IOS_Interior_Routing_Protocols(2).pdf

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Unicast Routing Protocols Comparison

OSPF

Router Roles

Internal Router

All interfaces reside within the same area

Backbone Router

A router with at least one interface in area 0

Area Border Router (ABR)

Connects two or more areas

AS Boundary Router (ASBR)

Connects to additional routing domains

(redistribution to or from other protocols)

Metric Formula

OSPF Configuration

RIP

EIGRP

OSPF

IS-IS

BGP

cost = reference-bandwidth

link speed

! Create an OSPF process

[ipv6] router ospf process-ID

Type

Distance Vector

Link State

Path Vector

OSPFv2 Link State Advertisements

Router Link (Type 1)

Lists neighboring routers and the cost to each;

flooded within an area

Network Link (Type 2)

Generated by a DR; lists all routers on an

adjacent segment; flooded within an area

Network Summary (Type 3)

Generated by an ABR; advertises routes

between areas

ASBR Summary (Type 4)

Injected by an ABR into the backbone to

advertise the presence of an ASBR in a non-

backbone area

External Link (Type 5)

Generated by an ASBR and flooded throughout

the AS to advertise a route external to OSPF

Adjacency States

Algorithm

Bellman-Ford

DUAL

Dijkstra

Path Selection

! Specify a router ID formatted as IPv4 dotted-decimal

router-id router-ID

Down

ExStart

Admin Distance

120

90/170 (external)/5 (summary)

110

115

20/200 (IBGP)

Attempt

Exchange

! Modify the default reference bandwidth

auto-cost reference-bandwidth speed-in-mbps

Standard

RFCs 2080, 2453

Cisco proprietary

RFCs 2328, 5340

ISO 10589, RFC 1142

RFC 4271

Init

Supported Protocols

IPv4, IPv6

IPv4, IPv6, IPX, Appletalk

IPv4, IPv6

IPv4, IPv6, CLNP

IPv4, IPv6

2-Way

Full

! Assign interfaces to areas by network (OSPFv2)

network IPv4-address wildcard-mask area area

Transport

UDP/520

IP/88

IP/89

Layer 2

TCP/179

Message Types

Area Types

Authentication Plain, MD5

MD5

Plain, MD5, AH (v3) Plain, MD5

MD5

! Identify neighbors for NBMA links (OSPFv2)

neighbor IPv4-address [cost 1-65535]

Hello

DB Descr.

LS Update

LS Ack

Standard Area

Default OSPF area type

Stub Area

External link (type 5) LSAs are replaced with

a single default route

Totally Stubby Area

Type 3, 4, and 5 LSAs are replaced with a

default route

Not-So-Stubby Area (NSSA)

A stub area containing an ASBR; type 5 LSAs

are converted to type 7 within the area

Multicast Address 224.0.0.9

224.0.0.10

224.0.0.5-6

N/A

! Configure summaries on area border routers

area area range { IPv4-address subnet-mask | IPv6-prefix }

LS Request

RIP

Terminology

Split-Horizon

Mitigates routing loops by ensuring a

route is never advertised back to the

neighbor from which it was learned

Poison Reverse

Learned routes are advertised back to

their originator as explicitly invalid

RIP Configuration

DR/BDR Election

! Summarize external routes (ASBRs only)

summary-address IPv4-address subnet-mask [not-advertise]

summary-prefix IPv6-prefix [not-advertise]

! Enable RIPv2 IPv4 routing

router rip

version 2

Ğ The DR serves as a common

point for all adjacencies on a

multiaccess segment

RIP Implementations

RIPv1

Original RIP implementation, limited to

classful routing (obsolete)

! Originate a default route

default-information originate [always]

Group Membership (Type 6)

Used by Multicast OSPF; unsupported by IOS

! Disable RIPv2 automatic summarization

no auto-summary

Ğ The BDR also maintains

adjacencies with all routers in

case the DR fails

Ğ Does not occur on point-to-

point or multipoint links

Ğ Default priority (0-255) is 1;

highest priority wins; 0 cannot

be elected

Ğ DR preemption will not occur

unless the current DR is reset

RIPv2

Introduced support for classless routing,

triggered updates, and multicast

announcements (RFC 2453)

NSSA External Link (Type 7)

Generated by an ASBR in a not-so-stubby area;

converted into a type 5 LSA by the ABR when

leaving the area

! Designate stub, totally stubby, or not-so-stubby areas

area area { stub | nssa } [no-summary]

! Designate RIPv2 interfaces by network

network IPv4-network

Troubleshooting

External Route Types

! Create a virtual link

area area virtual-link router-ID

! Identify unicast-only neighbors

neighbor IP-address

Considers the cost to the advertising ASBR

plus the external cost of the route

E2 (Default)

The external cost of a route as seen by the

ASBR; internal OSPF cost is not considered

show ip[v6] protocols

show ip[v6] rip database

RIPng (RIP Next Generation)

Extends RIPv2 to support IPv6 routing

(RFC 2080); functions very similarly to

RIPv2 and is subsequently as limited

OSPFv3 Link State Advertisements

! Originate a default route

default-information originate

interface type number

debug ip rip { database | events }

debug ipv6 rip [interface]

Name

v2 Equiv.

0x2001

0x2002

Router LSA

Network LSA

Type 1

Type 2

! Enable OSPF on the interface

ip[v6] ospf process-ID area area

! Designate passive interfaces

passive-interface {interface | default}

RIP Configuration

Virtual Links

Ğ Tunnel formed to join two

areas across an intermediate

Ğ Both end routers must share

a common non-stub area

Ğ At least one end must reside

in area 0

! Identify neighbors for NBMA links (OSPFv3)

ipv6 ospf neighbor IPv6-address

0x2003

0x2004

Inter-area prefix LSA

Inter-area router LSA

Type 3

Type 4

Troubleshooting

! Modify equal-cost load balancing

maximum-paths 1-16

interface type number

show ip[v6] ospf [process] interface

! Set interface cost manually

ip[v6] ospf cost 1-65535

! Enable RIPng on the interface

ipv6 rip name enable

0x4005

AS-external LSA

Type 5

show ip[v6] ospf [process] neighbor

! Modify timers

timers basic update invalid hold flush

0x2006 Group membership LSA

Type 6

show ip[v6] ospf border-routers

! Configure DR election priority

ip[v6] ospf priority 0-255

! Configure manual route summarization

ip summary-address rip IPv4-address subnet-mask

ipv6 rip name summary-address IPv6-prefix

0x2007

0x0008

Type-7 LSA

Link LSA

Type 7

N/A

show ip[v6] ospf database [LSA-type]

! Enable RIPng IPv6 routing

ipv6 router rip name

show ip[v6] ospf virtual-links

Ğ Transition tool; not ideal for

permanent designs

! Specify network type (broadcast, point-to-point, etc.)

ip[v6] ospf network type

0x2009

Intra-area prefix LSA

N/A

debug ip[v6] ospf [ڲ]

! Toggle split-horizon and poison-reverse

[no] split-horizon

[no] poison-reverse

! Enable MD5 authentication (RIPv2 only)

ip rip authentication mode md5

ip rip authentication key-chain key-chain

Network Types

! Modify interface hello and dead intervals

ip[v6] ospf hello-interval seconds

ip[v6] ospf dead-interval seconds

Nonbroadcast

(NBMA)

Multipoint

Broadcast

Multipoint

Nonbroadcast

Broadcast

Point-to-Point

DR/BDR Elected

Yes

! Enable MD5 authentication (OSPFv2)

ip ospf authentication message-digest

ip ospf message-digest-key key-id md5 key-string

EIGRP

EIGRP Configuration

Neighbor Discovery

Hello/Dead Timers

30/120

Yes

30/120

Yes

10/40

Yes

10/40

! Enable EIGRP for an autonomous system

[ipv6] router eigrp AS-number

Metric Formula

! Enable IPsec authentication (OSPFv3)

ipv6 ospf auth ipsec spi spi-number { md5 | sha1 } string

Defined By

Supported Topology

RFC 2328

Full Mesh

RFC 2328

Any

Cisco

Any

Cisco

Full Mesh

Cisco

Point-to-Point

K 2 * bw

256 - load

K 5

rel + K 4

! Specify a router ID formatted in IPv4 dotted-decimal

[eigrp] router-id router-ID

256 * (K 1 * bw + + K 3 * delay ) *

Ğ bw = 10 7 / minimum path bandwidth in kbps

Ğ delay = interface delay in ´secs / 10

! Disable automatic classful summarization (IPv4 only)

no auto-summary

Integrated IS-IS

ISO Routing Levels

IS-IS Configuration

Level 0

Used to locate end systems

Packet Types

Default K Values

! Enable EIGRP on interfaces by network (IPv4 only)

network IPv4-address wildcard-mask

! Enable IS-IS routing

router isis

NSAP Addressing

Level 1

Level 2

Routing within an area (IS-IS)

Routing between areas (IS-IS)

1 Update

K 1 1

K 2 0

K 3 1

K 4 0

K 5 0

3 Query

4 Reply

Interdomain Part

Domain-Specific Part

! Modify maximum paths for equal-cost load balancing

maximum-paths 1-16

! Specify one or more NET addresses

net NET

Level 3 Inter-AS routing

NSAP

AFI

IDI

HODSP

System ID

SEL

5 Hello

8 Acknowledge

! Configure multiplier for unequal-cost load balancing

variance 1-128

! Set global routing level (default level-1-2)

is-type { level-1 | level-1-2 | level-2-only }

Terminology

Type-Length-Value (TLV)

Variable-length modular datasets carried by PDUs

Condensed

Area

Example

0005.80ff.f800.0000

0001

0000.0c00.1234

! Configure K values to manipulate the metric formula

metric weights 0 k1 k2 k3 k4 k5

! Configure IPv4 route summaries

summary-address IP-address subnet-mask [level]

Terminology

Interdomain Part (IDP)

Portion of the address used in routing between autonomous systems;

assigned by ISO

Domain-Specific Part (DSP)

Portion of the address relevant only within the local AS

Authority and Format Identifier (AFI)

Identifies the authority which dictates the format of the address

Initial Domain Identifier (IDI)

An organization belonging to the AFI

High Order DSP (HODSP)

The area within the AS

System ID

Unique router identifier; 48 bits for Cisco devices (often taken from an

Ethernet MAC address)

NSAP Selector (SEL)

Identifies a network layer service; always 0x00 in a NET

IS-IS Hello (IIH)

Establish and maintain neighbor adjacencies

Reported Distance

The metric for a route advertised by a neighbor

! Explicitly identify neighbors on NBMA links

neighbor IP-address interface

! Configure IPv6 route summaries

address-family ipv6

summary-prefix IPv6-prefix [level]

Link State PDU (LSP)

Carry TLVs encompassing link state information

Feasible Distance

The distance advertised by a neighbor plus the cost

to get to that neighbor

! Designate passive interfaces

passive-interface {interface | default}

Sequence Number Packet (SNP)

Used to request and advertise LSPs; can be complete

(CSNP) or partial (PSNP)

Network Entity Title (NET)

Unique router ID; includes area ID

Designated Intermediate System (DIS)

A pseudonode responsible for emulating point-to-

point links across a multi-access segment

! Originate a default route

default-information originate

Stuck In Active (SIA)

The condition when a route becomes unreachable

and not all queries for it are answered; adjacencies

with unresponsive neighbors are reset

Passive Interface

An interface which does not participate in EIGRP

but whose network is advertised

Stub Router

A router which advertises only a subset of routes,

and is omitted from the route query process

! Enable stub routing

[eigrp] stub [receive-only | connected | static | summary | redist]

interface type number

! Enable IS-IS on an interface

ip[v6] router isis

interface type number

! Enable EIGRP for IPv6 on the interface

ipv6 eigrp AS-number

! Specify interface routing level

isis circuit-type { level-1 | level-1-2 | level-2-only }

Adjacency Requirements

Ğ Interface MTUs must match

! Set the maximum bandwidth EIGRP can consume (can be >100%)

ip[v6] bandwidth-percent eigrp AS-number 1-999999

! Set interface metric

isis [ipv6] metric { 1-16777214 | maximum }

Ğ Levels must match

! Configure manual summarization of outbound routes

ip summary-address eigrp AS-number IPv4-address subnet-mask [AD]

ipv6 summary-address eigrp AS-number IPv6-prefix [AD]

Default Timers

Ğ Areas must match (if level 1)

! Designate the network as point-to-point

isis network point-to-point

Network Types

LAN (>T1)

WAN (<=T1)

Ğ System IDs must be unique

Ğ Authentication must succeed

Broadcast

Point-to-Point

Hello 5 sec

60 sec

DIS Elected Yes

! Configure DIS election priority

isis priority 0-127 [ level-1 | level-2 ]

! Enable MD5 authentication

ip[v6] authentication mode eigrp AS-number md5

ip[v6] authentication key-chain eigrp AS-number key-chain

Hold 15 sec

180 sec

Neighbor Discovery Yes

Hello/Dead Timers 10/30

Yes

10/30

DIS Election

Ğ Highest-priority interface elected

! Modify interface hello and dead intervals

isis hello-interval seconds [ level-1 | level-2 ]

isis hello-multiplier 3-1000 [ level-1 | level-2 ]

Troubleshooting

! Modify interface hello and hold timers

ip[v6] hello-interval eigrp AS-number seconds

ip[v6] hold-time eigrp AS-number seconds

Troubleshooting

Ğ Highest SNPA (e.g. MAC or DLCI) breaks tie

show ip[v6] eigrp {interfaces | neighbors }

show ip[v6] eigrp topology

Ğ Highest system ID breaks SNPA tie

show [clns | isis] neighbors

show isis [database | spf-log]

! Enable MD5 authentication

isis authentication mode md5

isis authentication key-chain key-chain

Ğ Default interface priority is 64

Ğ Current DIS may be preempted, unlike OSPF

clear ip[v6] eigrp [AS-number] neighbors

debug ip[v6] eigrp [neighbor]

! Toggle split horizon

[no] ip[v6] split-horizon eigrp AS-number

show clns interface

show isis [ipv6] topology

debug [clns | isis] [ڲ]

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