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Alcatel-Lucent Routing Protocols

Module 1 — Introduction

Module 2 — Static Routing and Default Routes

Module 3 — Routing Information Protocol

Module 4 – Link-State Protocols

Module 5 — Open Shortest Path First

Module 6 — Intermediate System–to–Intermediate System

Module 7 — Border Gateway Protocol


Module 1 — Introduction

Module 0 | 3 All rights reserved © 2006-2007 Alcatel-LucentAlcatel-Lucent Interior Routing Protocols and High Availability

IP Addressing — Basic Subnetting

Subnetting allows a network to be subdivided into smaller networks with routing between them.

With basic subnetting, each segment uses the same subnet mask.

Potential for wasting IP addresses on links that do not require high client density

Easiest to implement

Required for classful routing protocols

VLSM allows the use of different subnet masks for different parts of the network.


IP Addressing — VLSM

Different subnet masks per network

Routing protocols must advertise the subnet mask with updates

More efficient use of IP addressing than basic subnetting

Requires a good understanding of subnetting

RFC 1878 defines VLSM

Routing protocols that support VLSM are:

RIPv2

OSPF

IS-IS

BGP


IP Addressing Review

IP addresses are broken into classes: A, B, C, and D

Class A: 255.0.0.0 or /8 Network Host Host Host

Network Network Host Host

Network Network Network Host

Multicast Multicast Multicast Multicast

Class B: 255.255.0.0 or /16

Class C: 255.255.255.0 or /24

Class D: 255.255.255.255 or /32


Section Objectives

Introduction to IP routing

Review of IP forwarding

Control plane vs. data plane functions

Common layer 3 routing protocols

— Distance vector

— Link state

Classful and classless addressing

Variable length subnet masking

Classless interdomain routing

Private IP addresses

Network address translation (NAT/PAT)


Movement of Data

1.1.1.2 2.2.2.2

1.1.1.1 2.2.2.1

3.3.3.1 3.3.3.2

Data

Source Dest. S D

1.1.1.2 2.2.2.2 A B

F

C

S

Data

Source Dest. WAN

1.1.1.2 2.2.2.2 PPP

F

C

S

Data

Source Dest. S D

1.1.1.2 2.2.2.2 C DF

C

S

(MAC address = A)

(MAC address = B)(MAC address = C)

(MAC address = D)


Packet Forwarding

When a router receives a packet, it:

Compares the destination IP address of the packet to the FIB

Looks for the longest (most specific) match

If no match is found, the packet is dropped.

If the packet is to be forwarded, the next hop and egress interface must be known.

If a match is found, the packet is sent to the next-hop address via the interface specified in the FIB.

The next-hop is the next router in the path toward the destination.

The egress interface is required for encapsulation.


Common IP Routing Protocols

Legacy routing protocols:

RIP version 1

RIP version 2

Modern routing protocols:

OSPF

IS-IS

BGP


Distance Vector Protocols

Distance = How far away

Vector = What direction (interface)

RIPv1, RIPv2, and BGP are distance vector protocols

Int 1/1/2

IP – 1.1.1.1

Int 1/1/2

IP – 2.2.2.1

IP – 3.3.3.1 IP – 3.3.3.2

Routing Table:

1.1.1.0 – Direct 1/1/2

3.3.3.0 – Direct 1/1/1

2.2.2.0 – 1 hop via 1/1/1

Routing Table:

2.2.2.0 – Direct 1/1/2

3.3.3.0 – Direct 1/1/1

1.1.1.0 – 1 hop via 1/1/1

Int 1/1/1 Int 1/1/1


Link-State Protocols

Link = An interface

State = Active or inactive interface

OSPF and IS-IS are link-state protocols

More complex than distance vector

Faster convergence

Triggered updates

Three databases:

Adjacency — Neighbor database

Topology — Link-state database

Routing — Forwarding database


Link-State Protocols (continued)

Adjacency database

2.2.2.0/24

– via 1/1/1 cost 20

– via 1/1/2 cost 40

Link-state database Forwarding database

Adjacency Database

RTR-B – on 1/1/1

RTR-C – on 1/1/2

Routing Table:

2.2.2.0/24 – via 1/1/1

LSDB

RTR - A

RTR - C

RTR - B

Network

2.2.2.0/24

1/1/1

1/1/2


Routing Table Management

Each routing protocol populates its routes into its RIB.

Each protocol independently selects its best routes based on the lowest metric.

The best routes from each protocol are sent to the RTM.

RTM

RIP

RIB

OSPF

RIB


Preference

The RTM may have a best route from multiple protocols.

Selection is based on lowest preference value.

The RTM sends its best route to the FIB.

This route is the active route and is used for forwarding.

OSPF

BGP

RTM FIB

RIP

RIB

OSPF

RIB

OSPF

BGP

RIB


Default Preference Table

Route type Preference Configurable

Direct attached 0 No

Static 5 Yes

OSPF internal 10 Yes

IS-IS Level 1 internal 15 Yes

IS-IS Level 2 internal 18 Yes

RIP 100 Yes

OSPF external 150 Yes

IS-IS Level 1 external 160 Yes

IS-IS Level 2 external 165 Yes

BGP 170 Yes


IP Addressing — Classful and Classless

10.1.1.0/24

Routing Table:

12.1.0.0 – direct 1/1/2

192.1.1.0 – direct 1/1/1

10.0.0.0 – 1 hop via 1/1/1

12.1.0.0/16

192.1.1.0/24 10.1.2.0/24

10.1.1.0 10.0.0.0

10.1.1.0/24

Routing Table:

12.1.0.0/16 – direct 1/1/2

192.1.1.0 /24 – direct 1/1/1

10.1.1.0/24 – 2 hops via 1/1/1

10.1.2.0/24 – 1 hop via 1/1/1

12.1.0.0/16

192.1.1.0/24 10.1.2.0/24

10.1.1.0/24

10.1.1.0/24

10.1.2.0/24

Classful

Classless


IP Addressing — VLSM

Different subnet masks per network

Routing protocols must advertise the subnet mask with updates.

High-order bits are not reusable.

Routing decisions are made based on the longest match.

A more efficient use of IP addressing than basic subnetting

Requires a good understanding of subnetting

RFC 1878 defines VLSM.

Routing protocols that support VLSM are:

RIPv2

OSPF

IS-IS

BGP


IP Addressing — VLSM Example

172.16.0.0 – 10101100.00010000.00000000.00000000 – Reserved for WAN segments

172.16.1.0 – 10101100.00010000.00000001.hhhhhhhh – First Ethernet segment

….

172.16.254.0 – 10101100.00010000.11111110.hhhhhhhh – Last Ethernet segment

255.255.255.0 – 11111111.11111111.11111111.00000000 – Ethernet mask

172.16.0.4 – 10101100.00010000.00000000.000001 hh – First WAN segment

172.16.0.252 – 10101100.00010000.00000000.111111 hh – Last WAN segment

255.255.255.252 – 11111111.11111111.11111111.111111 00 – WAN mask


Module 2 — Static Routing and Default Routes


• Routers need to know where networks are located and how best to access them.

• This can be accomplished statically with administrative commands.

What a Router Needs to Know

1.1.1.1 2.2.2.1

3.3.3.1 3.3.3.2

Routing Table:

1.1.1.0/24 – Direct

3.3.3.0/30 – Direct

2.2.2.0/24 – static via 3.3.3.2

Routing Table:

2.2.2.0/24 – Direct

3.3.3.0/30 – Direct

1.1.1.0/24 – static via 3.3.3.1

R1 R2

2.2.2.0/241.1.1.0/24

3.3.3.0/30


Static Routes — Basic Static Routes

• Configuration of static routes between stub networks and corporate locations

2.2.2.0/24

3.3.3.1 3.3.3.2

Corporate

Headquarters

static-route 2.2.2.0/24 next-hop 3.3.3.2

static-route 0.0.0.0/0 next-hop 3.3.3.1

R1 R2


Static Routes — Configuration Example

2.2.2.0/24

3.3.3.1 3.3.3.2

Corporate

Headquarters

config>router> static-route 0.0.0.0/0 next-hop 3.3.3.1


R1 R2


Default Routes — Basic Default Route

3.3.3.1 3.3.3.2

Corporate

Headquarters

2.2.2.0/24

R2# show router route-table

============================================================================

Route Table

============================================================================

Dest Address Next Hop Type Protocol Age Metric Pref

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

3.3.3.0/24 System Local Local 01d02h 0 0

2.2.2.0/24 System Local Local 08d03h 0 0

0.0.0.0/0 3.3.3.1 Remote Static 01d02h 1 5

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

R1 R2


Static Routes — Floating Static Routes

2.2.2.0/24

3.3.3.1 3.3.3.2

Primary pathCorporate

Headquarters

Backup

1.1.1.1

1.1.1.2


config>router> static-route 2.2.2.0/24 next-hop 1.1.1.2 preference 200

• Configuration of a floating static route between stub

networks and corporate locations

R1 R2


Static Route Verification — Show Command

The command below shows static routes configured in the routing table.

Context: show>router>

Syntax: static-route [[ip-prefix [/mask]] | [preference preference] | [next-hop ip-addr] | tag tag

Example: R1# show router route-table protocol static

==============================================================================

Route Table (Router: Base)

==============================================================================

Dest Address Next Hop Type Proto Age Metric Pref

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

2.2.2.0/24 3.3.3.2 Remote Static 00h01m34s 1 5


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

No. of Routes: 1

==============================================================================


Static Route Verification — Show Command (continued)

2.2.2.0/24

3.3.3.1 3.3.3.2

Corporate

Headquarters

R1# show router route-table 2.2.2.0/24

==============================================================================

Route Table (Router: Base)

===============================================================================

Dest Address Next Hop Type Proto Age Metric Pref

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


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

No. of Routes: 1

==============================================================================

R1 R2


Static Routes — Ping Command

2.2.2.2

2.2.2.0/24

3.3.3.1 3.3.3.2Corporate

Headquarters

R1# ping 2.2.2.2 detail

PING 2.2.2.2: 56 data bytes

64 bytes from 2.2.2.2 via fei0: icmp_seq=0 ttl=64 time=0.000 ms.





---- 2.2.2.2 PING Statistics ----

5 packets transmitted, 5 packets received, 0.00% packet loss

round-trip min/avg/max/stddev = 0.000/0.000/0.000/0.000 ms

R1#


Static Routes — Traceroute Command

2.2.2.0/24

3.3.3.1 3.3.3.2

Corporate

Headquarters

R1# traceroute 2.2.2.2

traceroute to 2.2.2.2, 30 hops max, 40 byte packets

1 3.3.3.2 <10 ms <10 ms <10 ms

2 2.2.2.2 <10 ms <10 ms <10 ms

2.2.2.2

R1 R2


Learning Assessment

1. Do static routes have a higher or lower preference value than dynamic routes?

2. What is the command syntax to create a static route in the 7750 SR?

3. A router has a default route, a static route to 10.10.8.0/24, and a route to 10.8.0.0/14 learned from RIP. Which route is used for a packet with destination address 10.10.10.10?


Module 3 — Routing Information Protocol


Section Objectives

Distance vector overview

Split horizon

Route poisoning

Poison reverse

Hold-down timers


Distance Vector Overview

100 Mb/s

1 Gb/s

1 Gb/s1 Gb/s

RTR-A RTR-B

RTR-C RTR-D

Routers send periodic updates to physically adjacent neighbors

Updates contain the distance (how far) and vectors (direction) for networks


Distance Vector Overview (continued)

The router processes and compares the information contained in the routing update received with what is in its routing table.

Update from neighbor

Process

and compare

with routing

table

Periodic update

Sent to neighbor

routers


Split Horizon

An adjacent router does not advertise networks back to the source of the network information.

RTR-A RTR-B RTR-CX

10.0.0.010.0.0.0 – 1 hop10.0.0.0 – 2 hops

Routing Table:

10.0.0.0 – 1 hop

via 1/1/1

Routing Table:

10.0.0.0 – 0 hops

via 1/1/1

Routing Table:

10.0.0.0 – 2 hops

via 1/1/1


Route Poisoning

When a network goes away, the sourcing router sets the hop value to infinity and sends a triggered update to its neighbors.

RTR-A RTR-B RTR-C

10.0.0.010.0.0.0 – 16 hops10.0.0.0 – 16 hops

Routing Table:

10.0.0.0 – 16 hops

via 1/1/1

Routing Table:

10.0.0.0 – 16 hops

via 1/1/1

Routing Table:

10.0.0.0 – 16 hops

via 1/1/1

X

Routing Table:

10.0.0.0 – 0 hops

via 1/1/1

Routing Table:

10.0.0.0 – 1 hop

via 1/1/1

Routing Table:

10.0.0.0 – 2 hops

via 1/1/1


Poison Reverse

Poison reverse is the only time that split horizon is violated. This helps to avoid loop creation when a network fails.

RTR-A RTR-B RTR-C

10.0.0.010.0.0.0 — 16 hops10.0.0.0 — 16 hops

X

10.0.0.0 — 16 hops

Poison reverse

10.0.0.0 — 16 hops

Poison reverse

Routing Table:

10.0.0.0 — 16 hops

via 1/1/1

Routing Table:

10.0.0.0 — 16 hops

via 1/1/1

Routing Table:

10.0.0.0 — 16 hops

via 1/1/1

Routing Table:

10.0.0.0 — 0 hops

via 1/1/1

Routing Table:

10.0.0.0 — 1 hop

via 1/1/1

Routing Table:

10.0.0.0 — 2 hops

via 1/1/1


Routing Table:

10.0.0.0 – 16 hop –

Via 1/1/1

Routing Table:

10.0.0.0 — 0 hops

via 1/1/1

Routing Table:

10.0.0.0 – 16 hop –

Via 1/1/0

Routing Table:

10.0.0.0 — 1 hop

via 1/1/1

Routing Table:

10.0.0.0 – 16 hop –

Via 1/1/1

Routing Table:

10.0.0.0 — 2 hops

via 1/1/1

Hold-Down Timers

Hold-down timers provide time for other routers to converge and reduce loops from being created when a network fails.

RTR-A RTR-B RTR-C

10.0.0.010.0.0.0 — 16 hops10.0.0.0 — 16 hops

X

Hold-down timer

180 seconds

Hold-down timer

180 seconds

Hold-down timer

180 seconds


Routing Table:

10.0.0.0 – 16 hop –

Via 1/1/0

Routing Table:

10.0.0.0 — 0 hops

via 1/1/1

Routing Table:

10.0.0.0 – 16 hop –

Via 1/1/1

Routing Table:

10.0.0.0 — 1 hop

via 1/1/1

Routing Table:

10.0.0.0 – 16 hop –

Via 1/1/0

Routing Table:

10.0.0.0 — 2 hops

via 1/1/1

Combined Loop Avoidance Techniques

Combined, all attributes function as follows:

RTR-A RTR-B RTR-C

10.0.0.010.0.0.0 — 16 hops10.0.0.0 — 16 hops

X

10.0.0.0 — 16 hops

Poison reverse

10.0.0.0 — 16 hops

Poison reverse

Hold-down timer

180 seconds

Hold-down timer

180 seconds

Hold-down timer

180 seconds


RIP Overview

Uses a hop-count metric

Sends updates of the routing table to neighbors

Maximum of 15 hops; 16 hops equals infinity

30-second advertisement interval by default

Authentication is available in RIPv2

VLSM is supported by RIPv2


RIP Overview (continued)

100 Mb/s

1 Gb/s

1 Gb/s 1 Gb/s

RTR-A RTR-B

RTR-C RTR-D


RIPv1 vs. RIPv2

RIPv1 RIPv2

Defined in RFC 1058 Defined in RFCs 1721, 1722, and 2453

Classful routing protocol Classless routing protocol

No subnet mask in updates Sends subnet mask in updates

Does not support VLSM Supports VLSM and CIDR

No manual route summarization Manual route summarization

Does not support authentication Supports authentication

Broadcast updates Multicast or broadcast updates


RIP – Major Component Configuration

Router

Interface (assumed to be already complete)

Route policies

RIP

Group

Neighbor


Module 4 – Link-State Protocols


Distance vector Link state

•Views the network topology from the neighbor’s perspective

•Adds distance vectorsfrom router to router

•Frequent, periodic updates:slow convergence

•Passes copies of the routingtable to neighbor routers

•Has a common view of theentire network topology

•Calculates the shortestpath to other routers

•Event-triggered updates:faster convergence

•Passes link-state routingupdates to other routers

Distance Vector vs. Link State


Link State Overview

Classless routing protocol

Sends subnet mask in update

Supports VLSM, CIDR, and manual route summarization

Supports authentication

Maintains multiple databases

Sends updates using multicast addressing

Link state-driven updates, periodic hellos


Link State Overview (continued)

Link = An interface

State = Active or inactive interface, cost

IS-IS and OSPF are link-state protocols

More complex than distance vector

Faster convergence

Triggered updates

Three databases:

Adjacency – neighbor database

Topology – link-state database

Routing – forwarding database



Adjacency database

2.2.2.0/24

via 1/1/2 cost 20

via 1/1/1 cost 40

Link-state database Forwarding database

Adjacency database

RTR-B – on 1/1/2

RTR-C – on 1/1/1

Routing table

2.2.2.0/24 via 1/1/2

LSDB

RTR - A

RTR - C

RTR - B

Network

2.2.2.0/24

1/1/2

1/1/1



Routing table

10.0.0.0/8 via 2.2.2.1

…

10.0.0.0/8

Via 2.2.2.1 Cost 10

Via 3.3.3.1 Cost 20

…

Step 1 – Updates received from peers

Step 2 – Topology databasecreated

Step 3 – SPF algorithm determines the best

path to destination networksStep 4 – Routing

table created

10.0.0.0/8

Via 2.2.2.1 Cost 10 – BEST

Via 3.3.3.1 Cost 20

…

10.0.0.0/8

3.3.3.0/30

.1

.2

2.2.2.0/30

.2

.1


Exchanging Link-State Information

A B C D

R1 Link-state packet

A 10

B 10

R1 R2 R3


B 10

C 10


C 10

D 10

Routers exchange LSPs with each other. Each begins with directly connected networks for which it has direct link-state information.


Building a Topological Database

A B C DR1 R2 R3


A 10

B 10


B 10

C 10


C 10

D 10


A 10

B 10


B 10

C 10


C 10

D 10


A 10

B 10


B 10

C 10


C 10

D 10


Calculating the SPF Tree and Populating the Routing Table

A B C DR1 R2 R3


A 10

B 10


B 10

C 10


C 10

D 10

SPF tree

SPF

R1Routing

table

1

2

3


SPF Algorithm

R1

10.0.0.0/8 (net1)

5

10

100

R3

R2

R1 LSDB

R1, R2, 5

R1, R3, 10

R2, R1, 5

R2, R3, 100

R3, R1, 10

R3, R2, 100

R3, net1, 0


SPF Algorithm (continued)

R1

10.0.0.0/8 (net1)

5

10

100

R3

R2

Step Candidate Cost to root SPF tree

1 — — R1, R1, 0

2 R1, R2, 5

R1, R3, 10

5

10

R1, R1, 0

3 R1, R3, 10 10 R1, R1, 0

R1, R2, 5

4 R1, R3, 10

R2, R3, 100

10

105

R1, R1, 0

R1, R2, 5

5 R3, net1, 0 10 R1, R1, 0

R1, R2, 5

R1, R3, 10

6 — — R1, R1, 0

R1, R2, 5

R1, R3, 10

R3, net1, 0


Link State – Topology Change

Run SPFUpdaterouting

table


table


table

Topologychange

Link-state updates are driven by topology changes.

Link-state information


Sequence Numbers

Sequence numbers must be included in the link-state information.

Without sequence numbers, the link-state information could be flooded indefinitely.

The sequence number remains the same, router-to-router, during the flooding process.

In a link-state environment, routers use the sequence numbers for the following decisions when they receive link-state updates:

If the sequence number is lower than the one in the database, the link-state information is discarded.

If the sequence number is the same as the one in the database, an ACK is sent. The link-state information is then discarded.

If the sequence number is higher, the link-state information is populated in the topological database, an ACK is sent, and the link-state information is forwarded to its neighbors.


Sequence Numbers (continued)

A B C D


Seq=2

R1 R2 R3


Seq=1


Seq=1

A B C D


Seq=2

R1 R2 R3


Seq=2


Seq=1


Sequence Numbers (continued)

B C

D

R2 R3

A

F E

R5 R4R6

R1

Z

R1 receives 2 copies of the link-state information for network Z.

— R1 must decide what to do with the second copy of the link-state information it receives.

Cost 20 Cost 20

Cost 10Cost 10

Cost 10 Cost 10


Link-State Information Aging

Link-state information includes an age field.

The age of newly created link-state information is set to 0 for OSPF and 1200 for IS-IS. It is incremented by every hop during the flooding procedure for OSPF and is decremented for IS-IS. The link-state age is also incremented for OSPF and decremented for IS-IS as it is held in the topological database.

Maximum age

When the link-state information reaches its maximum age, it is no longer used for routing. The link-state information is flooded to the neighbors with the maximum age, and the link-state information is removed from the topological database.


IS-IS – Packet Processing

A router deals with topology changes as follows:

LSU/LSA

Is entry in

LSDB?

Sequence No.

same?

Ignore

End

NoNo

No

Yes Yes

Yes

Add to LSDB

Send ACK

Flood LSA

Run SPF

Is sequence

number higher

than one in

LSDB?

Send LSU back

with newer

information


Hierarchy in Link-State Networks

Scalability issues exist for link-state networks:

The size of the link-state database increases exponentially with the size of the network.

The complexity of the SPF calculation also increases exponentially.

A topology change requires complete recalculation of the forwarding table on every router.

Hierarchy allows a large routing domain to be split into several smaller routing domains.

IS-IS and OSPF both implement hierarchy but use different techniques.

Hierarchy results in suboptimal routing.

Hierarchy is less common than in the past due to the increased capacity of routers.


IS-IS – Hierarchical View

Backbone (Level 2) links

Level 1 links

L1 Level 1

L2 Level 2

L1/L2 Level 1/Level 2

Area 1

Area 2

Area 3

L1L2

L1/L2

L1/L2

Integrated IS-IS Network

L1

L1/L2L1


OSPF – Hierarchical View (continued)

OSPF Hierarchical Routing

Area 0.0.0.0

Area 0.0.0.1 Area 0.0.0.2


Module 5 — Open Shortest Path First


OSPF v1

RFC 1131

defined

OSPF v2

Updated

RFC 1583

OSPF v2

Updated

RFC 2328

OSPF for

IPv6

RFC 2740

OSPF — RFC History

OSPF

workgroup

formed

OSPF v2

RFC 1247

defined

OSPF

work in

progress

OSPF v2

Updated

RFC 2178

1987

1998

1997

1994

1991

1989

Present

1999


OSPF — Protocol Overview


Subnet mask sent in update

Support for VLSM, CIDR, and manual route summarization

Support for authentication

Maintenance of multiple databases

Multicast addressing – 224.0.0.5 and 224.0.0.6

Link state-driven updates, periodic hellos


OSPF — Key Features

Key OSPF features are:

Backbone areas

Stub areas

NSSAs

Virtual links

Authentication

Support for VLSM and CIDR

Route redistribution

Routing interface parameters

OSPF-TE extensions


OSPF — Protocol Comparison

Feature

Updates

Update type

Transport

Authentication

Metric

Metric type

VLSM / CIDR support

Topology size

Convergence

RIPv2

Periodic

Broadcast/Multicast

UDP

Simple and MD5

Hops

Distance vector

Yes

Small/Medium

Slow

IS-IS

Incremental

L2 Multicast

Layer 2

Simple and MD5

Cost

Link-state

Yes

Large

Fast

OSPF

Incremental

L3 Multicast

IP

Simple and MD5

Cost

Link-state

Yes

Large

Fast


OSPF — Link-State Protocol Comparison

Feature

Updates

Multicast layer

Authentication

Metric

Metric type

LSA types

Area hierarchy

Area boundaries

Convergence

IS-IS

Incremental

Layer 2

Simple and MD5

Default: all ports cost 10

Link-state

L1 and L2

Not required

On segment

Fast

OSPF

Incremental

Layer 3

Simple and MD5

Auto-calculation on interface

Link-state

Multiple types

Backbone area

At interface

Fast


OSPF — Path Determination

OSPF uses SPF for path determination.

SPF uses cost values to determine the best path to a destination.

RTR-A

RTR-C

RTR-B

Cost 0 Cost 10

Cost 125 Cost 125

Cost 125

RTR-A

10.0.0.0 – Cost 260 via RTR C

*10.0.0.0 – Cost 135 via RTR B

* = Best path

10.0.0.0


Calculating Link Cost

Cost = reference-bandwidth ÷ bandwidth

The default reference-bandwidth is 100 000 000 kb/s or 100 Gb/s.

The default auto-cost metrics for various link speeds are as follows:

— 10-Mb/s link default cost of 10 000

— 100-Mb/s link default cost of 1000

— 1-Gb/s link default cost of 100

— 10-Gb/s link default cost of 10

The cost is configurable.


Configuration Basics

Interfaces must be configured in an OSPF area.

By default, interfaces in an area are advertised by OSPF.

Routes received through OSPF are advertised by OSPF.

No other routes are advertised by default.

Verify that adjacencies are formed with neighbors.

Verify that routes are in the routing table.


OSPF — Multicast Addressing

OSPF uses class D multicast addresses in the range 224.0.0.0 to 239.255.255.255.

Specially reserved addresses for OSPF:

224.0.0.5: All routers that speak OSPF on the segment

224.0.0.6: All DR/BDRs on the segment

IP multicast addresses use the lower 23 bits of the IP address as the low-order bits of the MAC multicast address 01-005E-XX-XX-XX.

224.0.0.5 = MAC 01-00-5E-00-00-05

224.0.0.6 = MAC 01-00-5E-00-00-06


OSPF — Generic Packet

OSPF packets use protocol number 89 in the IP header.

OSPF is its own transport layer.

Link header IP headerOSPF packet

typesLink trailer

IP header protocol

ID 89 = OSPF


OPSF — Packet Types

OSPF hello

OSPF database descriptor

OSPF link-state request

OSPF link-state update

OSPF link-state ACK


OSPF — Link Topology Types

Multi-access

Point-to-point


OSPF — Router ID

Each router must have a router ID, the ID by which the router is known to OSPF.

The default RID is the last 32 bits of the chassis MAC address.

Configuring a system interface overrides the default.

— Using a system interface is easier to document.


On point-to-point links, there is no need for a DR or BDR.

All packets are sent via IP multicast address 224.0.0.5.

Usually a leased-line (i.e., HDLC, PPP) segment

Can be configured on point-to-point Ethernets

RTR - A

RTR - C

RTR - B

Network

2.2.2.0/24

OSPF — Point-to-Point Segments


OSPF — LAN Communication

Election of the DR and BDR in multi-access networks:

C

1.1.1.1

D

1.1.1.2

E

1.1.1.3

A

1.1.1.5

B

1.1.1.4

Each router sends hellos.

The router with the highest priority is the DR.

If all priorities are the same, the DR is the router with the highest RID.

RTR-A

Has the highest

RID, so it will be

the DR

RTR-B

Has the second highest

RID, so it will be the BDR


OSPF — Exchanging Updates in a LAN

Election of the DR and BDR in multi-access networks:

RTR-C

1.1.1.1

D

1.1.1.2

E

1.1.1.3

RTR-A (DR)

1.1.1.5

RTR-B (BDR)

1.1.1.4

Routers use the 224.0.0.6 IP address to send updates to the DRs.

The BDR monitors the DR to ensure that it sends updates.

The DR uses 224.0.0.5 to send updates to all OSPF routers.

RTR-C sends update to

All DRs using IP address

224.0.0.6

RTR-A sends update to

All OSPF routers using

IP address 224.0.0.5


Module 6 — Intermediate System–to–Intermediate System


IS-IS — Protocol Overview

Development began prior to that of OSPF.

The U.S. government required ISPs to use IS-IS for early stages of the Internet.

IS-IS supports IPv6.

Many large enterprise networks and ISPs use IS-IS due to the scalability and stability of the protocol.


RFC 1629

NSAP and

Internet

RFC 33509

TLV

code points

IS-IS — RFC History

RFC 1142

Original

RFC1990

2002

…..

1994

1992

1990

RFC 1195

TCP/IP

support

ISO 10589

released

Present

IS-IS

work in

progress

Other IS-IS

RFCs

released


IS-IS — Protocol Overview (continued)


Subnet mask sent in update

Support for VLSM, CIDR, and manual route summarization

Support for authentication

Maintenance of multiple databases

Layer 2 multicast addressing

Link-state driven updates, periodic hellos


IS-IS — Key Features

Key IS-IS features are:

Area hierarchy

Authentication

Support for VLSM and CIDR

Route redistribution

Routing interface parameters

IS-IS TE extensions


IS-IS — Protocol Comparison

Feature

Updates

Update type

Authentication

Metric

Metric type

VLSM / CIDR support

Topology size

Summarization

Convergence

RIPv2

Periodic

Broadcast/Multicast

Simple and MD5

Hops

Distance vector

Yes

Small

Manual

Slow

OSPF

Incremental

L3 Multicast

Simple and MD5

Cost

Link-state

Yes

Very large

Manual

Fast

IS-IS

Incremental

L2 Multicast

Simple and MD5

Cost

Link-state

Yes

Very large

Manual

Fast


IS-IS — Link-State Protocol Comparison

Feature

Updates

Multicast layer

Authentication

Metric

Metric type

Update types

Area hierarchy

Area boundaries

Convergence

IS-IS

Incremental

Layer 2

Simple and MD5

Default: all ports cost 10

Link-state

L1 and L2

Not required

On segment

Fast

OSPF

Incremental

Layer 3

Simple and MD5

Auto-calculation on interface

Link-state

Multiple types

Backbone area

At interface

Fast


IS-IS — Frequently Used Terms

Area — Corresponds to the level 1 subdomain

End system — Typically a computer, printer, or other attached device

Intermediate system — Router in an IS-IS network

Neighbor — A physically adjacent router

Adjacency — A separate adjacency is created for each neighbor on a circuit and for each level of routing (level 1 and level 2) on a broadcast circuit.

Circuit — A single locally attached network

Link — The communication path between 2 neighbors

CSNP — Complete sequence number PDU

PSNP — Partial sequence number PDU

PDU — Protocol data unit


IS-IS — Frequently Used Terms (continued)

Designated IS — The intermediate system in a LAN that is designated to generate updates on behalf of the nodes in the LAN

Pseudo node — When a broadcast subnetwork has n connected intermediate systems, the broadcast subnetwork itself is considered to be a pseudo node.

Broadcast subnetwork — A multi-access subnetwork (such as Ethernet) that supports the capability of addressing a group of attached systems with a single PDU

General topology subnetwork — A topology that is modeled as a set of point-to-point links, each of which connects 2 systems

Routing subdomain — A set of intermediate systems and end systems that are located within the same routing domain

Level 2 subdomain — The set of all level 2 intermediate systems in a routing domain


IS-IS — Protocol Overview

IS-IS uses SPF for path determination.

SPF uses cost values to determine the best path to a destination.

RTR-A

RTR-C

RTR-B

Cost: 10 Cost: 10

Cost: 10 Cost: 10

Cost: 10

RTR-A

10.0.0.0: cost 30 via RTR-C

*10.0.0.0: cost 20 via RTR-B

* = Best path

10.0.0.0

Packet flow


IS-IS — ISO Network Addressing

IS-IS uses unique addressing (OSI NSAP addresses) compared to that of other IP routing protocols.

Each address identifies the area, system, and sector.

Routers with common area addresses form L1 adjacencies.

Routers with different area addresses form L2 adjacencies, if capable.

2-layer hierarchy:

Level 1: Builds the local area topology and forwards traffic to other areas through the nearest L1/L2 router

Level 2: Exchanges prefix information and forwards traffic between areas


IS-IS — ISO Network Addressing (continued)

Layer 2 multicast addressing is implemented to support IS-IS.

On Ethernet, the following multicast addresses are reserved:

L1 updates use 01-80-C2-00-00-14.

L2 updates use 01-80-C2-00-00-15.


IS-IS — Link-State Overview

Backbone (level 2) link

Level 1 link

L1 Level 1

L2 Level 2

L1/L2 Level 1/level 2

Area 49.0001

Area 49.0002

Area 49.0003

L1L2

L1/L2

L1/L2

L1

L1/L2L1


IS-IS — NSAP Addressing

IDP DSP

AFI System ID SELHigh Order-DSP

variable 6 1

Area ID System Address

NSAP — Network service access point

IDP — Initial domain part DSP — Domain specific part

AFI — Authority and format indicator IDI — Initial domain identifier(e.g., 49 is local assigned, binary)

High Order-DSP — High Order Domain Specific Part

SEL — N-selector (NSEL)

IDI

NSEL


IS-IS — Protocol Characteristics

Item Value

Maximum metric value assignable to a link 16 777 215

Maximum metric value for a path 4 261 412 864

All L1 IS multicast address 01-80-C2-00-00-14

All L2 IS multicast address 01-80-C2-00-00-15

SAP for IS-IS on 802.3 LANs FE

Protocol discriminator for IS-IS 83

NSAP selector for IS-IS 00

Sequence modulus 232

Size of LSP, which all IS routers must be able to handle 1492

Maximum age 1200

Zero life age 60

Maximum number of area addresses in a single area 3


IS-IS — Packet Format

IS-IS packets use layer 2 encapsulation of the media.

The Ethernet type field is set to 0xFEFE to denote an IS-IS packet instead of an IP packet.

The TLV identifies the type of information in the IS-IS packet.

IS-IS packets are called PDUs.

Ethernet header

Type = 0xFEFEIS-IS header IS-IS TLV Link trailer


IS-IS — Packet Format Details

Ethernet destination address:

01-80-C2-00-00-14 – L1 updates

01-80-C2-00-00-15 – L2 updates

Ethernet source address: source router interface MAC address

802.3 LLC DSAP and SSAP = FE:FE

Layer 3 protocol discriminator: 83

Ethernet header

Type = 0xFEFEIS-IS header IS-IS TLV Link trailer


IS-IS — Packet Format Details (continued)

IS-IS sends PDUs.

PDUs are encapsulated directly into the layer 2 frame.

There are 4 types of PDUs:

Hello (ESH, ISH, and IIH) — Maintain adjacencies

LSP (link-state packet) — Information about neighbors and links, generated by all L1 and L2 routers

PSNP (Partial Sequence Number PDU) — Specific requests and responses about links, generated by all L1 and L2 routers

CSNP — Complete list of LSPs exchanged to maintain database consistency


Module 7 — Border Gateway Protocol


BGP Scope

Enables the exchange of routing information between autonomous systems (AS)

An AS is a collection of routers that are under a single administration, which presents a consistent routing policy.

Enables the implementation of administrative policies

BGP has already scaled to:

Large number of ASs

Large number of neighbors

Large volume of table entries

High rate of change


Autonomous Systems in BGP

AS-65001

AS-65002

AS-65003

• An AS is a group of networks and network equipment under

a common administration.

• IGP protocols such as OSPF, IS-IS, and RIP run in an AS.

• BGP is used to connect ASs.


Autonomous Systems in BGP (continued)

Public autonomous systems:

Assigned by ARIN or another authority

Must be used when connecting to other ASs on the Internet.

Range from 0 to 64 511

Private autonomous systems:

Assigned by ISPs (for some clients) and local administrators

Not allowed to be advertised to other ISPs or on the Internet

Range from 64 512 to 65 535


BGP Features

Path vector protocol:

Neighbor is any reachable device

Unicast exchange of information

Reliability using TCP

Uses well-known TCP port 179

Periodic keepalive for session management

Event-driven

Robust metrics

Authentication

Similar behavior as other TCP/IP applications

Because BGP peers are not always directly connected, BGP relies on IGP to route between peers.


eBGP vs. iBGP Overview

2 types of BGP sessions are possible.

The routers may be in different ASs:

Called external BGP or eBGP

Typically directly connected, but not mandatory

Different administrations

The routers may be in the same AS:

Called internal BGP or iBGP

Typically remote, but could be directly connected

Same administration


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