08.OSPF Planning and Design Process

7/28/2019 08.OSPF Planning and Design Process

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Cisco CCNP ROUTE TrainingInstructor: Joe Rinehart, CCIE #14256

OSPF Planning andDesign Process

Cisco CCNP ROUTE Training

OSPF Planning and Design Process

In This Lesson:

Unique Characteristics of OSPF

When OSPF is the Best Design Choice

OSPF Planning Methodology

Verification Plan for Implementation

Implementation Steps

Transitioning to OSPF from Another Protocol




1. Brief History of OSPF

2. Link-State Protocol Characteristics

3. Unique OSPF Features


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Brief History of OSPFNeed for More Robust IGP

IETF Formed OSPF Working Group in1988 to Replace RIP:

Network size limitations

Inability to choose higher bandwidthinterfaces/links

Derived from Several Sources

Bolt, Beranek, and Newman's (BBN)SPF algorithm for ARPANET (1978)

Radia Perlmans research on faulttolerant broadcast of routing data(1988)

BBNs Area Routing Work (1986)

Early Version of OSI IS-IS ProtocolJohn Moy, OSPF:Anatomy of an Internet Routing Protocol(Reading Mass: Addison-Wesley, 1998)

1987

1989

1991

1993

1995

1997

OSPF Working

Group Formed

OSPF V1PublishedFirst OSPF

Interoperability

Testing

OSPF Demo at

Interop 91

OSPF V2

Published

OSPF

Recommended

IGP

OSPF V2

UpdatedInternet Adopts

CIDRCrypto

Added

OSPF V2

Updated



Link-State Protocol Characteristics

Formal Neighbor Relationships

Hello packets sent for neighbor discoveryand maintenance

Database synchronization and exchange

Active tracking of neighbor state

Link State (Topology) Database

Constructed of information about activepaths (links) in the network

All routers contain copies of the database

Update Process

Once database is built only changes sent When there is a change it is flooded

Dijkstra algorithm used for calculation

Network 1 Network 2

Network 3 Network 4

XLink

Outage

R1

R3

R2

R4

R3 LSA



Link-State Protocol Characteristics

Rapid Convergence

Link-state database and path calculationprocess is rapid and very efficient

Loop avoidance inherent in the protocol

Higher CPU and memory utilization

Complexity

Greater amount of effort required inplanning and design process

Configuration requires more work

Vastly greater depth in routing logic andcomputation process

Network 1 Network 2

Network 3 Network 4

XLink

Outage

R1

R3

R2

R4

R3 LSA


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Unique OSPF Features

Formal Hierarchy

Ability to segment the network intomultiple section called areas

Area 0 (Backbone) is required and allother areas must directly connect to it

Flooding and route calculation is

restricted within each area

Route Summarization

Support for aggregation/supernetting

Configurable on a per-area basis

Industry Standard Protocol

Open designates OSPF as standard

Implemented by every equipment vendor

Network 1 Network 2

Network 3 Network 4

XLink

Outage

R1

R3

R2

R4

R3 LSA



Unique OSPF Features

Cost as Basis for Route Selection

Bandwidth of interface assigned a cost

Lowest cumulative cost to destinationnetwork makes for best route

Different Network Types Supported

Broadcast (e.g., Ethernet LAN)

Non-Broadcast

Point-to-Point

Point to Multipoint (Non)Broadcast

Neighbor Types

Designated Router (DR): Single peer onbroadcast network

Backup DR: Secondary peer

Network 1 Network 2

Network 3 Network 4

XLink

Outage

R1

R3

R2

R4

R3 LSA




1. In Multi-Vendor Routing Environment

2. For Scalability in Large Networks

3. Design Principles for OSPF


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In Multi-Vendor Routing Environment

Routing and/or Layer 3 Switches Can Befrom ANY Equipment Manufacturer

OSPF V2 (IPV4) and V3 (IPV6)assumed

Open standard

Vendor Support List (Partial)

Cisco

Avaya

Juniper

HP

Adtran

Enterasys




For Scalability in Large Networks

OSPF can experience stuck-in-activeconditions in very large topologies

Link State Database synchronization and

flooding behavior limited to areas

Address summarization in areas

Fewer SPF calculations using areas




Design Principles for OSPF

Multi-Access Network Peering

Routers establish one peeringrelationship (DR/BDR)

Select and configure DR/BDR usingthe priority command

Serial Interface Bandwidth

OSPF also assumes 1.544 Mbps forany serial interface

Use the bandwidth command to setthe actual value

Remember that frame-relay isinherently a non-broadcast medium


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Limit Number of Routers per Area

Older documentation recommends 50

Depends on a variety of factors:

Type of area (stub, NSSA, etc.)

Number of external LSAs

How well other areas are/can besummarized

CPU and memory available on thedevices

Media type (LAN/Frame-Relay,

etc.)





Limit Number of Area Border Routers

ABRs keep separate databases foreach area connected

Also depends on a variety of factors

Can be avoided by allocatingconnectivity to additional devices

Goal is not to overload the ABR

Summarize Addressing When Possible

Design and use IP addressing that

can be summarizedDeploy address summarization

whenever practical and possible





Carefully Choose Area Designs

Avoid placing devices in area 0 unlesscritical to overall network operations

Use redundant links betweenbackbone routers whenever possible

Maintain consistency in designation oflabeling for areas

Create a template for areas

Avoid the use of virtual-links

Try to anticipate growth in the designprocess


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1. General Network Design Principles

2. High Level Design

3. Pilot/Proof of Concept Testing

4. Review and Verification Process




General Network Design Principles

Start with REQUIREMENTS

Know what the expectations are

Be able to clearly explain theexpected outcomes

Gather all of the facts

Perform a physical site inspection

Account for power, cabling, anddevice placement

Know the availability and timeline of

WAN circuitsAccount for any existing devices that

require support




General Network Design Principles

Document allASSUMPTIONS

Financial (capital budget/operationalcosts)

Who is responsible for what

Expected time for design,implementation and testing

Other people/organizations involved

Ask questions for confirmation

Get everything in writing and signedas confirmation

Develop contingency plans

Develop and stick to a project plan


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High Level Design

Create High-Level Diagram(s)

Site Locations

Proposed equipment

VLAN/LAN IP Addressing

Wide Area Connection Links

Routing protocol domains

Develop a Bill of Materials (BOM)

Equipment (type and quantity)

Lead time/delivery dates

SMARTnet Maintenance

Staging logistics




High Level Design

System-Wide IP Addressing Allocation

Subnet, mask(s), equipment IPs

Consistency in addressing

Database of addresses and locations

Reserved and unused rangesdocumented

Ability to summarize contiguousranges of addresses

Track usage/decommissioning of

addresses within the pool(s) Turn the high-level plan into detailed

plans after approvals




Pilot/Proof of Concept Testing

When Implementing New Technologies, aPilot or Proof of Concept Trial is Advisable

Technology: Wireless, Unified

Communications, etc.

Devices: New models/types of LANswitches, routers, etc.

Acquisition: Business merger,telecommuter program, etc.

Protocol: Change of routingprotocol, etc.

Process: Changes the way thecompany is doing business (e.g.,replacing card payment systems)


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Pilot/Proof of Concept Testing

Map Out a Testing Environment thatRepresents the Larger Project

Scope: Subset of the number andtype(s) of sites

Devices: Same type(s) of devices to

be used in larger implementation

Staging: Create a lab-centricminiature version of the network

Testing Plan: Create a plan that willtest the limits and outcomes

Reporting: Codify results andconclusions for use in the largerimplementation (lessons learned)




Review and Verification Process

Involve as many competent people in theprocess of reviewing your designs anddocumentation

Peers: Those in your department

Experts: Individuals whose skills andexperience are greater than your own

Critics: Carefully chosen peoplewhose evaluation is likely to beaccurate

Superiors: Direct supervisor or

department heads

Others: Additional reviewers asneeded




1. Detailed Project Plan

2. Device-Specific Configurations

3. Verification Steps


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Detailed Project Plan

Basic Document Format

Identification of stakeholders

Identification of roles andresponsibilities

Timelines and milestones

Communication plan

Account for power, cabling, anddevice placement

Implementation plan(s)

Expected outcomes

Criteria for completion




Device-Specific Configurations

Routers/Layer 3 Devices

Hostnames (adhering to standards)

Interface configurations

Security configurations

EIGRP Routing configuration elements

Usernames/Passwords/TACACS

Network Time Protocol

SNMP/Syslog

WAN configurations

Device access

Advanced configurations




Device-Specific Configurations

Layer 2/3 Switches

Hostnames (adhering to standards)

SVI Interface configurations

Security configurations

Usernames/Passwords/TACACS

Network Time Protocol

SNMP/Syslog

VLAN configurations

Device access

Advanced configurations


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Verification Steps

Commands Verifying Configuration(s)

General Connectivity/Functionality

show ip interface brief

show cdp neighbors

show environment all

show diag

show inventory

OSPF Routing

show ip protocols

show ip ospf interfaces

show ip ospf neighbor

show ip ospf database

show ip route ospf



Verification Steps

Commands Verifying Configuration(s)

General Connectivity/Functionality

debug ip packet

debug interface

OSPF Routing

debug ip ospf adjacency

debug ip ospf events

debug ip ospf hello

debug ip ospf spf

debug ip ospf lsa-generation

debug ip ospf packet

debug ip ospf flood




1. In a New (Greenfield) Environment

2. In an Existing Network


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In a New (Greenfield) Environment

Assumptions

Not necessarily a first-time networkinstallation

May involve new equipment and/ornew telecommunications circuits

Probably maintaining identical LANaddressing

Other routing protocols in use in all orpart of the existing network

Static routing

EIGRP

RIP





Transition Process

Stage new equipment with OSPF

Connect only a small test network foranalysis purposes

Have full configuration available forday of transition

Have full testing plan codified

Schedule outage window after hours

Migrate area 0 First

Disconnect old devices and swap withnew OSPF devices

Execute test plan and certify network




In an Existing Network

Assumptions

Existing equipment will host OSPF

No new circuits or IP addressing

Involves a hot cut to implement

Requires several key elements:

Transition plan

Testing plan

Roll-back plan in the event ofissues


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Transition Process

Configure OSPF with a higheradministrative distance (suggesteddistance of224)

Ability to establish OSPF neighbor

relationships and peering

May stage dummy IP addresses toserve as testing points

Schedule an outage window afterhours

At transition time set administrativedistance back to 110

Execute test plan and certify network



Key Terms You Should Know

Link-State Class of Interior Gateway Protocol that relies on alldevices having an identical understanding of the network (links)

DR/BDR Designated Router/Backup Designated Router, theprimary/secondary devices that all devices on a multi-access

establish a neighbor relationship with

Area In OSPF, a partitioned section of the network in which allrouters maintain an identical copy of the link state database

Area 0Also referred to as the backbone area, the OSPF arearequired area through which all traffic must transit

Roll-Back Plan Contingency plan for restoring the network toits original state following an unsuccessful transition attempt

Greenfield Term used to describe installation of a brand-newnetwork infrastructure in a given location



What We Covered




Verification Plan for Implementation



08.OSPF Planning and Design Process

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