Advanced EIGRP
Features in an
Enterprise Network
Implementing an EIGRP-Based Solution
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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Scalability in Large Networks
 Operating one large, flat
EIGRP network is not a scalable solution for to the following reasons:
– Large routing tables
– High memory requirements
– Large amount of routing traffic
© 2009 Cisco Systems, Inc. All rights reserved.
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Factors that Influence EIGRP Scalability
 Amount of routing information exchanged between peers
 Number of routers
 Depth of topology —the number of hops that information must travel to reach all routers
 Number of alternate paths through the network
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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EIGRP Design Challenges
 The number of neighboring routers on the common subnet
 The number of changes in the network
 The amount of EIGRP load on the WAN
 Every time a route disappears from the EIGRP process, DUAL computation is needed —resulting in high link utilization and CPU load
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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EIGRP Query Process
 Queries are sent when a route is lost and no feasible successor is available —route is in an active state
 Queries are sent to all neighboring routers on all interfaces except the interface of the successor
 If neighbors have the lost route information, they answer the query (and stop the query from spreading), otherwise queries are sent to their neighbors
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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EIGRP Query Process Stuck-in-Active
 The router must get replies to all its queries for a lost route to start calculating successor information
 If any reply to the query is lost or missing within 3 minutes:
– The route is SIA
– The router resets the neighbor relationship with the neighbor that fails to reply
© 2009 Cisco Systems, Inc. All rights reserved.
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Active Process Enhancement
Before:
 Router R1 resets the neighbor relationship to router R2 when the normal active timer expires.
After:
 An SIA query is used from router
R1.
 Router R3 ’s neighbor relationship is reset —problem on the link.
© 2009 Cisco Systems, Inc. All rights reserved.
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Updates and Queries Without an EIGRP
Stub
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Updates and Queries Using EIGRP Stub
 Router R1 should never use spoke routers to reach any network available through router R2.
 There is no reason to learn about or query for routes through spoke routers.
 Spoke routers should not be used for transit traffic —they can be configured as stubs.
© 2009 Cisco Systems, Inc. All rights reserved.
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EIGRP Stub
 The EIGRP stub routing feature does the following:
– Improves network stability
– Reduces resource utilization
– Simplifies remote router (spoke) configuration
 The feature is commonly used in hub-and-spoke topologies
– Each stub router reports its status to neighbors.
– Queries are not sent to the stub routers.
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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EIGRP Stub Configuration Planning
 Examine the topology and existing EIGRP configuration
 Define requirements
– Stub routers
– Redistribution
– Summarization
 Create an implementation plan
 Configure and verify the configuration
© 2009 Cisco Systems, Inc. All rights reserved.
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EIGRP Stub Options
 Stub options (default is with connected and summary )
– receive-only: prevents the stub from sending any type of route
– connected: permits the stub to send connected routes (may still need to redistribute)
– static: permits the stub to send static routes (must still redistribute)
– summary: permits the stub to send summary routes
– redistribute: permits the stub to send redistributed routes
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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Configuring eigrp stub connected
R2(config-router)# eigrp stub connected
 Router R2 will advertise to router R1
– 10.1.2.0/24
 Router R2 will not advertise to router R1
– 10.1.2.0/23
– 10.1.3.0/24
– 10.1.4.0/24
R2#
<output omitted> interface serial0
!
ip summary-address eigrp 10.1.2.0 255.255.254.0
ip route 10.1.4.0 255.255.255.0 10.1.1.10
!
router eigrp 110 redistribute static metric 1000 1 255 1 1500 network 10.2.2.2 0.0.0.3
network 10.1.2.0 0.0.0.255
eigrp stub connected
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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Configuring eigrp stub summary
R2(config-router)# eigrp stub summary
 Router R2 will advertise to router R1
– 10.1.2.0/23
 Router R2 will not advertise to router R1
– 10.1.2.0/24
– 10.1.3.0/24
– 10.1.4.0/24
© 2009 Cisco Systems, Inc. All rights reserved.
R2#
<output omitted> interface serial0
!
ip summary-address eigrp 10.1.2.0 255.255.254.0
ip route 10.1.4.0 255.255.255.0 10.1.1.10
!
router eigrp 110 redistribute static metric 1000 1 255 1 1500 network 10.2.2.2 0.0.0.3
network 10.1.2.0 0.0.0.255
eigrp stub summary
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Configuring eigrp stub static
R2(config-router)# eigrp stub static
 Router R2 will advertise to router R1
– 10.1.4.0/24
 Router R2 will not advertise to router R1
– 10.1.2.0/24
– 10.1.2.0/23
– 10.1.3.0/24
© 2009 Cisco Systems, Inc. All rights reserved.
R2#
<output omitted> interface serial0
!
ip summary-address eigrp 10.1.2.0 255.255.254.0
ip route 10.1.4.0 255.255.255.0 10.1.1.10
!
router eigrp 110 redistribute static metric 1000 1 255 1 1500 network 10.2.2.2 0.0.0.3
network 10.1.2.0 0.0.0.255
eigrp stub static
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Configuring eigrp stub receive-only
R2(config-router)# eigrp stub receive-only
 Router R2 will not advertise anything to router R1
 Router R1 needs to have a static route to the networks behind router R2 to reach them
R2#
<output omitted> interface serial0 ip summary-address eigrp 10.1.2.0 255.255.254.0
!
ip route 10.1.4.0 255.255.255.0 10.1.1.10
!
router eigrp 110 redistribute static metric 1000 1 255 1 1500 network 10.2.2.2 0.0.0.3
network 10.1.2.0 0.0.0.255
eigrp stub receive-only
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Configuring eigrp stub redistributed
R2(config-router)# eigrp stub redistributed
 Router R2 will advertise routes from RIP to router R1
R2#
<output omitted> router rip network 10.0.0.0
!
router eigrp 110 redistribute rip metric static 1000 1 255 1 1500 network 20.0.0.0
eigrp stub redistributed
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Summary
 Factors that affect network scalability include the amount of information exchanged between peers, the number of routers, the depth of the topology, and the number of alternate paths through the network.
 When a route is lost and no feasible successor is available, queries are sent to all neighboring routers on all interfaces.
 Once a route goes active and the query sequence is initiated, it can only come out of the active state and transition to the passive state when it receives a reply for every generated query. If the router does not receive a reply to all of the outstanding queries within 3 minutes (the default time), the route goes into the SIA state.
 The stub routing feature improves network stability, reduces resource utilization, and simplifies stub router configuration.
© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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© 2009 Cisco Systems, Inc. All rights reserved.
ROUTE v1.0
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