Cisco - Introduction to Routing Protocols 301

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Introduction to Routing Session 301

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Agenda

• Addressing • Concepts • Routing Protocols • Statics and Defaults

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ISO—OSI Reference Model Routing Information Protocol (RIP and RIPv2)

L7 L6 L5 L4 L3 L2 L1

Application Presentation Session Transport Network Layer Data Link Control Physical Layer

Interior Gateway Routing Protocol (IGRP) Open Shortest Path First (OSPF) Protocol NetWare Link Services Protocol (NLSP) Intermediate System to Intermediate System (IS-IS) Enhanced IGRP (EIGRP) Border Gateway Protocol (BGP)

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Router Functions • Routing = building maps and giving directions • Switching = moving packets between interfaces • Routers are packet switches • Path determination is overhead 301 0947_05F9_c2

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Introduction to IP Addresses UNIX Host

Internet TCP/IP

Company A

UNIX Host

Company B

• Unique addressing allows communication between end stations • Path choice is based on location • Location is represented by an address 301 0947_05F9_c2

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IP Addressing 32 Bits

Network 8 Bits

172 301 0947_05F9_c2

Host 8 Bits

.

16

8 Bits

8 Bits

. 122 . 204 7

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IP Address Classes

• Class A:

N

H

H

H

• Class B:

N

N

H

H

• Class C:

N

N

N

H

• Class D: for multicast N = Network number assigned by NIC H = Host number assigned by network administrator 301 0947_05F9_c2

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Host Addresses

172.16.200.11

E0

10.1.1.1

E1

172.16.3.10

10.250.8.11

172.16.12.12

10.180.30.118

IP: 172.16.2.1

172 .16

Routing Table Network Interface 172.16.0.0 E0

. 12 . 12

Network 301 0947_05F9_c2

IP: 10.6.24.2

Host

10.0.0.0

E1 9

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Subnet Addressing

172.16.2.11

E0

E1

172.16.2.2

172.16.3.100

172.16.2.160

172.16.3.150

IP: 172.16.2.1

172 .16 Network 301 0947_05F9_c2

172.16.3.5

2 .

Subnet

IP: 172.16.3.1

160 .

Host

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Routing Table Network Interface 172.16.2.0 E0 172.16.3.0

E1 10

5

Subnet Mask Network IP Address

172

Host

16

0

0

Network Default Subnet Mask

255

Host

255 Network

8-bit Subnet Mask

255

255

0

0

Subnet

Host

255

0

Use Host Bits, Starting at the High Order Bit Position 301 0947_05F9_c2

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Discontiguous IP Subnet A Where Is 172.16.0.0?

.5

192.168.1.4 255.255.255.252

B 172.16 172.16.40.1 255.255.255.0

172 172.16.50.1 255.255.255.0 .13

.6 192.168.1.12 255.255.255.252

.9 192.168.1.8 255.255.255.252

.14 .10

172.16 172.16.60.1 255.255.255.0

C

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Variable Length Subnet Mask A .5

172.16.1.4 255.255.255.252

B

172.16.50.1 255.255.255.0 .13

.6

172.16.40.1 255.255.255.0

172.16.1.12 255.255.255.252

.9 172.16.1.8 255.255.255.252

.14 .10

172.16.60.1 255.255.255.0

C

• Conserve IP addresses 301 0947_05F9_c2

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IPX Addressing 80 Bits

Network

Node

32 Bits

48 Bits

000C 15C0 301 0947_05F9_c2

0077.0650.2328

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Address Configuration Router (config-if) # ip address ip-address subnet-mask

• Assigns an address and subnet mask • Starts IP processing on an interface ipx network network

• Assigns a network number • Starts IPX processing on an interface • Must have ipx routing configured 301 0947_05F9_c2

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Classless Prefix Notation • 131.108.0.0/16 versus 255.255.0.0 • Summarizable blocks of subnets 131.108.48.0 /24

131.108.48.0 /21

131.108.49.0 /24 131.108.50.0 /24 131.108.51.0 /24 131.108.52.0 /24 131.108.53.0 /24 131.108.54.0 /24 131.108.55.0 /24 301 0947_05F9_c2

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IP Address Configuration Router (config) # ip netmask-format {bitcount | decimal | hexadecimal}

• Sets format of network mask as seen in show commands

• bitcount

172.16.31.6/24

• decimal

172.16.31.6 255.255.255.0

• hexadecimal

172.16.31.6 0xFFFFFF00

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Agenda

• Addressing • Concepts • Routing Protocols • Statics and Defaults

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Convergence • Time required for router to identify and use an alternate path • Dependent on timer values and algorithm • Difficult to predict precisely

x

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Load Balancing

T1

R2

T1

N1

N2 R4

R1 T1

R3

T1

• Equal cost paths • Rapid failover 301 0947_05F9_c2

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Load Balancing

R2

768K

N1

N2 R1

512K R3

R4 T1

• Unequal cost paths 301 0947_05F9_c2

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Holddown I Will Ignore Routes to X While in Holddown

x

• Sets minimum convergence time • Prevents routing loops 301 0947_05F9_c2

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Routing Loop: A Routing Disagreement

Packets for Network X

• Packets do not get to the destination • Temporary traffic surge until convergence 301 0947_05F9_c2

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Split Horizon

“ Do not send routing data back in the direction from which it came

” 301 0947_05F9_c2

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Split Horizon Frame Relay Network A PVC D

1

PVC

D

B S0

PVC C

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Turn off Split Horizon A 1,3

Frame Relay Network A

2

B

2

C

2

D

1

B

2

C

2

D

2

A PVC PVC

D

B

S0

PVC C

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Split Horizon Frame Relay Network

S0.1

B

2

C

2

D

1

A PVC PVC

D S0.3

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A

2

B

2

D

1

B

PVC C

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Metrics (Cost) • Numeric value used to choose among paths • RIP/RIPv2 is hop count and ticks (IPX) • OSPF/ISIS is interface cost (bandwidth) • (E)IGRP is compound • BGP can be complicated • Path determination depends on metric 301 0947_05F9_c2

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Agenda

• Addressing • Concepts • Routing Protocols • Statics and Defaults

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© 1999, Cisco Systems, Inc.

Routing Table One Forwarding Table Per Protocol (IP, IPX) Network #

Interface

Next Hop

Metric

Age

Source

198.113.181.0 Ethernet0 192.150.42.177 [170/304793] 02:03:50

D

198.113.178.0 Ethernet0 192.150.42.177 192.168.96.0

Ethernet0 192.150.42.177

192.168.97.0

Ethernet0

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[110/9936]

02:03:50

O

[120/3]

00:00:20

R

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Building the Routing Table

• Hardware state • Dynamic Routes are learned from a protocol

• Static Routes are manually defined 301 0947_05F9_c2

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Routing Protocols

A

I Know About: Network A Network B Network C

Routing Update

I Know About: Network X Network Y Network Z

B

X Y

Exchanges Network Knowledge

C

Z

• Routers are packet switches that forward traffic based on layer 3 logical addresses • Routing protocol updates are exchanged by routers to learn about paths to other logical networks • Each routing protocol offers features that can make it desirable as part of an internetwork design 301 0947_05F9_c2

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Routing Protocol Goals • Optimal path selection

• Easy to configure

• Loop-free routing

• Adapts to changes easily and quickly

• Fast convergence

• Does not create a lot of traffic

• Limited design administration

• Scales to a large size

• Minimize update traffic • Handle address limitations • Support hierarchical topology

• Supports variable length subnet masks and discontiguous subnets

• Incorporate rapid convergence 301 0947_05F9_c2

• Compatible with existing hosts and routers

• Supports policy routing 33

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IP RIP • Routing Information Protocol • Widely available • Hop count metric • Periodic update • Easy to implement • Usually free 301 0947_05F9_c2

• RFC 1058 • Simple = limited • Slow convergence • No VLSM • No discontiguous subnets • Routing loops • Count to infinity

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RIP—Distance Vector Net A

Net D

R1

R2 Net B S0 S0

E0

Network Interface A E0 B S0 C S0 D S0

R3 Net C S1

Network Interface B S0 C S1 A S0 D S1

S0

E0

Network Interface C S0 D E0 B S0 A S0

Send Routing Table to Neighbors 301 0947_05F9_c2

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Broadcast Routing Updates

RIP V1

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RIP Metric 1 Hop Path A

Hops

R2

T1

T1 56k

R1

R3

Path B 0 Hops 301 0947_05F9_c2

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When to Use RIP • Implementation in a few hours • Good for stable links • Good for small networks • routed in host environment • Multivendor environment • Non-redundant network 301 0947_05F9_c2

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RIP V2 • RFC 1723 • Cisco IOS® 11.1 support • Advertises masks • Variable length subnet masks • Route summarization • Routing updates use multicast • Authenticated updates using MD5 301 0947_05F9_c2

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Multicast Routing Updates

RIP V2

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When to Use RIPv2 • Same as RIP • Subnet mask support • Reduce broadcast load • Validated updates • Multivendor environment • Non-redundant network 301 0947_05F9_c2

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IPX RIP • Widely available • Hop count metric • Ticks (1/18 sec) • Periodic update • Easy to implement • Free on servers

• Tied to SAP protocol • Simple = limited • Slow convergence • No default route • Routing loops • Count to infinity

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IPX RIP—Ticks • Ticks are used to determine server timeout

• IPXWAN calculates for its interfaces

• Default for LAN interfaces is 1

• can be set via the ipx delay number interface sub command

• Default for WAN interfaces is 4 301 0947_05F9_c2

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IGRP • Interior Gateway • Routing Protocol • • Cisco developed • • Distance vector • • Compound metric 301 0947_05F9_c2

Cisco IOS 9.21 Periodic update No VLSM Default timers produce slow convergence

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IGRP Compound Metric • Administrative weight

T1 R2

• Delay • Bandwidth

T1

• Reliability

56k

• Load

R1

R3

(K2 * BW) K = ((K1 * BW + (256-load) + K3* delay)) * (reliability5 + K )) 4 301 0947_05F9_c2

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How the IGRP Metrics Work Delay MetricBased on D1 + D2 + D3

D1

D2

D3

Bandwidth Metric-Based on 64kbps

1.5 Mbps

64 kbps

1.5 Mbps

• Bandwidth dominates short paths • Delay dominates long paths • Configure bandwidth on all interfaces 301 0947_05F9_c2

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When to Use IGRP

• Simplicity of RIP • Good for small and medium networks • When metrics are important • Reduced routing overhead

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Enhanced IGRP • Extremely fast convergence • VLSM support • Discontiguous subnets • Arbitrary route summarization • Supports prefix and host routing 301 0947_05F9_c2

• Best of DV and LS • Low overhead • Guaranteed loop-free • Reliable, incremental update-based • Multiprotocol: IP, IPX®, AppleTalk • Easy to configure

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Advanced Distance Vector

A B C

1 13 20

Z

Q

Y

A B C

On Startup Routing Tables Are Exchanged; Routing Table Built Based on Best Paths from Topology Table

27 12 35

A B C

Q Z X

2 13 13

Y’s Table A B C

5 3 3

X

X’s Table

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A

B ..

27 1 5 12 ..

Z Q X Z ..

Topology Table

• Construct neighbor tables • Construct topology tables • Compute routes 49

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EIGRP Tables • Topology table

• Neighbor table

• Acted upon by DUAL • Keeps adjacent neighbor’s address • All routes advertised by neighbors • Keeps the hold time • List of neighbors for • Information for each route reliable transport • Routes passive or active 301 0947_05F9_c2

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Diffusing Update Algorithm (DUAL) • DUAL is a loop-free routing algorithm that performs a diffused computation of a routing table Uses a new routing algorithm Achieves fast convergence Network changes propagate only to affected nodes (“bounded updates”)

• No need for route holddown • Researched and developed by SRI International 301 0947_05F9_c2

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IPX EIGRP • Automatic redistribution of routes into RIP/SAP • Maximum network size is 224 hops vs 15 for RIP • Incremental SAPs sent, reducing bandwidth usage • All other benefits of EIGRP 301 0947_05F9_c2

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When to Use EIGRP

• Very large, complex networks • VLSM • For fast convergence • Little network design • Multiprotocol support 301 0947_05F9_c2

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Link State Routing Z’s Link State Q’s Link State Topology Information Is Kept in a Database Separate from the Routing Table

Z

Q

Y

A B C

Q Z X

2 13 13

• OSPF X’s Link State

X

• IS-IS • NLSP • DECnet V

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Link State Routing • Neighbor discovery • Constructing an LSA (Link State Advertisement) • Distribute LSA • Compute routes using SPF (Shortest Path First) • On network failure New LSAs flooded All routers recompute routing tables 301 0947_05F9_c2

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OSPF • Open Shortest Path First • Link state or SPF technology • Developed by OSPF working group of IETF (RFC 1253) • Designed expressly for TCP/IP Internet environment 301 0947_05F9_c2

• Fast convergence • Variable-length subnet masks • Discontiguous subnets • No periodic updates • Route authentication • Delivered two years after IGRP

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OSPF Areas and Rules Area Border Router

• Backbone area (0) must be present • All other areas must have connection to backbone

Area 2

Area 3 Area 0

Backbone Router

• Backbone must be contiguous

Area 4 Area 1

• Do not partition area (0) Internet 301 0947_05F9_c2

Internal Router

Autonomous System (AS) Border Router 57

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When to Use OSPF • Large hierarchical networks • Complex networks, except… Topology restrictive Additional network design

• VLSM • Fast convergence • Multivendor 301 0947_05F9_c2

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IS-IS • IS = Intermediate System

• ISO 10589 • Two types of areas:

• Dual IS-IS

Level-1 other areas

• Integrated IS-IS

Level-2 backbone

• Metric is 6 bits wide (1-63)*

• Default for each level

• All interfaces default to 10

• Much like OSPF

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NetWare Link Services Protocol • Derived from ISIS • NLSP specs 3 levels of routers • Only 2 levels are defined • Spec is Novell NLSP version 1.1 http://developer.novell.com /devres/langrp/specs/nlspspec.exe http://www.novell.com/documentation /en/kayak/nw411com/ipxrtenu/docmodul/ch3.html 301 0947_05F9_c2

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BGP • RFC 1771

• Many options for policy enforcement

• Border Gateway Protocol

• Classless Inter Domain Routing • Version 4 is current (CIDR) • Exterior routing • Widely used for protocol (vs. Internet backbone interior) • Autonomous • Uses TCP for systems transport 301 0947_05F9_c2

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BGP Basics Peering A

C

AS 100

AS 101 B

D

E

• Runs over TCP

AS 102

• Path vector protocol • Incremental update 301 0947_05F9_c2

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Internal BGP (IBGP) Peering AS 100 D A B

E

• • • • 301 0947_05F9_c2

BGP peer within the same AS Not required to be directly connected IBGP neighbors should be fully meshed Few BGP speakers in corporate network 63

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External BGP (EBGP) Peering A

AS 100

AS 101 C B

• Between BGP speakers in different AS • Should be directly connected • Don’t run an IGP between EBGP peers 301 0947_05F9_c2

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Policy Drives BGP Requirements Static Route

AS 200 BGP AS 100

BGP BGP

AS 400

AS 300

• Policy for AS 100: Always use AS 300 path to reach AS 400 301 0947_05F9_c2

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When Not to Use BGP Network Number

Static A

BB

C ISP Runs BGP

Advertise Default Network Via IGP Use a Static Route to Provide Connectivity

• Avoid BGP configuration by using default networks and static routes Appropriate when the local policy is the same as the ISP policy 301 0947_05F9_c2

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Agenda

• Addressing • Concepts • Routing Protocols • Statics and Defaults

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Static Routes

• Routes configured manually • Useful when few or just one route exist • Can be administrative burden • Frequently used for default route 301 0947_05F9_c2

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Floating Static Routes • A static route with a high distance • Can be overridden by dynamic info T1 172.16.3.2 3

ISDN

172.16.1.0 C15C0

172.16.3.1 3 ip route 172.16.1.0 255.255.255.0 172.16.3.1 140 ipx route C15C0 3.0000.0c15.3628 floating-static 301 0947_05F9_c2

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Default Routes • Route used if no match is found in routing table • Can be carried by routing protocols • Two models Special network number: 0.0.0.0 (IP) -2 (IPX) Flagged in routing protocol

• Protocols support multiple models 301 0947_05F9_c2

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Creating a Default Route

• RIP, RIPv2: network 0.0.0.0 • IGRP, EIGRP: ip default-network • OSPF: default originate • IPX: ipx route default • default gateway is for “host mode” 301 0947_05F9_c2

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Default IP Subnet 172.16.0.0

Internet s0

s1

172.16.1.0

• Two defaults For unknown networks For unknown subnets

• Controlled by ip classless 301 0947_05F9_c2

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Comparison of Routing Protocols

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Link State

Traditional Distance Vector

Advanced Distance Vector

Scalability

Good

Low

Excellent

Bandwidth

Low

High

Low

Memory

High

Low

Moderate

CPU

High

Low

Low

Convergence

Fast

Slow

Fast

Configuration

Moderate

Easy

Easy

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Internet Routing Protocols • IP routing protocols are characterized as Name

Type

Proprietary Function Updates Metric

VLSM

Summ

RIP

DV

No

Interior

30 Sec

Hops

No

Auto

RIPv2

DV

No

Interior

30 Sec

Hops

Yes

Auto

IGRP

DV

Yes

Interior

90 Sec

Comp

No

Auto

EIGRP

Adv DV

Yes

Interior

Trig

Comp

Yes

Both

OSPF

LS

No

Interior

Trig

Cost

Yes

Man

IS-IS

LS

No

Int/Ext

Trig

Cost

Yes

Auto

BGP

DV

No

Exterior

Trig

N/A

N/A

Man

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Topology/Technology Considerations • Routing and services overhead is usually not a big deal when you have a lot of bandwidth (i.e. LANs) • Protect WAN bandwidth using update-based protocols—more bandwidth and buffers for application traffic • High densities of sub(interfaces) can cause “hot spots” and router CPU overload • NBMA (Non-Broadcast Multi-Access) technologies always require good design practices 301 0947_05F9_c2

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For Further Reference… • Computer Networks, Third Edition by Andrew Tanenbaum (ISBN: 0-13349-945-6) • Interconnections : Bridges and Routers by Radia Perlman (ISBN: 0-20156-332-0) • Internetworking with TCP / IP, Volume 1: Principles, Protocols, and Architecture by Douglas Comer (ISBN: 0-13216-987-8) • IP Routing Fundamentals by Mark Sportack (ISBN: 1-57870-071-x) • IP Routing Primer by Robert Wright (ISBN: 1-57870-108-2) • OSPF Network Design Solutions by Thomas, Thomas M. (ISBN: 1-57870-046-9) 301 0947_05F9_c2

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Thank You! • Please fill out the survey • This was #301 Introduction to Routing • Related sessions: 304 Intro to IP Switching 307 Deploying IGRP/EIGRP 308 Deploying OSPF/NLSP/IS-IS 309 Deploying BGP 301 0947_05F9_c2

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© 1999, Cisco Systems, Inc.

Introduction to Routing Session 301

301 0947_05F9_c2

© 1999, Cisco Systems, Inc.

Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in USA. Presentation_ID.scr

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301 0947_05F9_c2

© 1999, Cisco Systems, Inc.

Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in USA. Presentation_ID.scr

79

40