EIGRP to OSPF Migration Reference document for ArubaOS-CX ... · Enhanced Interior Gateway Routing Protocol EIGRP is an enhanced version of IGRP. The same distance vector technology

EIGRP to OSPF Migration Reference document for

ArubaOS-CX & ArubaOS-Switch

Published: Nov 2018

Rev: 1

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CONTENTS

Introduction ........................................................................................................................................................................................................................................... 1

About EIGRP .......................................................................................................................................................................................................................................... 1

Path Selection: ................................................................................................................................................................................................................................ 1

Summarization & VLSM .............................................................................................................................................................................................................. 1

Load Balancing & Load Sharing ............................................................................................................................................................................................... 1

Drawbacks of EIGRP ..................................................................................................................................................................................................................... 1

About OSPF .......................................................................................................................................................................................................................................... 2

OSPF Areas ..................................................................................................................................................................................................................................... 2

OSPF Interfaces ............................................................................................................................................................................................................................. 3

OSPF vs EIGRP ..................................................................................................................................................................................................................................... 3

Migration Strategy ............................................................................................................................................................................................................................. 4

Review ............................................................................................................................................................................................................................................... 4

Preparation ..................................................................................................................................................................................................................................... 4

Design Considerations ................................................................................................................................................................................................................ 4

Procedure ........................................................................................................................................................................................................................................ 4

Sample LAB .......................................................................................................................................................................................................................................... 5

Bill of Materials .............................................................................................................................................................................................................................. 5

Topology.......................................................................................................................................................................................................................................... 5

Configurations ............................................................................................................................................................................................................................... 5

1

EIGRP to OSPF Migration Reference Document for

ArubaOS-CX & ArubaOS-Switch

Introduction

This document provides guidance on how to migrate from Enhanced Interior Gateway Routing Protocol (EIGRP) and Open

Shortest Path First (OSPF), helps to consider the various aspects of both routing protocols and outlines the differences in brief

between EIGRP to OSPF.

EIGRP is an enhanced version of IGRP. IGRP and EIGRP are the proprietary protocols of Cisco, whereas OSPF developed by the

IETF as an open standard.

Compared with IGRP/EIGRP, OSPF features higher efficiency, better interoperability, and faster convergence, and supports more

protocol extensions.

Most IT infrastructures implement and maintain a best-of-breed, multi-vendor network infrastructures, instead of taking a single

vendor approach. OSPF is widely recommended to exchange routing information when there is a need to interop with multiple

vendors.

Network must be built on a hierarchical network architecture that allows for both flexibility and growth. In reality, network designs

vary depending on the size and requirements of the organizations. When choosing the routing protocol, must consider various

things like the type of network, complexity, scale, vendor compatibility, best path selection critieria, convergence time, routing

controls and protocol security etc

About EIGRP

Enhanced Interior Gateway Routing Protocol EIGRP is an enhanced version of IGRP. The same distance vector technology found in

IGRP is also used in EIGRP, and the underlying distance information remains unchanged

The convergence technology is based on Diffusing Update Algorithm (DUAL) is the algorithm used to obtain loop-free routes,

and provides fast convergence,

Path Selection:

EIGRP can choose best path based on multiple metrics as shown below:

Lowest bandwidth to this destination

Total delay

Reliability of path

Load on the end to end path

Maximum Transmission Unit (MTU)

Route Source (External vs Internal)

User can configure other metrics but it is not recommend

Summarization & VLSM

EIGRP supports Variable Length Subnet Mask, and helps to aggregate/summarize multiple subnets which helps to reduces routing

table size and save bandwidth.

Load Balancing & Load Sharing

Support load-balance over equal cost or unequal cost, but it’s not recommended by Cisco as it increases the work load and

consumes more routing resources to share the load.

Drawbacks of EIGRP

Scaling

Can’t set internal boundaries to controlling prefix summarization and database sizes

Have to use multiple EIGRP process ID’s to accomplish 5

2

SIA conditions

(SIA) stuck-in-active conditions, in which responses to queries are not heard within a certain time, causing neighbors to be

incorrectly flushed from the neighbor table, resulting in a severe network destabilization. SIA’s shouldn’t happen, but as EIGRP

networks grow, it could become an troubleshooting nightmare.

DUAL

Difficult to understand and difficult to troubleshoot during an outage.

Proprietary Protocol

Customers that have Cisco devices, they are faced with the realization that a proprietary protocol is a limiting factor in their

technology growth and not able to add in the best of breed devices to the network.

About OSPF

OSPF is an internal routing protocol based on link state developed by IETF. Supported by practically every routing vendor, as well

as the open source community.

OSPF routers rely on cost to compute the shortest path. The shortest path computation is done using Dijkstra’s algorithm.

The advantages of link state protocols provides a “view” of the entire network, preventing most routing loops, whereas distance

vector protocols route information is passed hop-by-hop through the network and a calculation is performed at each hop. Each

router is dependent on the router before it to perform its calculations correctly and then correctly pass along the results. When a

router advertises the prefixes it’s basically saying, “I know how to reach these destinations.” and because each distance vector

router knows only what its neighbors tell it, and has no “view” of that network beyond its neighbors.

The routers in an area cannot “see” past the ABR, and rely on the ABR to correctly tell them what prefixes it can reach, it’s the

behavior of distance vector and it is vulnerable to routing loops; To avoid loops by mandating a loop-free inter-area path, one

area can only reach other area through area 0.

OSPF Areas

A collections of routers grouped together called an Area, OSPF routers in an area don’t peer with routers in other areas except the

Area Border Routers (ABR). Areas help to build OSPF networks in a hierarchal maner which helps OSPF areas to scale as ABRs help

to avoid route computations from other areas. ABR’s help to summarize area wide routes simlifing advertisements to other

routers.

Its recommended to minimize the number of adjusencies(ADJ) in an area. In a campus network, optimal is 12 or fewer neighbors

of the same capability keeping device of similar performance in an area, also this helps to keep the number of OSPF shortest path

first (SPF) computations and database updates to a manageable amount.

Implementing multiple areas can be useful as it helps to create administrative boundaries in a network. Route

summarization/aggregation (replacing several small routes with one larger route) can only happen at OSPF area boundaries. Not

all routers need to know about every other route available in a network. Using OSPF areas, it’s possible to inject a default route

representing all routes outside of the local area.

Area types - Areas are logical groupings of hosts and networks, including their routers having interfaces connected to any of the

included networks. Each area maintains a separate link state database whose information may be summarized towards the rest of

the network by the connecting router

Backbone area known as area 0 that all OSPF areas must traverse to get to other OSPF areas.

Stub area - Area which does not receive external route advertisements

Not-so-stubby area – Can import autonomous system external routes and send them to other areas, but still cannot

receive AS-external routes from other areas

Totally Stud Area - External routes and other area destinations are no longer summarized or allowed

3

Transit area - two or more OSPF border routers and is used to transit traffic from one area to another

OSPF Interfaces

The two key OSPF network-types are broadcast and point-to-point

1. An OSPF broadcast interface is connected to a shared network, like Ethernet.

On broadcast links, there can be many different OSPF routers to on that network segment. To minimize the number

of neighbor relationships, OSPF elects a designated router (DR) also a backup designated router (BDR) whose job it

is to neighbor with all other OSPF routers on that segment and share everyone’s routes with everyone else

2. An OSPF point-to-point interface is connected to a link where there can only be a single OSPF router on either end, such

as a WAN link

On point-to-point links, — the two routers know they’re the only OSPF routers on the link and so they exchange

routes with each other..

OSPF vs EIGRP

OSPF EIGRP

Standards IETF Standard, implemented by mostly all venders

so it can interop

Cisco proprietary protocol, cannot interop

with any other vendor

Scope Widely deployed Fewer deployments

Algorithm SPF helps with fast convergence and calculates

loop-free routes

Diffusing update algorithm (DUAL):

Router may go into SIA state, when a

destination state unknown.

(SIA) stuck-in-active conditions, in which

responses to queries are not heard within a

certain time, causing neighbors to be

incorrectly flushed from the neighbor table,

resulting in a severe network destabilization.

SIA’s shouldn’t happen, but as EIGRP

networks grow, it could become a

troubleshooting nightmare.

Network topology Hierarchical topology support, helps with

manageability and scalability.

Entire Autonomous system seen as one

administrative domain, no support for

hierarchical topology support

Extensions OSPF-TE (Traffic Engineering Support)

Because OSPF like ISIS is based on TLV values, It

has support for extensions like MPLS-TE and

GMPLS

EIGRP does not support these

Convergence Speed OSPF supports BFD and becomes lightening quick

(as does ISIS).

EIGRP faster than OSPF when using it with

default settings.

Summarization Can’t set internal boundaries to controlling

prefix summarization and database sizes

4

Complexity & Controls Without a proper design, it can get very complex

to configure and manage

Using summarization and proper route filters can

really help to optimize the network

Simple to configure, but no controls or

limited controls

Migration Strategy

Review

Document the current routing configurations and table scale in use

Make note of CPU, Memory by each device

Capture the route-tables from each device for ref.

Make sure all the devices in the network support OSPF

Review the access routes, which are running at its capacity may not support two routing protocols simultaneously during the

migration

Which interfaces participating in which protocol

Redistributions and metrics, e.g. redistributed connected, static or other routing protocols

Which networks are summarized? Are they summarized automatically or at class boundaries?

Are the summarization defined on a specific interface, is so on which interface?

Is there any redistribution or route filters

Which routers announcing the default route and what’s the metric? Is there multiple routers sending the default route, which

one is preferred?

Preparation

Organize IP subnets to support summarization and to prepare for your area design.

reorganize the network in contiguous segments for a better design

Check your available bandwidth and bandwidth utilization, You must increase the bandwidth, if possible, and create quality of

service (QoS) policies

redistribution routes or, if possible, or filter out unwanted advertisements

Cleanup any unused protocols

Design Considerations

Design your areas depends on how you would like to control the incoming and outgoing routes

Backbone area – make sure all area’s around the backbone area

When the ABR announces only a default route, the area is a totally stubby area. If the ABR also announces some summary

routes, the area is a stubby area.

Standard (or normal) area where we do not hide networks, however, for convenience summarize the area’s routes with an

ABR.

Not so stubby areas (NSSAs) where they allow their routers to redistribute networks in the area if a router at the site can

announce a local default route for Internet access.

Consider factors that might cause downtime, possible disappearing a route from route-table

Consider the possibility of routing loops due to new summarizations

Procedure

Configure OSPF to operate in parallel with EIGRP until we confirm that OSPF fully functional and see all the required routes, if

both contribute the same route, the route with the lower administrative distance is preferred.

As EIGRP Administrative Distance (AD) is 90 and OSPF AD is 110 for intra-area, inter-area and external routes, OSPF route

table will not be effective until we change the EIGRP AD higher than OSPF or remove EIGRP

This strategy works only if all routers support both EIGRP and OSPF and be able to run them at the same time.

5

If the edge devices cannot support both protocols same time, prepare the configuration and remove & replace the new OSPF

config, which could impact a brief interruption to the networks behind the edge router.

Once the current devices migrated from EIGRP to OSPF, then you can introduce aruba devices in to the network

Sample LAB

Bill of Materials

1. Three EIGRP speaking devices

2. One ArubaOS-CX or ArubaOS-Switch [OSPF speking devices]

3. Two end-points (linux or windows machines)

Topology

As shown in the topology, Three Cisco switches are running on EIGRP and an Aruba switch with OSPF is being added to the

network. Here is the configuration steps helps to understand the migration from EIGRP to OSPF.

Configurations

STEP-1 (EIGRP AS IS)

SW01#show running-config

interface loopback11

ip address 11.1.1.1 255.255.255.255

!

interface vlan12

ip address 12.1.1.1 255.255.255.252

!

6

interface vlan13

ip address 13.1.1.1 255.255.255.252

!

ip routing

!

router eigrp 100

network 0.0.0.0 0.0.0.0

no auto-summary

!



ip address 22.1.1.1 255.255.255.255

!

interface vlan12

ip address 12.1.1.2 255.255.255.252

!

interface vlan23

ip address 23.1.1.2 255.255.255.252

!

ip routing

!

router eigrp 100

network 0.0.0.0 0.0.0.0

no auto-summary



ip address 33.1.1.1 255.255.255.255

!

interface vlan13

ip address 13.1.1.2 255.255.255.252

!

interface vlan23

ip address 23.1.1.1 255.255.255.252

!

router eigrp 100

network 0.0.0.0 0.0.0.0

no auto-summary

STEP-2 (Configure OSPF in background, EIGRP is still active)


router ospf 1

log-adjacency-changes

network 0.0.0.0 0.0.0.0 area 0

network 12.1.1.0 0.0.0.3 area 0

network 13.1.1.0 0.0.0.3 area 0


router ospf 1


network 22.1.1.0 0.0.0.0 area 0

network 12.1.1.0 0.0.0.3 area 0

network 23.1.1.0 0.0.0.3 area 0


router ospf 1


network 33.1.1.0 0.0.0.0 area 0

network 13.1.1.0 0.0.0.3 area 0

network 23.1.1.0 0.0.0.3 area 0

!

7

Confirm EIGRP still in action and OSPF is in background is able to see all routes as below

SW01#show ip route eigrp

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

a - application route

+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

23.0.0.0/30 is subnetted, 1 subnets

D 23.1.1.0 [90/3072] via 12.1.1.2, 00:03:04, Vlan12

23.1.1.0 [90/3072] via 13.1.1.2, 00:03:04, Vlan13


D 22.1.1.1 [90/130816] via 12.1.1.2, 00:03:04, Vlan12


D 33.1.1.1 [90/130816] via 13.1.1.2, 00:03:04, Vlan13













D 11.1.1.1 [90/130816] via 12.1.1.1, 00:13:15, Vlan12


D 33.1.1.1 [90/130816] via 23.1.1.1, 00:13:15, Vlan23


D 13.1.1.0 [90/3072] via 12.1.1.1, 00:13:15, Vlan12

13.1.1.0 [90/3072] via 23.1.1.1, 00:13:15, Vlan23













D 12.1.1.0 [90/3072] via 23.1.1.2, 00:15:05, Vlan23

12.1.1.0 [90/3072] via 13.1.1.1, 00:15:05, Vlan13


D 22.1.1.1 [90/130816] via 23.1.1.2, 00:15:05, Vlan23


8

D 11.1.1.1 [90/130816] via 13.1.1.1, 00:15:05, Vlan13

SW01#show ip route ospf











[NOTE - Same output shows in SW01,SW02 or SW03 as EIGRP has higher AD, but you can still see below, OSPF learned routes

in OSPF RIB which is ready to be installed if the AD is lower then EIGRP protocol]

SW1#sh ip ospf rib

OSPF Router with ID (11.1.1.1) (Process ID 1)

Base Topology (MTID 0)

OSPF local RIB

Codes: * - Best, > - Installed in global RIB

* 22.1.1.1/32, Intra, cost 2, area 0

via 12.1.1.2, Vlan12

* 33.1.1.1/32, Intra, cost 2, area 0

via 13.1.1.2, Vlan13

* 23.1.1.0/30, Intra, cost 2, area 0

via 12.1.1.2, Vlan12

via 13.1.1.2, Vlan13

SW02# sh ip ospf rib



OSPF local RIB


* 11.1.1.1/32, Intra, cost 2, area 0

via 12.1.1.1, Vlan12

* 33.1.1.1/32, Intra, cost 2, area 0

via 23.1.1.1, Vlan23

* 13.1.1.0/30, Intra, cost 2, area 0

via 12.1.1.1, Vlan12

via 23.1.1.1, Vlan13

!

SW03# sh ip ospf rib



OSPF local RIB


* 11.1.1.1/32, Intra, cost 2, area 0

via 13.1.1.1, Vlan13

* 22.1.1.1/32, Intra, cost 2, area 0

via 23.1.1.2, Vlan23

* 12.1.1.0/30, Intra, cost 2, area 0

via 13.1.1.1, Vlan13

via 23.1.1.2, Vlan23

STEP-3 (To get OSPF in action, remove EIGRP or higher the AD of EIGRP)

9

SW01#, SW02# and SW03#

configure t

no router eigrp 100

!

Confirm OSPF is able to see all routes as below













O 22.1.1.1 [110/2] via 12.1.1.2, 00:01:50, Vlan12


O 23.1.1.0 [110/2] via 12.1.1.2, 00:01:50, Vlan12

23.1.1.0 [110/2] via 13.1.1.2, 00:01:50, Vlan13


O 33.1.1.1 [110/2] via 13.1.1.2, 00:01:50, Vlan13













O 11.1.1.1 [110/2] via 12.1.1.1, 00:04:18, Vlan12


O 13.1.1.0 [110/2] via 12.1.1.1, 00:04:18, Vlan12

13.1.1.0 [110/2] via 23.1.1.1, 00:04:18, Vlan23


O 33.1.1.1 [110/2] via 23.1.1.1, 00:04:18, Vlan23












10


O 11.1.1.1 [110/2] via 13.1.1.1, 00:04:18, Vlan13


O 12.1.1.0 [110/2] via 13.1.1.1, 00:04:18, Vlan13

12.1.1.0 [110/2] via 23.1.1.2, 00:04:18, Vlan23


O 22.1.1.1 [110/2] via 23.1.1.2, 00:04:18, Vlan23

At this time only OSPF protocol in action, we can now add Aruba CX device to the topology as shown


interface vlan24

ip address 24.1.1.2 255.255.255.252

!

router ospf 1

network 24.1.1.0 0.0.0.3 area 0

!


interface vlan34

ip address 34.1.1.2 255.255.255.252

!

router ospf 1

network 34.1.1.0 0.0.0.3 area 0

!

Aruba CX device as SW04



ip address 44.1.1.1/32

ip ospf 1 area 0.0.0.0

interface vlan24



interface vlan34



router ospf 1

area 0.0.0.0

ArubaOS device as SW04


interface loopback 4

ip address 44.1.1.1

ip ospf 44.1.1.1 area backbone

exit

vlan 24

ip address 24.1.1.1 255.255.255.252

ip ospf area 0

interface vlan34

ip address 34.1.1.1 255.255.255.252

ip ospf area 0

ip routing

router ospf

enable

area backbone

Notice below outputs where SW4 is participating in OSPF routes.


3810M-SW4# sh ip route ospf

IP Route Entries

Destination Gateway VLAN Type Sub-Type Metric Dist.

------------------ --------------- ---- --------- ---------- ---------- -----

11.1.1.1/32 24.1.1.2 24 ospf IntraArea 3 110

12.1.1.0/30 24.1.1.2 24 ospf IntraArea 2 110

<output truncated>


SW02#sh ip route ospf

<output truncated>

11


O 44.1.1.1 [110/2] via 24.1.1.1, 00:00:46, Vlan24

Documents

EIGRP to OSPF Migration Reference document for ArubaOS-CX ... · Enhanced Interior Gateway Routing Protocol EIGRP is an enhanced version of IGRP. The same distance vector technology