1 Successor
Destination 1 Feasible Successor
Routing Table—IP
Destination 1 Successor
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Choosing Routes
IP
IP
A
AppleTalk
B
19.2
T1
IPX
T1
IPX
T1
C
AppleTalk
D
• EIGRP uses a composite metric to pick the best
path: bandwidth and delay of the line
• EIGRP (and IGRP) can load balance across six
unequal cost paths to a remote network (4 by
default)
© Wiley Inc. 2006. All Rights Reserved.
Configuring EIGRP for IP
AS=10
A
10.110.1.0
B
Token
Ring
C
172.16.10.0
192.168.0.0
192.168.0.0
Enable EIGRP
Assign networks
Router(config)#router eigrp 10
Router(config-router)#network 10.0.0.0
Router(config-router)#network 172.16.0.0
If you use the same AS number for EIGRP as IGRP, EIGRP will
automatically redistribute IGRP into EIGRP
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Redistribution
Redistribution is translating one type of
routing protocol into another.
EIGRP
IGRP
Router B
Router D
Router A
Router C
IGRP and EIGRP translate automatically, as long as they are both using
the same AS number
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Route Path
Assuming all default parameters, which
route will RIP (v1 and v2) take, and which
route will EIGRP take?
T1
T1
56K
10BaseT
100BaseT
100BaseT
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Verifying Enhanced IGRP
Operation
•
Displays the neighbors discovered by
IP Enhanced IGRP
•
Displays the IP Enhanced IGRP
topology table
•
Displays current Enhanced IGRP
entries in the routing table
•
Displays the parameters and current
state of the active routing protocol
process
•
Displays the number of IP Enhanced
IGRP packets sent and received
Router# show ip eigrp neighbors
Router# show ip eigrp topology
Router# show ip route eigrp
Router# show ip protocols
Router# show ip eigrp traffic
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Show IP Route
P1R1#sh ip route
[output cut]
Gateway of last resort is not set
D 192.168.30.0/24 [90/2172] via 192.168.20.2,00:04:36, Serial0/0
C 192.168.10.0/24 is directly connected, FastEthernet0/0
D 192.168.40.0/24 [90/2681] via 192.168.20.2,00:04:36, Serial0/0
C 192.168.20.0/24 is directly connected, Serial0/0
D 192.168.50.0/24 [90/2707] via 192.168.20.2,00:04:35, Serial0/0
P1R1#
-D is for “Dual”
-[90/2172] is the administrative distance and cost of the route.
The cost of the route is a composite metric comprised from the
bandwidth and delay of the line
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Introducing OSPF
•
•
•
•
Open standard
Shortest path first (SPF) algorithm
Link-state routing protocol (vs. distance vector)
Can be used to route between AS’s
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OSPF Hierarchical Routing
•
•
•
•
Consists of areas and autonomous systems
Minimizes routing update traffic
Supports VLSM
Unlimited hop count
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Link State Vs. Distance Vector
Link State:
•
•
•
•
Provides common view of entire topology
Calculates shortest path
Utilizes event-triggered updates
Can be used to route between AS’s
Distance Vector:
•Exchanges routing tables with neighbors
•Utilizes frequent periodic updates
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Types of OSPF Routers
Area 1
Backbone Area 0
Area 2
ABR and
Backbone
Router Backbone/
Internal
Routers
Internal
Routers
Internal
Routers
ASBR and
ABR and
Backbone
Backbone
Router
Router
•External
AS
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Configuring Single Area OSPF
Router(config)#router ospf process-id
Defines OSPF as the IP routing protocol
Note: The process ID is locally significant and is needed
to identify a unique instance of an OSPF database
Router(config-router)#network address mask area area-id
Assigns networks to a specific OSPF area
© Wiley Inc. 2006. All Rights Reserved.
OSPF Example
R2
10.1.3.0
R1
R3
Area 0
10.5.5.0
10.1.2.0
10.1.1.0
hostname R3
hostname R2
router ospf 10
network 10.1.2.3 0.0.0.0 area 0
network 10.1.3.1 0.0.0.0 area 0
router ospf 20
network 10.0.0.0 0.255.255.255 area 0
hostname R1
router ospf 30
network 10.1.0.0 0.0.255.255 area 0
network 10.5.5.1 0.0.0.0 area 0
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Verifying the OSPF
Configuration
Router#show ip protocols
Verifies that OSPF is configured
Router#show ip route
Displays all the routes learned by the router
Router#show ip ospf interface
Displays area-ID and adjacency information
Router#show ip ospf neighbor
Displays OSPF-neighbor information on a per-interface basis
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OSFP Neighbors
• OSPF uses hello packets to create adjacencies
and maintain connectivity with neighbor
routers
• OSPF uses the multicast address 224.0.0.5
Hello?
224.0.0.5
•Hello packets provides dynamic neighbor discovery
•Hello Packets maintains neighbor relationships
•Hello packets and LSA’s from other routers help build and
maintain the topological database
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OSPF Terminology
• Neighbor
Neighbors
• Adjacency
ABR
DR
Adjacencies
Non-DR
Cost=6
BDR
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Router ID (RID)
Each router in OSPF needs to be uniquely identified to
properly arrange them in the Neighbor tables.
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Electing the DR and BDR
Multicast Hellos are sent and compared
Router with Highest Priority is Elected as DR
Router with 2nd Highest Priority is Elected as BDR
• OSPF sends Hellos which elect DRs and BDRs
• Router form adjacencies with DRs and BDRs in a multiaccess environment
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Configuring Loopback
Interfaces
Router ID (RID):
– Number by which the router is known to OSPF
– Default: The highest IP address on an active interface at the moment of
OSPF process startup
– Can be overridden by a loopback interface: Highest IP address of any
active loopback interface – also called a logical interface
© Wiley Inc. 2006. All Rights Reserved.
Interface Priorities
What is the default OSPF interface priority?
Router# show ip ospf interface ethernet0/0
Ethernet0 is up, line protocol is up
Internet Address 192.168.1.137/29, Area 4
Process ID 19, Router ID 192.168.1.137, Network Type BROADCAST,
Cost: 10 Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 192.168.1.137, Interface address 192.168.1.137
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 0, maximum is 0
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
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Ensuring your DR
What options can you configure that will ensure that R2
will be the DR of the LAN segment?
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Configuring Wildcards
If you want to advertise a partial octet
(subnet), you need to use wildcards.
– 0.0.0.0 means all octets match exactly
– 0.0.0.255 means that the first three match
exactly, but the last octet can be any value
After that, you must remember your
block sizes….
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Wildcard
The wildcard address is always one less than
the block size….
–
–
–
–
192.168.10.8/30 = 0.0.0.3
192.168.10.48/28 = 0.0.0.15
192.168.10.96/27 = 0.0.0.31
192.168.10.128/26 = 0.0.0.63
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Wildcard Configuration of the
Lab_B Router
•
•
•
Lab_A
E0: 192.168.30.1/24
S0: 172.16.10.5/30
•
•
•
•
Lab_B
E0: 192.168.40.1/24
S0: 192.168.10.10/30
S1: 192.168.10.6/30
•
•
•
Lab_C
E0: 192.168.50.1/24
S1: 172.16.10.9/30
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