Transcript Operating a Network Using Multiple IP Routing Protocols

Operating a
Network Using
Multiple IP Routing
Protocols
Implement an IPv4-Based Redistribution Solution
© 2009 Cisco Systems, Inc. All rights reserved.
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Complex Routing Scenarios
 Networks can be dispersed
– Politically
– Geographically
– As a result of acquisitions—company mergers
 Careful design and traffic optimization are required
– Redistribution
– Routing traffic filtering
– Summarization
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Using Multiple Routing Protocols
 Temporarily during conversion or migration only
 Application-specific protocols
– One size does not always fit all
 Political boundaries
– Groups that do not work well with others
 Mismatch between devices
– Multivendor interoperability
– Host-based routers
© 2009 Cisco Systems, Inc. All rights reserved.
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Using Multiple IP Routing Protocols
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Redistribution
 Routes learned by some other means are selectively redistributed
into a routing protocol from one of three sources:
– Another routing protocol
– Static routes
– Directly connected routes
 Routing loop prevention:
– Only routes used by the router itself are redistributed
 Double redistribution inside the same router is not allowed
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Redistributing Route Information
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Using Seed Metrics
 The initial, or seed, metric for a route is derived from the directly
connected router interface.
 Once a compatible metric is established, the metric will increase
in increments just like any other route.
R1#
router eigrp 110
network 10.0.0.0
redistribute rip
default-metric 1000 100 250 100 1500
 Use the default-metric command to establish the seed metric for
the route or specify the metric when redistributing.
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Default Seed Metrics
© 2009 Cisco Systems, Inc. All rights reserved.
Protocol
Default Seed Metric
RIP
Inifinity
EIGRP
Infinity
OSPF
20 for all except
BGP, which is 1
BGP
BGP metric is set to
IGP metric value
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Redistribution with Seed Metric
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One-Point Redistribution
 One-point redistribution
– One-way; default route or static routes needed
– Two-way
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One-Way and Two-Way Multipoint
Redistribution
 Multipoint redistribution
– One-way
– Two-way
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Redistribution Techniques
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Redistribution Implementation
Considerations
 Problems:
– Routing loop
 Suboptimal
path selection
– Incompatible
routing information
– Inconsistent
convergence time
 Solutions:
– Administrative
distance
– Route maps
– Distribution lists
– Manipulation of
metrics
© 2009 Cisco Systems, Inc. All rights reserved.
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One-Way Redistribution Issue
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One-Way Multipoint Redistribution Issue
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Two-Way Multipoint Redistribution Issue
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Summary
 Big, complex networks must be adjusted based on factors like
political borders, geographical borders, and mergers with other
companies. In such complex scenarios, running multiple IP
routing protocols is common.
 Using a routing protocol to advertise routes that are learned by
some other means, such as by another routing protocol, static
routes, or directly connected routes, is called redistribution.
 When a router advertises a link directly connected to one of its
interfaces, the initial, or seed, metric that is used is derived from
the characteristics of that interface. During redistribution the
default metric is used; when redistributing routes into RIP and
EIGRP, the default metric must be specified.
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Summary (Cont.)
 Redistribution can be one-point (one-way or two-way) or
multipoint (one-way or two-way). One-point redistribution, whether
one-way or two-way, is always safe, because it represents the
only exit from one routing protocol to another. In contrast,
multipoint redistribution is likely to introduce routing loops, so
careful design and configuration must be applied.
 The key issues that arise when you are using redistribution are
routing feedback (routing loops), incompatible routing information,
and inconsistent convergence time. Solutions to these issues
include correct design in terms of the administrative distance,
manipulation of metrics, and filtering using route maps and
distribution lists.
© 2009 Cisco Systems, Inc. All rights reserved.
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© 2009 Cisco Systems, Inc. All rights reserved.
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