Hp Switching and Routing Technologies

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HP Switching and Routing TechnologiesWeb-based Training Course Companion

Version 10.41


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Copyright 2010 Hewlett-Packard Development Company, L.P.The information contained herein is subject to change without notice. The only warranties for HP products and

services are set forth in the express warranty statements accompanying such products and services. Nothing

herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial

errors or omissions contained herein.

This is an HP copyrighted work that may not be reproduced without the written permission of HP. You may not use

these materials to deliver training to any person outside of your organization without the written permission of HP.

HP Switching and Routing Technologies

Web-based Training Course Companion

Rev. 10.41


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HP Switching and Routing Technologies Introduction

1 - 1Rev. 10.41

Module 1 Objectives

This module will introduce you to some of the challenges involved in providing high-qualityvoice and video on an existing data network. After completing this module, you will be able to:

Identify business and technological forces that have driven the development of convergednetworks

Describe how HP networking products can meet converged network demand for highavailability and predictability

Converged Applications Drive Infrastructure EnhancementsOrganizations typically implement converged solutions to lower the costs of services like voice telephonyand multimedia conferences, training, and presentations. At the same time, converged solutions enablegreater flexibility by integrating services formerly carried on separate networks.

IP Telephony Video conferencing anddistance learning

Video surveillance

While these integrated applications enhance user productivity, they place additional requirements on thein rastructure

Some applications may require the added flexibility provided by wireless access.

Video application support can mean high bandwidth at the edge, with even higher bandwidthrequirements at the distribution and core layers.

Network devices must support controls that enable prioritized handling for time-sensitive traffic.


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1 - 2Rev. 10.41

High availability is crucial in converged networks. Because all communication systems are concentrated in a singleinfrastructure, network outages would be particularly disruptive.

The Virtual Router Redundancy Protocol, which enables a standby router to automatically resume forwarding traffic ifthe rimar default atewa fails

HP networking products can enhance resilience on many levels by supporting:

Convergence Requires High Availability 1

The Spanning Tree Protocol, which blocks redundant switched links until a failure elsewhere may cause them totransition to the forwarding state

Multiple Spanning Tree, which defines separate active paths per instance, enabling utilization of redundant links anddevices that would otherwise remain inactive

Instance 1 Primary default gateway Instance 1 Backup default gateway

Instance 2 Backup default gateway Instance 2 Primary default gateway

Hosts in VLANsmapped to Instance 2




Links that are activefor Instance 1

Links that are activefor Instance 2

Redundant routed links between distribution and core layer switches maybe utilized if you select a routing protocol, such as OSPF, that supportsEqual-Cost Multipath (ECMP).

Connections to other resources and client systems

Convergence Requires High Availability 2

Distribution layer

ore ayerswitches

If both core switches in the example have access to the same resources, thedistribution layer switches can forward traffic over both equal-cost paths.

switches


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You can increase the availability of network devices by providing redundant hardware components within distribution

and/or core switches.

The HP E8200 switch series can be configured to provide resilience for hardware components.

Redundant management module failover to hot standby module

Redundant Components in Network Devices

Redundantmanagementmodules

Resilient switch fabric modules system can tolerate the loss of one module

Redundant, hot-swappable power supplies providing N+1 power protection are accessible from the rear of the unit

Resilient fabric

modules

Redundantpowersupplies

Real-time traffic, such as web video and VoIP, is far more sensitive to network congestion than typical IPdata traffic. To be successful, a converged network must exhibit predictable behavior under allcircumstances.

In this example, devices within the network cloud experience varying levels of congestion. Consequently,

Real-time Traffic Requires Predictability

- .

The outcome of the congestion is a variation in the interval between packet arrival, known as jitter,which results in a choppy voice or video stream.

Network users who experience high jitter levels are likely to be dissatisfied with the performance ofvoice and video applications, producing the perception that the network is not functioning properly.

Senders of real-time traffictransmit packets at fixedintervals.

Host 1

Receivers expect the packets toarrive at the same interval.

Host 2


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1 - 4Rev. 10.41

Traffic sent by this IP phone must reach the receiver in a timely manner. However, a certain amount ofdelay is inevitable as a message is sent through the network. One-way delay is defined as the intervalbetween the time the first bit in a packet is sent and the time it is received.

IP Telephony Traffic Requires Low Delay

Congestion can cause levels of delay that are unacceptable for IP telephony and video-conferencing. .

Phone 1 Phone 2

To minimize the effects of congestion on real-time traffic, a converged infrastructure requires intelligentdevices at the edge and core layers.

An HP networking edge switch and an IP phone negotiate parameters using a standardized mechanismknown as Link Layer Discovery Protocol for Media Endpoint Devices (LLDP-MED).

IP Telephony Requires Intelligence at the Edge

LLDP-MED

The phone identifies itself as a VOIPdevice, providing manufacturer and

The switch dynamically places the IPphone in appropriate VLAN and

other inventory information reports the VLAN ID to the phone.

Switch applies policies that will ensurevoice quality.

The phone adds appropriate802.1Q tag and priority settings tothe traffic it generates.

You will learn more about LLDP-MED and other topics relating to Quality of Service in Module 6.


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Module 1 Summary

In this module, you learned about traffic control and high availability features required tosuccessfully support a converged network.


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HP Switching and Routing Technologies Providing Redundant Links and Gateways

Rev. 10.41 2 - 1

Module 2: Providing Redundant Links and GatewaysObjectives

Each hosts default gateway is crucial in enabling its communication with remote resources.This module will describe the operation of Version 2 of the Virtual Router Redundancy Protocol(VRRP v2) and its interaction with the Spanning Tree Protocol.

After com letin this module ou will be able to:

Describe the interactions among network devices that support VRRP v2

Describe how multiple spanning tree instances enable two layer 3 switches to share defaultgateway responsibilities

Lesson 1 Introduction: 1

The source and destination IP addresses do notchange as packets make their way to the Server.Source and destination MAC addresses changewith every router hop. Dest. Source

Router_xDest.Source

Host1 PayloadServer Server

Router1

10.1.10.1/24

While the Layer 3 header on the packets from Host1to the Server contains the actual source anddestination IP addresses, the Layer 2 headerindicates that traffic is destined for the Host1sdefault gateway, Router1.

. . .

All destinationsoutside

10.1.10.0/24

ea er ea er

Host 110.1.10.100/24

Gateway: 10.1.10.1

All IP hosts require a gateway in theirlocal address range to reach non-localdestinations.

SwitchMAC headerDest. Source

Host1

IP headerDest.Source

Host1 PayloadRouter1 Server


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Rev. 10.41 2 - 2

If this router, or the path between the host and the router, becomes unavailable, thehosts open sessions terminate.

Even if an alternate path to remote destinations is available, the host may beunable to detect it. Regardless of the IP address assigned to the second routerinterface, its physical MAC address is different from that of the failed router

Lesson 1 Introduction: 2

Router1

. . .

All destinationsoutside

10.1.10.0/24

n erace.

The host will need to reconfigure its default gateway andestablish new sessions. The replacement router interfacecannot assume forwarding responsibility for open sessions.

The Virtual Router Redundancy Protocol (VRRP) maybe used to establish an active/standby model fordefault gateways, enabling the standby to resumeforwarding responsibilities for existing sessions and

Host 110.1.10.100/24

Gateway: 10.1.10.1

Switch

10.1.10.2/24

Router2

ose es a s e su sequen o a ure o e ac vegateway.

Version 2 of the Virtual Router Redundancy Protocol (VRRP) , which is specified in RFC 3768, providesan industry standard for automatic default gateway failover.

A VRRP virtual routeris a set of router interfaces on the same network with a common:

Virtual Router Identifier (VRID)

VRRP Terminology

Router1

Actual IP address:VLAN 10: 10.1.10.2/24


Non-owner (Backup)Owner (Master)

The Owneris the router interface whose actualIP address matches the virtualIP address.

Router1

Switch1

10.1.10.1 10.1.10.1VLAN 10 - Virtual Router ID: 1

Virtual IP address: 10.1.10.1

VLAN 10 Host: 10.1.10.10/24Default gateway: 10.1.10.1


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Rev. 10.41 2 - 3

In addition to a virtual IP address, a virtual MAC address isassigned to each virtual router.

VRRP Virtual MAC Address00:00:5e:00:01:01

First 40 bitsspecified inRFC 3768

The VRRP Master broadcasts a gratuitous ARP request that causeshosts on the VLAN to create an ARP cache entry associating thevirtual IP address with the virtual MAC address.

Router1



Non-owner (Backup)Owner (Master)

Router1

=Virtual Router ID

Switch1

10.1.10.1 10.1.10.1VLAN 10 - Virtual Router ID: 1

Virtual IP address: 10.1.10.1Virtual MAC: 00:00:5e:00:01:01


Gratuitous ARP Request

Ethernet header:Destination: Broadcast ff:ff:ff:ff:ff:ff)

- - - - -Type: ARP (0x0806)

Address Resolution Protocol header:Hardware type: EthernetProtocol type: IPSender MAC Address: IETF-VRRP-Virtual-Router-VRID-01 (00:00:5e:00:01:01)Sender IP Address: 10.1.10.1Target MAC Address: Broadcast (ff:ff:ff:ff:ff:ff)Target IP Address: 10.1.10.1

The defining characteristic of a Gratuitous ARP message is thecombination of broadcast as the Target MAC address, andmatchin valuesforSource and Tar et IP address The

Virtual Router ID

.message causes each host in this network to add the following

association to its ARP cache:

IP Address 10.1.10.1 = MAC Address 00:00:5e:00:01:01

Virtual IP Address


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Rev. 10.41 2 - 4

The VRRP Master indicates its availability by sending periodic advertisements to the VRRP multicastaddress, which is 224.0.0.18.

VRRP Advertisements

The VRRP Master broadcasts a gratuitous ARP request that causes hosts on the VLAN to create an ARPcache entry associating the virtual IP address with the virtual MAC address.

Router1

Backup VLAN 10: 10.1.10.2/24Master VLAN 10: 10.1.10.1/24

Router1

Switch1VLAN 10 Host: 10.1.10.10/24Default gateway: 10.1.10.1

VLAN 10 VRRPAdvertisement

VLAN 10 VRRP Advertisement

Ethernet header:Destination: 01:00:5e:00:00:12Source: 00:00:5e:00:01:01

IP datagram header:Protocol:VRRP (0x70)Source: 10.1.10.1 Destination: 224.0.0.18

Virtual Router Redundancy Protocol header:Version: 2Packet type:Advertisement (1)

Virtual Router ID: 1

Type: IP (0x0800)

This priority level indicates that the

This advertisement is sent to themulticast address assigned to VRRPin RFC 3768

r or y:

Count IP Addrs: 1Auth Type: No authentication (0)Advertisement Interval: 1 (sec)IP Address: 10.1.10.1

owner of the Virtual IP Address.

A copy if this advertisement is sentonce per second.


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Rev. 10.41 2 - 5

VRRP routers often support multiple VRIDs. In this implementation shown in the diagram, either routercan be Owner of any of the VRIDs.

While the VRRP Backup for a given VLAN does not act as gateway for its hosts, the router interface isfully functional. Traffic that enters a router through a VRRP Master interface can be forwarded onto adifferent VLAN through a Backup interface.

Load Sharing

Router1 Router2

VLAN 10 - VRID: 1: 10.1.10.1

VLAN 10: 10.1.10.2/24 (Backup)VLAN 20: 10.1.20.1/24 (Owner)

VLAN 10: 10.1.10.1/24 (Owner)VLAN 20: 10.1.20.2/24 (Backup)

Switch1

. . . . . . . . .Virtual MAC: 00:00:5e:00:01:01

10.1.20.1 10.1.20.1VLAN 20 : VRID2: 10.1.20.1

Virtual MAC: 00:00:5e:00:01:02



Router interfaces that are part of the same virtual router negotiate for the Master and Backup rolesbased on their priority settings. The Owner has the highest possible priority (255) and will alwaysassume the role of Master.

In the example below, Router1 is the Master for VLAN 10, and sends VRRP advertisements over thatVLAN. Router2 is the Master for VLAN 20.

VRRP Master Failover: 1

Router2

VLAN 10: 10.1.10.2/24 (Backup)VLAN 20: 10.1.20.1/24 (Master)

VLAN 10: 10.1.10.1/24 (Master)VLAN 20: 10.1.20.2/24 (Backup)

VRRP Backup routers listen for advertisements. If the Master stops sending advertisements, the Backupassumes the Master role.

Router1




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Rev. 10.41 2 - 6

VRRP Master Failover: 2

Router interfaces that are part of the same virtual router negotiate for the Master and Backup rolesbased on their priority settings. The Owner has the highest possible priority (255) and will alwaysassume the role of Master.

In the example below, Router1 is the Master for VLAN 10, and sends VRRP advertisements over thatVLAN. Router2 is the Master for VLAN 20.

Router2

VLAN 10: 10.1.10.2/24 (Master)VLAN 20: 10.1.20.1/24 (Master)

Router1

VRRP Backup routers listen for advertisements. If the Master stops sending advertisements, the Backupassumes the Master role.



Lesson 2 IntroductionTo enhance default gateway availability for client PCs, network designers often specify the use ofredundant uplinks from edge switches to routers.

Hosts in two VLANs are distributed over two edge switches. The edge switches have redundant uplinksto a pair of routing switches that will support VRRP.

All switch-to-switch links are members of both user VLANs.

VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24

VLAN 10: 10.1.10.2/24VLAN 20: 10.1.20.2/24

Router1 Router2

2010

Bridge Priority 0 (Root)

Tagged

Bridge Priority 4096 (Backup Root)

This lesson will describe some challenges and solutions that arise when VRRP and the Spanning TreeProtocol (STP) are combined within the same domain.

Switch1 Switch2

2010

2010

20

10

20

10Tagged Tagged

VLAN 10 Hosts:10.1.10.0/24

VLAN 20 Hosts:10.1.20.0/24

Tagged

Tagged

VLAN 10 Hosts:10.1.10.0/24

VLAN 20 Hosts:10.1.20.0/24


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Rev. 10.41 2 - 7

VRRP Advertisements and Spanning TreeThe routing switch configured as Spanning Tree Root should be configured as VRRP Owner. The Master

sends VRRP advertisements over each of link for each VLAN.When all links are up, the direct link between Master and Backup is the primary path for VRRPadvertisements. If the path between the VRRP Master and Backup is disrupted, the Backup will assertitself as the Master and this will prevent proper VRRP operation.

VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24

VLAN 10: 10.1.10.2/24VLAN 20: 10.1.20.2/24

Router2

Bridge Priority 0 (Root) Bridge Priority 4096 (Backup Root)

The edge switches, Switch1 and Switch2, cannot forward the VRRP advertisements toward the Backupbecause their uplinks to the Backup are in the Spanning Tree Blocking state.

For this reason, the direct Master-Backup link must carry all of the VLANs in this domain. Should this linkbecome unavailable, the remaining links must carry the advertisements for all VLANs.

Switch1 Switch2

BB

Gateway Load Sharing in a Single Spanning Tree: 1In a single Spanning Tree environment, a single active path carries traffic for all configured VLANs. Forthe efficiency of traffic flow, the Root of the tree should be the VRRP Master for all VLANs whose traffic iscarried by the links in the tree.

Because interfaces on Router1 serve as default gateway for both hosts, their traffic uses the same set oflinks in either direction.

VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24Bridge Priority 0 (Root)

VLAN 10: 10.1.10.2/24VLAN 20: 10.1.20.2/24Bridge Priority 4096 (Backup Root)

Router1 Router2

Dest. SourceHostA

Dest.SourceHostA PayloadRouter1 HostB

MAC headerDest. Source

Router1


HostA PayloadHostB HostB

Router1 delivers thepacket directly to Host B.

Switch1 Switch2

BB

Host B:10.1.20.10/24

Gateway: 10.1.20.1

Host A:10.1.10.10/24Gateway: 10.1.10.1

Because Router1 is HostAs gateway, its MACaddress appears in thepackets Layer 2 header.


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Rev. 10.41 2 - 8

Gateway Load Sharing in a Single Spanning Tree: 2In this load-sharing configuration, the VRRP Master for VLAN 20 does not correspond with the Spanning

Tree Root. Consequently, the uplink between Switch2 and its default gateway (Router2) is blocked bySpanning Tree. Traffic between Host B and its default gateway must first be forwarded at Layer 2through Router1 before reaching Router2.

Router1 forwards the packet at Layer 2 because the destination MAC address is not its own address.



Router1 Router2


Router2


HostB PayloadHostA HostA

Router1 forwards the packetto Router2 at Layer 2.

Router2 is the default gatewayfor Host B. However, theuplink from Switch 2 to Router2 is in Blocking state.


Router2


HostB PayloadHostA HostA

Switch1 Switch2BB

Host B:10.1.20.10/24

Gateway: 10.1.20.1

Host A:10.1.10.10/24Gateway: 10.1.10.1

Gateway Load Sharing in a Single Spanning Tree: 3The link between Router2 and Switch1 is blocked by Switch1. However, Router2s interface to thisnetwork is in the Forwarding state, and this enables Router2 to forward the packet directly to Host A.



Router1 Router2

Dest. SourceRouter2

Dest.SourceHostB PayloadHostA HostA

Router2 forwards the packetto Host A through Switch1.

Switch1 Switch2

BB

Host B:10.1.20.10/24

Gateway: 10.1.20.1

Host A:10.1.10.10/24Gateway: 10.1.10.1


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Rev. 10.41 2 - 9

VRRP and Multiple Spanning TreeThe Multiple Spanning Tree Protocol (MSTP) enables definition of multiple spanning tree instances.

Each Multiple Spanning Tree (MST) Instance can support a unique set of VLANs.

Spanning Tree parameters are separately configured for each instance, enabling definition of a RootBridge for each instance.

MSTP enables a set of routin switches to share atewa res onsibilities for a set of VLANs.

MST Instance 1: VLAN 10

Router1 Router2

MST Instance 2: VLAN 20Bridge Priority: 4096 (Backup Root)

MST Instance 1: VLAN 10Bridge Priority: 4096 (Backup Root)

MST Instance 2: VLAN 20

Bridge Priority: 0 (Root)

Bridge Priority: 0 (Root)

Switch1 Switch2BB

Host B:10.1.20.10/24

Gateway: 10.1.20.1

Host A:10.1.10.10/24Gateway: 10.1.10.1

Module 2 Summary

In this module, you learned the elements involved in the configuration of VRRP and MSTP.

Topics included:

The roles of Master and Backup routers in transmitting and receiving VRRP v2 advertisements

nteract ons among a vert sements an n s oc e y pann ng ree

How the configuration of Multiple Spanning Tree instances enables routers to share gatewayresponsibilities


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HP Switching and Routing Technologies IP Routing

3 - 1Rev. 10.41

Module 3: IP RoutingObjectives

A routing switch forwards traffic between its interfaces to enable communication among anycombination of local and remote networks.

After completing this module, you will be able to:

.

Describe how an IP router makes a forwarding decision when a packets destination matcheswith multiple route table entries.

List the differences between automatic and manual summarization of remote IP address space.

Describe how a router determines which route to place in its route table when the sameaddress range is advertised by different routing protocols or methods.

HostB:

While Layer 2 switches enable connectivity amongdevices within a network, the function of a router or Layer3 switch is to interconnect networks. It uses a packetsLayer 3 information to determine which of its interfacesleads to the destination, and creates a new Layer 2

Lesson 1 Introduction

RouterA

w c .

Routers may pass traffic between a pair of hosts locatedon directly connected networks.

The packets Layer 2 header contains the MAC addressof the interface that provides default gateway servicefor Network 1.

The router removes the existing Layer 2 header andcreates a new header with HostBs MAC address as

Network 3

Switch1

HostA:Network 1

HostC:Network 4

the destination.

A router may participate in forwarding traffic destinedfor remote hosts. The new Layer 2 header contains theMAC address of the next router on the path to thedestination host.


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Router interfaces are configured with an IP address and mask. When the router boots, it derives the rangeof addresses on its connected networks by applying the configured mask to each interface address.

The mask 255.255.255.0 indicates that the first 24 bits of the IP address represent the network portion.The last 8 bits represent the host portion of the address.

Local Networks and the IP Route Table

For each interface whose state is u , the router laces its network address ran e into the IP route table.

A router forwards traffic destined for local networks using the interface indicated in the IP route table.

The router drops traffic destined for address ranges not in the table.

RouterARouter interface 1:IP address: 10.1.10.1/24Subnet mask: 255.255.255.0

Router interface 2:IP address: 10.1.20.1/24Subnet mask: 255.255.255.0

Hosts in the range:10.1.20.0/24

Hosts in the range:10.1.20.0/24

Router Interface TypesRouters often support a variety of interface types in addition to the port-based interfaces shown on theprevious screen. These may include:

VLAN interfaces, which are considered up if at least one port member of the VLAN is active

Loopback interfaces, which are always considered up because they are not bound to any physicalinterfaces

VLAN 10 interface: 10.1.10.1/24

VLAN 20 interface: 10.1.20.1/24RouterA

Loopback 0: 10.1.0.25

Hosts in the range10.1.10.0/24

Hosts in the range10.1.20.0/24

Switch1


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Dynamic Routing Protocols

A router can learn about the existence of remote networks through dynamic interaction with neighboring

routers.

VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24 RouterARout in rotocols ma s eci f :

Routers that share information must follow a common protocol,which is set of rules for exchanging routing information.

. . .Loop 0: 10.1.0.25/32

Procedures for establishing neighbor relationships

The format of messages exchanged between neighbors

Conditions or events that require the routers to sendupdated information

10.1.10.0/2410.1.20.0/2410.1.0.25/32

VLAN 30: 10.1.30.1/24VLAN 40: 10.1.40.1/24VLAN 100: 10.1.100.2/24Loop 0: 10.1.0.26/32

RouterB

10.1.30.0/2410.1.40.0/2410.1.0.26/32

Static Route ConfigurationRouters can also learn about remote networks by static configuration. In this example, two VLANs aredirectly connected to each router.

The routers are connected by the network 10.1.100.0/24.

An administrator specifies the remote address range and the next hop toward the destination.

. . .VLAN 20: 10.1.20.1/24VLAN 100: 10.1.100.1/24Loop 0: 10.1.0.25/32

RouterA

VLAN 100:10.1.100.1/24

ip route 10.1.30.0/24 10.1.100.2 1

This command, issued at the CLI of RouterA, providesinformation the router will use to forward traffic toward thedestination network 10.1.30.0/24


RouterB

VLAN 100:10.1.100.2/24ip route 10.1.10.0/24 10.1.100.1 1

This command, issued at the CLI of RouterB, provides

information the router will use to forward traffic towardthe destinat ion network 10.1.10.0/24

Network topology, including Internet and intranet connectivity,determine appropriate methods for each situation.


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Dynamic interaction between routers falls into two basic categories.

1. Interior Gateway Protocols (IGP) facilitate theexchange of information among routers underthe same organizational control; that is, withinthe same Autonomous System (AS).

OSPF

AS 100ABC Corp - Europe

Routing Protocol Categories

BGP

2. Exterior Gateway Protocols (EGP) facilitate theexchange of route information among routersin different Autonomous Systems.

Routing Information Protocol (RIP)

Open Shortest Path First (OSPF)

Border Gateway Protocol version 4

Common examples of standard IGPs include:

AS 200ABC Corp

BGP/IS-IS

is t e current stan arfor Internet connectivity

Internet Service Providers often use an IGP,

such as IS-IS, within their own networks toenable connectivity among BGP routers. AS 300ABC Corp - Japan

RIP

Standard Interior Gateway Protocols: 1Standard Interior Gateway Protocols include:

1. Routing Information Protocol (RIP) is a distancevector protocol.

Each router sends periodic updates, based on

Network 1 cost 1Network 2 cost 1

Network 3

.

Information about remote networks is passedfrom router to router, with costs incrementingwith each hop.

Networ 1 cost 2Network 2 cost 2Network 3 cost 1

Network 4

Route tablees na on os ex op

Network 1 3 Router2Network 2 3 Router2Network 3 2 Router2Network 4 1 connected


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The Routing Information Protocol (RIP) uses a distance-vector algorithm to determine the best path to eachdestination.

Routers periodically advertise their route table entriesto RIP nei hbors, or eers.

RIP Advertisements: 1


RouterA

The advertisements contain a list of known addressranges (vectors), each of which is paired with the cost(distance) of the entire path to the address range.

10.1.100.1/24


RouterB

10.1.100.2/24


RouterA

RIP Advertisements: 2

Ethernet header:Dest: 01005e-000009 Source:

10.1.100.1/24a agram ea er:

Protocol: UDPSource: 10.1.100.1 Dest: 224.0.0.9

UDP header:Source: 520 (RIP) Dest: 520 (RIP)

Routing Information Protocol:Command: Response (2) Version: RIPv2 (2)Network: 10.1.0.25 Mask: 255.255.255.255 Metric: 1Network: 10.1.10.0 Mask: 255.255.255.0 Metric: 1

RIP v2 updates aresent to a reservedmulticast address

R

I

P

U

D

P

I

P

This router is configured to use splithorizon loop prevention. It does notinclude 10.1.100.0/24, which is theaddress range associated with thenetwork that carries this RIP update.


RouterB

10.1.100.2/24

Network: 10.1.20.0 Mask: 255.255.255.0 Metric: 1

Ethernet trailer:

M

AC


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RouterA

Updating the Route Table

When it receives RouterAs RIP advertisement, RouterBintegrates the address ranges into its route table, and

Before RouterB receives the RIP advertisement from RouterA,its route table contains only directly connected networks.

10.1.100.1/24ncremens e a ver se cos s.

Destination Gateway VLAN Type Metric

10.1.0.25/32 10.1.100.1 100 rip 2

10.1.0.26/32 lo0 connected 1

10.1.10.0/24 10.0.100.1 100 rip 2

10.1.20.0/24 10.0.100.1 100 rip 2

10.1.30.0/24 VLAN30 30 connected 1

10.1.40.0/24 VLAN40 40 connected 1

These networkswere advertisedwith a cost of 1.

IP Route Table: RouterB


RouterB

10.1.100.2/24

10.1.100.0 24 VLAN100 100 connected 1

RouterA

Generating RIP Advertisements:1The router generates a unique advertisement to send over each of its RIPinterfaces, based on the content of its route table.

The advertisement RouterB sends to RouterC includes its own connectednetworks and those it learned from RouterA.

10.1.100.1/24


10.1.0.25/32 10.1.100.1 100 rip 2

10.1.0.26/32 lo0 connected 1

10.1.10.0/24 10.0.100.1 100 rip 2

10.1.20.0/24 10.0.100.1 100 rip 2

10.1.30.0/24 VLAN30 30 connected 1

10.1.40.0/24 VLAN40 40 connected 1

10.1.100.0/24 VLAN100 100 connected 1


RouterB

10.1.100.2/24Connected networks:


.2.110.1.101.0/24

RouterC


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RouterA

Generating RIP Advertisements: 2

The router generates a unique advertisement to send over each of its RIPinterfaces, based on the content of its route table.

The advertisement RouterB sends to RouterC includes its own connectednetworks and those it learned from RouterA.

Ethernet header:

RIP advert isement : RouterB - VLAN 101 interface -10.1.101.2

10.1.100.1/24


10.1.0.25/32 10.1.100.1 100 rip 2

10.1.0.26/32 lo0 connected 1

10.1.10.0/24 10.0.100.1 100 rip 2

10.1.20.0/24 10.0.100.1 100 rip 2

10.1.30.0/24 VLAN30 30 connected 1

10.1.40.0/24 VLAN40 40 connected 1

10.1.100.0/24 VLAN100 100 connected 1


Dest: 01005e-000009 Source: IP datagram header:Protocol: UDPSource: 10.1.101.2 Dest: 224.0.0.9UDP header:Source: 520 (RIP) Dest: 520 (RIP)Routing Information Protocol:Command: Response (2) Version: RIPv2 (2)Network: 10.1.0.25 Mask: 255.255.255.255 Metric: 2Network: 10.1.0.26 Mask: 255.255.255.255 Metric: 1Network: 10.1.10.0 Mask: 255.255.255.0 Metric: 2

RouterB



.2.110.1.101.0/24

RouterC

Network: 10.1.20.0 Mask: 255.255.255.0 Metric: 2Network: 10.1.30.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.40.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.100.0 Mask: 255.255.255.0 Metric: 1

RouterA

Adding RIP Routes to the TableRouterC integrates the advertised address ranges into its route table,incrementing the costs.

IP Route Table: RouterC

10.1.100.1/24

10.1.0.25/32 10.1.101.2 100 rip 3

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.101.2 100 rip 3

10.1.20.0/24 10.0.101.2 100 rip 3

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2

10.1.101.0/24 VLAN101 101 connected 1

RouterB



.2.110.1.101.0/24

RouterC


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3 - 9Rev. 10.41

RouterA

Adding a Redundant Routed Link

Connected networks:VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24VLAN 100: 10.1.100.1/24

When another link is added, RouterC receives RIP updates fromRouterA that advertise a shorter path to some destinations.

The router increments the advertised cost of each network within theupdate, and compares this value with the cost associated with thenetwork in the route table.


10.1.0.25/32 10.1.101.2 100 rip 3

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.101.2 100 rip 3

10.1.20.0/24 10.0.101.2 100 rip 3

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2

IP Route Table: RouterC.2

10.1.102.0/24

10.1.100.0/24

: . . .Loop 0: 10.1.0.25/32.1

RouterBConnected networks:VLAN 50: 10.1.50.1/24VLAN 60: 10.1.60.1/24VLAN 101: 10.1.101.1/24VLAN 102: 10.1.102.1/24Loop 0: 10.1.0.27/32

.2.110.1.101.0/24

RouterC

10.1.101.0/24 VLAN101 101 connected 1

.1

Connected networks:VLAN 30: 10.1.30.1/24VLAN 40: 10.1.40.1/24VLAN 100: 10.1.100.2/24VLAN 101: 10.1.101.2/24Loop 0: 10.1.0.26/32

.2

RouterA

Replacing Route Table Entries: 1


The router replaces entries whose calculated cost is lower than thecost for that network in the route table.

When replacing route table entries, the router updates the value in theGateway field to match the Source address field in the IPdatagram header.


10.1.0.25/32 10.1.101.2 100 rip 3

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.101.2 100 rip 3

10.1.20.0/24 10.0.101.2 100 rip 3

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2


10.1.102.0/24

10.1.100.0/24

: . . .Loop 0: 10.1.0.25/32.1


.2.110.1.101.0/24

RouterC

10.1.101.0/24 VLAN101 101 connected 1

.1


.2


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3 - 10Rev. 10.41

RouterA

Replacing Route Table Entries: 2


The router replaces entries whose calculated cost is lower than the

cost for that network in the route table.

When replacing route table entries, the router updates the value in theGateway field to match the Source address field in the IPdatagram header.

IP datagram header:Protocol: UDPSource: 10.1.102.2 Dest: 224.0.0.9

RIP advertisement : RouterA int 10.1.102.2


10.1.0.25/32 10.1.102.2 102 rip 2

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.102.2 102 rip 2

10.1.20.0/24 10.0.102.2 100 rip 2

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2


10.1.100.0/24

: . . .Loop 0: 10.1.0.25/32.1

UDP header:Source: 520 (RIP) Dest: 520 (RIP)Routing Information Protocol:Network: 10.1.0.25 Mask: 255.255.255.255 Metric: 1Network: 10.1.0.26 Mask: 255.255.255.255 Metric: 2Network: 10.1.0.27 Mask: 255.255.255.255 Metric: 3Network: 10.1.10.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.20.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.30.0 Mask: 255.255.255.0 Metric: 2Network: 10.1.40.0 Mask: 255.255.255.0 Metric: 2Network: 10.1.50.0 Mask: 255.255.255.0 Metric: 3Network: 10.1.60.0 Mask: 255.255.255.0 Metric: 3Network: 10.1.100.0 Mask: 255.255.255.0 Metric: 1


.2.110.1.101.0/24

RouterC

10.1.101.0/24 VLAN101 101 connected 1

.1


.2

Network: 10.1.101.0 Mask: 255.255.255.0 Metric: 2

RouterA

Split Horizon Loop Protection: 1


Following Split Horizon rules, RouterCs subsequent RIPadvertisements to RouterA will omit the routes it has learnedthrough its connection to RouterA.


10.1.0.25/32 10.1.102.2 102 rip 2

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.102.2 102 rip 2

10.1.20.0/24 10.0.102.2 100 rip 2

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2


10.1.100.0/24

: . . .Loop 0: 10.1.0.25/32.1

10.1.102.0/24


.2.110.1.101.0/24

RouterC

10.1.101.0/24 VLAN101 101 connected 1

.1 Connected networks:VLAN 30: 10.1.30.1/24VLAN 40: 10.1.40.1/24VLAN 100: 10.1.100.2/24VLAN 101: 10.1.101.2/24Loop 0: 10.1.0.26/32

.2


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3 - 11Rev. 10.41

RouterA

Split Horizon Loop Protection: 2


Following Split Horizon rules, RouterCs subsequent RIP

advertisements to RouterA will omit the routes it has learnedthrough its connection to RouterA.

Split Horizon can decrease convergence time in a meshedtopology.


10.1.0.25/32 10.1.102.2 102 rip 2

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.102.2 102 rip 2

10.1.20.0/24 10.0.102.2 100 rip 2

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2


10.1.100.0/24

: . . .Loop 0: 10.1.0.25/32.1

10.1.102.0/24


.2.110.1.101.0/24

RouterC

10.1.101.0/24 VLAN101 101 connected 1


.2

Network: 10.1.0.26 Mask: 255.255.255.255 Metric: 2Network: 10.1.0.27 Mask: 255.255.255.255 Metric: 1Network: 10.1.30.0 Mask: 255.255.255.0 Metric: 2

Network: 10.1.40.0 Mask: 255.255.255.0 Metric: 2Network: 10.1.50.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.60.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.100.0 Mask: 255.255.255.0 Metric: 2Network: 10.1.101.0 Mask: 255.255.255.0 Metric: 1

RIP advertisement : RouterC int 10.1.102.1

RouterA

Poisoned Reverse Loop Protection: 1


Poisoned reverse is a variation on split horizon. Instead of omitting routes it learned from a neighbor,the RIP updates advertise these routes are advertised with a cost of 16, which means unavailable.

.2

10.1.100.0/24

: . . .Loop 0: 10.1.0.25/32.1

10.1.102.0/24


10.1.0.25/32 10.1.102.2 102 rip 2

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.102.2 102 rip 2

10.1.20.0/24 10.0.102.2 100 rip 2

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2



.2.110.1.101.0/24

RouterC .1 Connected networks:VLAN 30: 10.1.30.1/24VLAN 40: 10.1.40.1/24VLAN 100: 10.1.100.2/24VLAN 101: 10.1.101.2/24Loop 0: 10.1.0.26/32

.2

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2

10.1.101.0/24 VLAN101 101 connected 1


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3 - 12Rev. 10.41

RouterA

Poisoned Reverse Loop Protection: 2


Poisoned reverse is a variation on split horizon. Instead of omitting routes it learned from a neighbor,

the RIP updates advertise these routes are advertised with a cost of 16, which means unavailable.RouterC poisons the routes it has learned from RouterA only within theadvertisements it sends to RouterA. The updates RouterC sends toRouterB will advertise these routes with actual costs from its route table.


10.1.0.25/32 10.1.102.2 102 rip 2

10.1.0.26/32 l0.1.101.2 100 rip 2

10.1.0.27/32 lo0 connected 1

10.1.10.0/24 10.1.102.2 102 rip 2

10.1.20.0/24 10.0.102.2 100 rip 2

10.1.30.0/24 10.0.101.2 100 rip 2

10.1.40.0/24 10.0.101.2 100 rip 2


.2

10.1.100.0/24

: . . .Loop 0: 10.1.0.25/32.1

10.1.102.0/24Network: 10.1.0.26 Mask: 255.255.255.255 Metric: 16Network: 10.1.0.26 Mask: 255.255.255.255 Metric: 2Network: 10.1.0.27 Mask: 255.255.255.255 Metric: 1Network: 10.1.10.0 Mask: 255.255.255.0 Metric: 16Network: 10.1.20.0 Mask: 255.255.255.0 Metric: 16Network: 10.1.30.0 Mask: 255.255.255.0 Metric: 2


n cer a n mes e opoog es, po sone reverse can mproveconvergence speed when compared with split horizon.


.2.110.1.101.0/24

RouterC

10.1.50.0/24 VLAN50 50 connected 1

10.1.60.0/24 VLAN60 60 connected 1

10.1.100.0/24 10.0.101.2 100 rip 2

10.1.101.0/24 VLAN101 101 connected 1


.2

e wor : . . . as : . . . e r c:Network: 10.1.50.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.60.0 Mask: 255.255.255.0 Metric: 1Network: 10.1.100.0 Mask: 255.255.255.0 Metric: 2Network: 10.1.101.0 Mask: 255.255.255.0 Metric: 1

RIP Automatic Summarization: 1

Loop 0: 172.16.0.27/32VLAN 50: 172.16.50.1/24VLAN 102: 172.16.102.1/24

Routers A, B, and C are connected to another set of routerswhose network addresses are within a different classfulnetwork."Router D has interfaces in both classful networks, so its routetable shows individual subnets within each of the networks.

RouterARouterD

172.16.102.0/24

Loop 0: 172.16.0.26/32VLAN 30: 172.16.30.1/24VLAN 40: 172.16.40.1/24VLAN 101: 172.16.101.1/24VLAN 102: 172.16.102.2/24


.1

172.16.0.0/16 in the RIP updates it sends over VLAN100. It advertises individual networks within the10.0.0.0/8 range because the address associated withthe VLAN 100 is within that range.

RouterARouterD

172.16.101.0/24


10.0.100.0/24

RouterBRouterC

Network: 10.0.100.0 Mask: 255.255.255.0 Metric: 16Network: 10.1.0.25 Mask: 255.255.255.255 Metric: 16Network: 10.1.0.26 Mask: 255.255.255.255 Metric: 16Network: 10.1.0.27 Mask: 255.255.255.255 Metric: 16Network: 10.1.10.0 Mask: 255.255.255.0 Metric: 16Network: 10.1.20.0 Mask: 255.255.255.0 Metric: 16Network: 10.1.101.0 Mask: 255.255.255.0 Metric: 16Network: 172.16.0.0 Mask: 255.255.0.0 Metric: 1


29/102


3 - 13Rev. 10.41

Loop 0: 172.16.0.27/32VLAN 50: 172.16.50.1/24VLAN 102: 172.16.102.1/24

Routers A, B, and C are connected to another set of routers

whose network addresses are within a different classfulnetwork."Router D has interfaces in both classful networks, so its routetable shows individual subnets within each of the networks.

RouterARouterD

172.16.102.0/24


RIP Automatic Summarization: 2

.2

172.16.0.0/16 in the RIP updates it sends over VLAN100. It advertises individual networks within the10.0.0.0/8 range because the address associated withthe VLAN 100 is within that range.

RouterARouterD

172.16.101.0/24


10.0.100.0/24

RouterBRouterC

,a single advertisement to summarize the address spacewithin 10.0.0.0/8. It advertises individual networkswithin the 172.16.0.0/16 range because the address

associated with the VLAN 101 is within that range.

Network: 10.0.0.0 Mask: 255.0.0.0 Metric: 1Network: 172.16.0.25 Mask: 255.255.255.255 Metric: 1Network: 172.16.0.26 Mask: 255.255.255.255 Metric: 16

Network: 172.16.0.27 Mask: 255.255.255.255 Metric: 16Network: 172.16.10.0 Mask: 255.255.255.0 Metric: 1Network: 172.16.20.0 Mask: 255.255.255.0 Metric: 1Network: 172.16.30.0 Mask: 255.255.255.0 Metric: 16Network: 172.16.102.0 Mask: 255.255.255.0 Metric: 16

. . .

Dynamic routing protocols may need to be selectively enabled to control the flow of routing updates.Lesson 3 Introduction

Static routes may be selectively used in place of dynamic updates to minimize unnecessaryoverhead.

In this lesson, you will learn how to summarize contiguous address space using static routes.


30/102


3 - 14Rev. 10.41

This diagram illustrates a hierarchical topology that requires all traffic between locations to transit the core.Routers at locations A, B, and Cadvertise each of their networks toneighbor routers in the intranet core.

Dynamic Route Exchange

Intranet core range:10.0.0.0/16 Location C range:

10.3.0.0/16

RIP updates

each location the networks in all otherlocations.

Without further RIP configuration, eachrouter will need to support up to 1,024route table entries.

Location B range:10.2.0.0/16

Location A range:10.1.0.0/16

The Effect of Large IP Route Tables

Dynamic routing updates have the benefit of providing routers with the information they need to find thebest path to a given destination. However, the unrestricted flow of a large number of dynamic routingupdates can impact performance in two important ways:

0101 0 010 010 101 010

0110 1 110 000 111 0100101 0 010 010 101 010

.intervals can impact network performance.

2. A large number of route table entries can impact routerperformance.

Each RIP update interval (default: 30 seconds) mayrequire several update packets to contain all of thenetworks to be advertised.

Modern router architecture typically relies on packetcache and other techniques to minimize occasions when

0101 0 010 010 101 110

0001 1 010 010 101 010

0111 0 000 110 101 000

1101 0 010 000 101 010

0001 1 010 110 101 010

0111 0 010 011 101 010

0011 1 010 110 101 010

1101 0 010 000 101 010

packets must be submitted to the entire route table for

lookup. However, when the router performs a lookup onthe first packet in a flow, a smaller route table is moredesirable.


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3 - 15Rev. 10.41

Using a Default Static Route

There is another important reason to restrict dynamic routing updates between each location and theintranet core in this scenario:

Locations A, B, and C use a single point-to-point link to reach all remote

This router interfaceprovides the next hop forthe static default route.

Networks 10.3.0.0/24 10.3.0.255.0/24

Intranet core range:10.0.0.0/16

.unnecessary to maintain detailsregarding the networks at otherlocations.

All 4 billion addresses in the IP addressspace may be summarized as the defaultroute: 0.0.0.0/0.

Define staticdefault route here

10.2.0.0/16


Summarization by Location

The intranet core routers in this example can also use a static routes to summarize remote address space.

Routers in the intranet core will beconfigured with a static route for eachaddress range. Intranet core range:

RC

Location B range:Location A range:

. . .10.3.0.0/16

RB

RA

The next hop for each range will be aneighboring router interface at theremote location.

Network summarization requires that allnetworks within the summarized rangemust be reachable through the next hoprouter interface.

. . .. . .


32/102


3 - 16Rev. 10.41

Redundant Static Routes

Many routers and routing switches support configuration of multiple static routes that specify the samedestination.

If static routes are defined with differentcosts, the router will send all traffic to the

-

HP Networking E-series routing switches-

Intranet core range:10.0.0.0/16

RA2RA1RB2

Location C range:10.3.0.0/16

RC1

RC2

.Higher-cost routes will be used only afterfailure of lower cost routes.

A routers use of equal-cost static routeswill depend on whether it supports afeature typically referred to as ECMP,or Equal-Cost MultiPath.

-routes.

Location B range:10.2.0.0/16


Most Specific Route Table MatchRoute table entries specify a range of addresses that are defined using a starting address and mask.Some entries represent a single network, a VLAN or broadcast domain. Other entries may specify anaddress range that corresponds with a larger range of addresses.

When a packet is submitted for lookup, its destination address is compared with the contents of the routetable. It may match with multiple entries.

Destination Gateway VLAN Type Metric Distance

0.0.0.0 10.0.100.100 100 static 1 1

10.0.100.0/24 VLAN100 100 connected 1 0

10.1.0.0/16 10.0.102.1 102 static 1 1

10.1.1.0/24 VLAN1 1 connected 1 0

10.1.2.0/24 VLAN2 2 connected 1 0

10.1.10.0/24 10.1.64.2 64 rip 3 120

IP Route Table

When a packet matches with multipleroute table entries, it is forwarded usingthe gateway associated with the entrythat has the longest mask. This is alsoreferred to as the most specific match.

All destinations match with thedefault route (0.0.0.0/0).

Three entries in this route tablematch with the destination 10.1.1.15.

10.1.20.0/24 10.1.64.2 64 rip 3 120

10.1.30.0/24 VLAN30 30 connected 1 0

10.1.40.0/24 VLAN40 40 connected 1 0

10.1.64.0/24 VLAN64 64 connected 1 0

10.2.0.0/16 10.0.100.2 100 static 1 1

not match any entries.

This is the most specific match forthe destination 10.1.1.15.


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3 - 17Rev. 10.41

Administrative Distance

Each routing protocol applies its own interpretation to the metric value.Administrative distance provides a way for administrators to assign preference to one source of routinginformation over another.

Administrative distances may be modified from the system defaults.


0.0.0.0 10.0.100.100 100 static 1 1

10.0.100.0/24 VLAN100 100 connected 1 0

10.1.0.0/16 10.0.102.1 102 static 1 1

10.1.1.0/24 VLAN1 1 connected 1 0

10.1.2.0/24 VLAN2 2 connected 1 0

10.1.10.0/24 10.1.64.2 64 rip 3 120

10.1.20.0/24 10.1.64.2 64 rip 3 120

10.1.30.0/24 VLAN30 30 connected 1 0

IP Route TableDefault administrative distances forthis router:

Directly connected networks: 0

Static routes: 1

RIP-learned routes: 120

10.1.40.0/24 VLAN40 40 connected 1 0

10.1.64.0/24 VLAN64 64 connected 1 0

10.2.0.0/16 10.0.100.2 100 static 1 1

-

Static Route Redistribution into RIPIn the example, the static route is definedon Router A1, which is the router whoseneighbor leads to the remote addressrange 10.0.0.0/16.

Router A1 will advertise static routes


0.0.0.0 10.0.100.100 100 static 1 1

10.1.1.0/24 VLAN1 1 connected 1 0

10.1.10.0/24 10.1.64.2 64 rip 3 120

10.1.20.0/24 10.1.64.2 64 rip 3 120

10.1.30.0/24 VLAN30 30 connected 1 0

Router A1: IP Route Table

within its RIP update messages if RIPredistribution is enabled.

Static route was defined here:ip route 0.0.0.0/0 10.0.100.100

Address range:10.0.0.0/16

A3A1

Address range:10.1.0.0/16

. . . connec e

...

10.1.64.0/24 VLAN64 64 connected 1 0

A2

A4

A5Destination Gateway VLAN Type Metric Distance

0.0.0.0 10.1.64.1 64 rip 2 120

10.1.1.0/24 VLAN1 1 connected 1 0

10.1.10.0/24 VLAN10 64 rip 3 120

10.1.20.0/24 VLAN20 64 rip 3 120

10.1.30.0/24 10.1.64.1 64 rip 2 120

10.1.40.0/24 10.1.64.1 64 connected 1 0

...

10.1.64.0/24 VLAN64 64 connected 1 0

Router A2: IP Route Table


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3 - 18Rev. 10.41

Module 3 Summary

This module described basic IP routing concepts as they apply to forwarding among local andremote networks.

Topics included:

The categories of IP routing protocols

RIP advertisements

Using static routes to summarize address space


35/102

HP Switching and Routing Technologies Open Shortest Path First (OSPF)

4 - 1Rev. 10.41

Module 4: Open Shortest Path First (OSPF)Objectives

An intranet with redundant routed links will make the best use of the resilient design when it usesthe OSPF routing protocol, which can quickly respond to changes in link states.

After completing this module, you will be able to:

-, .

Describe how routing information propagates throughout an OSPF domain.

List OSPF router roles and the significance each has to sharing routing information.

Explain the functions of the OSPF message types.

Describe the OSPF area types and their proper uses.

Describe how remote address space is summarized within an OSPF domain.

Lesson 1 IntroductionOSPF has several advantages over RIP.

1. OSPF scales to larger intranets.

OSPF interfaces may be assigned metrics that aresensitive to the supported bandwidth.

ac rou er s a e o cons er n spee w enselecting the shortest path to a given destination. OSPFdoes not place a specific limit on network diameter.

Network B

Network CCost 100

2. OSPF router advertisements are more reliable.

An OSPF router advertisement describes the type,cost, and network address associated with itsconnected networks.

An OSPF router floods advertisements from itse wor

Cost 100Cost 10

R1

neighbors to all other neighbors intact, without

changing the contents of the advertisements.


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4 - 2Rev. 10.41

OSPF routers:

Are uniquely identified by a 32-bitdotted decimal value.

OSPF Router 10.0.0.32VLAN 100: 10.1.100.1Loop 0: 10.0.0.32

OSPF Hierarchy: Routers and Networks

Establish a formal relationship, knownas adjacency, with neighbors

10.0.0.32

10.1.0.32 10.2.0.32

10.0.100.0/24

All five routersare neighbors

on this network.

OSPF Router 10.1.0.32VLAN 100: 10.0.100.2

OSPF Router 10.2.0.32VLAN 100: 10.0.100.4

OSPF networks are identified by a startingaddress and mask.

10.1.0.33 10.2.0.33

Loop 0: 10.1.0.32/32

OSPF Router 10.1.0.33VLAN 100: 10.0.100.3Loop 0: 10.1.0.33/32

Loop 0: 10.2.0.32/32

OSPF Router 10.2.0.33VLAN 100: 10.0.100.5Loop 0: 10.2.0.33/32

Adjacency is a two-way relationshipbetween a pair of OSPF routers thatenables them to share routing information.

For the purposes of forming adjacency,

OSPF Network Types and Adjacency

number of neighbors it will support.

A point-to-point network cansupport at most two routerinterfaces. The routers will forman adjacency.

A multi-access network, such as Ethernet, cansupport more than two router interfaces. Thenumber of connections required to create a fullmesh of point-to-point adjacencies increases

significantly as neighbors are added.A full mesh wouldrequire 10 point-to-point adjacenciesN * (N 1)/2


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4 - 3Rev. 10.41

Designated Router and Backup Designated Router

OSPF routers with interfaces on multi-access networks may not always form a fulladjacency with all neighbors.

A Designated Router (DR) is elected for eachmulti-access network. The DR forms anadjacency with all neighbors on the network.

An elected Backup Designated Router (BDR)also becomes adjacent with all neighbors onthe network.

Non-DRs are adjacent to the DR and BDR,but do not become adjacent to each other.

DR BDR

OSPF Hierarchy: Areas

Area 2.0.0.0

Area 0.0.0.0

Area 1.0.0.0

The next level of OSPF hierarchy isthe area. Areas are identified by adotted decimal number.

OSPF area boundaries define the

OSPF Autonomous System (AS)

Each network can belong to onlyone area. The router interfacesconnected to a given network canform adjacencies only if they agree

scope of certain types of link stateadvertisements. IP address spacemay be summarized at areaboundaries.

.

The highest level in the hierarchy isthe Autonomous System (AS), whichis a collection of OSPF areas undercommon administration.


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4 - 4Rev. 10.41

Area Border Routers (ABR): 1

Area 2.0.0.0

Area 0.0.0.0

Area 1.0.0.0

OSPF areas are interconnected byarea border routers (ABR). Areaborder routers are configured withat least one interface in theAutonomous S stem backbone

OSPF Autonomous System (AS)

area, which interconnects all otherareas and uses the reserved ID0.0.0.0.

Area Border Routers (ABR): 2

OSPF Router 10.1.0.32Area 0.0.0.0 Networks:VLAN 100: 10.0.100.2/24 10.0.100.0/24

OSPF Router 10.1.0.33Area 0.0.0.0 Networks:VLAN 100: 10.0.100.3/2410.0.100.0/24

ABRs maintain adjacencieswith neighbors in two

different areas.

10.1.64.0/24

10.1.65.0/24 10.1.66.0/24

Area 1.0.0.0 Networks:Loop 0: 10.1.0.32/32

VLAN 64: 10.1.64.1/24VLAN 65: 10.1.65.1/24VLAN 67: 10.1.67.1/24

10.1.68.0/24

10.1.67.0/24

Area 1.0.0.0 Networks:Loop 0: 10.1.0.33/32

VLAN 64: 10.1.64.2/24VLAN 66: 10.1.66.1/24VLAN 68: 10.1.68.1/24

OSPF Router 10.1.0.34Area 1.0.0.0 Networks:Loop 0: 10.1.0.34/32

OSPF Router 10.1.0.35Area 1.0.0.0 Networks:Loo 0: 10.1.0.35/32

10.1.10.0/24

10.1.20.0/24

10.1.30.0/24

10.1.40.0/24

VLAN 65: 10.1.65.2/24

VLAN 68: 10.1.68.2/24VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24

VLAN 66: 10.1.66.2/24

VLAN 67: 10.1.67.2/24VLAN 30: 10.1.30.1/24VLAN 40: 10.1.40.1/24All interfaces of

each non-ABR arelocated within the

same area.


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4 - 5Rev. 10.41

OSPF Router Startup

ID: 10.1.0.25

OSPF Area 1.0.0.0 Networks:VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24VLAN 64: 10.1.64.1/24Loop 0: 10.1.0.25/32

RouterA

This advertisement, which is indexed by the unique RouterID, is stored in a database and transmitted to the routers

When OSPF is activated on a router, it generates a link stateadvertisement (Router LSA) that describes the characteristicsof its connected networks.

neighbors after they have begun to form an adjacency.

Most routers enable static configuration of a Router ID. In theabsence of static configuration, many routers will choose anaddress associated with the routers loopback interface.

Router ID: 10.1.0.25 Area 1.0.0.0 Link State Database

Link State Advertisement Type: Router LSA (1)Link State ID: 10.1.0.25

Advertising Router: 10.1.0.25

ID: 10.1.0.26

RouterB

Number of Links: 4Type: Stub ID: 10.1.0.25 Data: 255.255.255.255 Metric: 1Type: Stub ID: 10.1.10.0 Data: 255.255.255.0 Metric: 1Type: Stub ID: 10.1.20.0 Data: 255.255.255.0 Metric: 1

Type: Stub ID: 10.1.64.0 Data: 255.255.255.0 Metric: 1

The networks are considered Stub type because the router has noadjacent neighbors on these networks.

Exchanging Hello Messages: 1

ID: 10.1.0.25


RouterA

Link state advertisements can flow only over adjacencies. Thismakes adjacency establishment an important initial goal foreach OSPF interface.

The Hello message is the first step in establishingadjacency. In the example, RouterA has four connectednetworks. The router will send Hello messa es over all

O

S

P

F

I

P

M

A

C

active interfaces.


IP datagram header:Protocol: 89 (OSPF)Source: 10.1.64.1 Dest: 224.0.0.5

OSPF Header:OSPF Version: 2 Messa e T e: He llo acket 1

OSPF Hellomessages are sentto a reservedmulticast address

ID: 10.1.0.26

RouterB

Source OSPF Router: 10.1.0.25

Area: 1.0.0.0OSPF Hello Packet Header:Network Mask: 255.255.255.0Hello interval: 10 secondsRouter Priority: 1Router Dead Interval: 40 secondsDesignated Router: 10.1.64.1Backup Designated Router: 0.0.0.0

This router has noneighbors on thisnetwork. It assumes therole of Designated Router.


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4 - 6Rev. 10.41

Exchanging Hello Messages: 2

ID: 10.1.0.25


RouterA

Link state advertisements can flow only over adjacencies. This

makes adjacency establishment an important initial goal foreach OSPF interface.

The Hello message is the first step in establishingadjacency. In the example, RouterA has four connectednetworks. The router will send Hello messa es over all

O

S

P

F

I

P

M

A

C

active interfaces.

RouterA continues sending periodic Hello packets indefinitely,regardless of whether any neighboring routers reply withHello packets.

When OSPF is enabled on RouterB, it begins sending Hellomessages as well.

ID: 10.1.0.26

RouterB

Synchronizing Link State Databases

ID: 10.1.0.25


RouterA

Link state advertisements can flow only over adjacencies. Thismakes adjacency establishment an important initial goal foreach OSPF interface.

The Hello message is the first step in establishingadjacency. In the example, RouterA has four connected

O

S

P

F

I

P

M

A

C

newor s. e rouer w sen e o messages over aactive interfaces.

RouterA continues sending periodic Hello packets indefinitely,regardless of whether any neighboring routers reply withHello packets.

When OSPF is enabled on RouterB, it begins sending Hellomessages as well.

ID: 10.1.0.26

RouterB


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4 - 7Rev. 10.41

ID: 10.1.0.25

RouterAOSPF Area 1.0.0.0 Networks:VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24VLAN 64: 10.1.64.1/24Loop 0: 10.1.0.25/32

Synchronizing Link State Databases: 1

A goal of adjacency is the initial synchronization of thecontents of the two neighbors link state databases.In the next phase of adjacency formation, each routerdescribes the contents of its link state database bysending the headers of its stored link state advertisements

DatabaseDescription

Packet

.

RouterA sends its LSA headers, and RouterBcompares the neighbors headers with those in itsown database.

ID: 10.1.0.26

RouterB

OSPF Area 1.0.0.0 Networks:


ID: 10.1.0.25




.

RouterA sends its LSA headers, and RouterB compares theneighbors headers with those in its own database.

DatabaseDescription

Packet

Ethernet header:Dest: Source:


OSPF Header:

Database Description packetsare sent to the neighbors

unicast IP address.

ID: 10.1.0.26

RouterB


OSPF Version: 2

Message Type: DB Descr. (2)Source OSPF Router: 10.1.0.25Area: 1.0.0.0Database Description Header:LSA Type: Router LSA (1)Link State ID: 10.1.0.25

Advertising Router: 10.1.0.25LS Sequence Number: 80000000

These items identify thismessage as the first instanceof the Router LSA advertised

by Router ID 10.1.0.25.


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4 - 8Rev. 10.41

ID: 10.1.0.25




.


Link-state

RouterB sends a Link State Request packet, requesting LSAs thatare not in its own database, and RouterA sends a Link StateUpdate packet containing its own self-originated Router LSA.

Link-stateUpdatePacket

ID: 10.1.0.26

RouterB



equesPacket

Synchronizing Link State Databases: 5Link State Request Packet


Protocol: 89 (OSPF)Source: 10.1.64.2 Dest: 10.1.64.1

OSPF Header:OSPF Version: 2Message Type: LS Request (3)Source OSPF Router: 10.1.0.26

Area: 1.0.0.0Link State Request Header:LSA Type: Router LSA (1) RouterB includes header

information for the LSAs . . .Advertising Router: 10.1.0.25LS Sequence Number: 80000000

required to synchronize its

database with RouterA.


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4 - 9Rev. 10.41

Synchronizing Link State Databases: 6Link State Update Packet


IP datagram header:Protocol: 89 (OSPF)ource: . . . es : . . .

OSPF Header:OSPF Version: 2Message Type: LS Update (4)Source OSPF Router: 10.1.0.25

Area: 1.0.0.0LS Update Packet:Number of LSAs: 1LS Type: Router-LSALink State ID: 10.1.0.25

While the Database Description and LinkState Request packets include only LSAheaders, the Link State Update packetprovides detail about the advertising

routers connected networks.

ver s ng ouer: . . .LS Sequence Number: 80000000Number of Links: 4

Type: Stub ID: 10.1.0.25 Data: 255.255.255.255 Metric: 1Type: Stub ID: 10.1.10.0 Data: 255.255.255.0 Metric: 1

Type: Stub ID: 10.1.20.0 Data: 255.255.255.0 Metric: 1Type: Stub ID: 10.1.64.0 Data: 255.255.255.0 Metric: 1

ID: 10.1.0.25


A goal of adjacency is the initial synchronization of thecontents of the two neighbors link state databases.In the next phase of adjacency formation, each routerdescribes the contents of its link state database bysending the headers of its stored link state advertisementsLSA within Database Descri tion ackets


.


Link-state

RouterB sends a Link State Request packet, requesting LSAs thatare not in its own database, and RouterA sends a Link StateUpdate packet containing its own self-originated Router LSA.

Database synchronization occurs concurrently in bothdirections during adjacency formation. RouterB describes its

ID: 10.1.0.26

RouterB


c now e gmenPacket

. ,RouterB provides them.

After both routers have explicitly acknowledged receipt ofthe Link State Update packets, adjacency is complete.


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4 - 10Rev. 10.41

Synchronizing Link State Databases: 8Link State Acknowledgment Packet


IP datagram header:Protocol: 89 (OSPF)ource: . . . est: . . .

OSPF Header:OSPF Version: 2Message Type: LS Acknowledge (5)Source OSPF Router: 10.1.0.26

Area: 1.0.0.0Link State Request Header:LSA Type: Router LSA (1)Link State ID: 10.1.0.25

Advertising Router: 10.1.0.25

Like the Link State Request, theacknowledgment contains LSA header

information. If RouterA does notreceive an acknowledgment, it willretransmit the Link State Update.

equence um er:

ID: 10.1.0.25

In this example, only two routers are connected over anEthernet network. However, Ethernet is considered a multi-access network type, and this requires the election of aDesignated Router and Backup Designated Router.

RouterAOSPF Area 1.0.0.0 Networks:

VLAN 10: 10.1.10.1/24VLAN 20: 10.1.20.1/24VLAN 64: 10.1.64.1/24

You can issue CLI commands that will display the routers roleon a multi-access network. This information is also included in

The Network LSA: 1

oop : . . .

Hello

Hello messages sent by any neighbor on the network.



OSPF Header:OSPF Version: 2 Message Type: Hello packet (1)

ID: 10.1.0.26

RouterB


Hello

Source OSPF Router: 10.1.0.25

Area: 1.0.0.0OSPF Hello Packet Header:Network Mask: 255.255.255.0Hello interval: 10 secondsRouter Priority: 1Router Dead Interval: 40 secondsDesignated Router: 10.1.64.1Backup Designated Router: 10.1.64.2

Active Neighbor: 10.1.0.26

RouterA is theDesignated Routerfor this network.


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4 - 12Rev. 10.41

Flooding LSAs in a Link State Update Packet: 1

RouterA



RouterA and RouterB are adjacent, with three LSAs in their synchronizeddatabases. When RouterB detects a new neighbor on one of its OSPFinterfaces, the routers begin the exchange of messages that willsynchronize their link-state databases.

ID: 10.1.0.25

RouterBRouterC Link State Update

Link State Request

DB Description

3

Hello

OSPF Area 1.0.0.0 Networks:VLAN 30: 10.1.30.1/24VLAN 40: 10.1.40.1/24VLAN 64: 10.1.64.2/24VLAN 65: 10.1.65.2/24Loop 0: 10.1.0.26/32


n a e c : . . .: . . .

13 3


RouterA



ID: 10.1.0.25RouterBs existin ad acenc with RouterA re uires it to


Link State Request

DB Description

3

Hello

encapsulate any new LSAs in a Link State Update packetthat it floods immediately over the network they share.RouterA does not request the new LSAs.

Link-state UpdatePacket



n a e c : . . .: . . .

16 16


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4 - 13Rev. 10.41


RouterA




ID: 10.1.0.25RouterBs existin ad acenc with RouterA re uires it to


Link State Request

DB Description

16

Hello

encapsulate any new LSAs in a Link State Update packetthat it floods immediately over the network they share.RouterA does not request the new LSAs.

Link-state UpdatePacket

After receipt of the new LSAs, each routerupdates its link-state database to includethem, and acknowledges their receipt.



n a e c : . . .: . . .

16 16

LSA Flooding in a Multi-access Network: 1When an OSPF router experiences a link state transition, it mustoriginate a new instance of its Router LSA. The router floods theadvertisement to adjacent neighbors on point-to-point networksusing the reserved multicast address 224.0.0.5 (AllSPFRouters).

As each neighbor receives the LSA, it immediately floods toa jacent neig ors using t e same muticast a ress. outersdo not flood LSAs onto networks without adjacent neighbors.


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4 - 14Rev. 10.41

LSA Flooding in a Multi-access Network: 2

When an OSPF router experiences a link state transition, it mustoriginate a new instance of its Router LSA. The router floods theadvertisement to adjacent neighbors on point-to-point networksusing the reserved multicast address 224.0.0.5 (AllSPFRouters).

As each neighbor receives the LSA, it immediately floods toMulti-access network

DR

a jacent neig ors using t e same muticast a ress. outersdo not flood LSAs onto networks without adjacent neighbors.

The multicast address to which LSAs are flooded on a multi-access network depends on the state of the router interfaceflooding the advertisements.

A non-Designated Router (non-DR) is adjacent to the DR andBackup DR. It floods LSAs onto the multi-access networkusing the multicast address 224.0.0.6 (AllDRouters). Only

BDR

Non-

DR 3

Non-

DR 2

Non-

DR 1

the DR and Backup DR process this update.

LSA Flooding in a Multi-access Network: 3When an OSPF router experiences a link state transition, it mustoriginate a new instance of its Router LSA. The router floods theadvertisement to adjacent neighbors on point-to-point networksusing the reserved multicast address 224.0.0.5 (AllSPFRouters).

As each neighbor receives the LSA, it immediately floods toMulti-access network

DR

a jacent neig ors using t e same muticast a ress. outersdo not flood LSAs onto networks without adjacent neighbors.

The multicast address to which LSAs are flooded on a multi-access network depends on the state of the router interfaceflooding the advertisements.

A non-Designated Router (non-DR) is adjacent to the DR andBackup DR. It floods LSAs onto the multi-access networkusing the multicast address 224.0.0.6 (AllDRouters). Only

BDR

Non-

DR 3

Non-

DR 2

Non-

DR 1

the DR and Backup DR process this update.

The DR is adjacent to all neighbors on the multi-accessnetwork. It floods updates to the multicast address224.0.0.5.


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4 - 15Rev. 10.41

Link State Advertisement Details: 1

Point-to-point network10.1.4.0/30

Router ID: 10.1.0.32Int. s1: 10.1.4.1/30Loop 0: 10.1.0.32/32Int. e1: 10.1.128.1/24

Each networks type is important for graphingpurposes. The type of information included in a RouterLSA is uni ue for each t e of network. Three of the

OSPF routers run a link-state algorithm against their

database entries to create a graph that represents allrouters and networks in the local OSPF area.

Stub network10.1.128.0/24


Router ID: 10.1.0.33Int. s1: 10.1.4.2/30Loop 0: 10.1.0.33/32Int. e1: 10.1.64.1/24

Transit network10.1.64.0/24

Router ID: 10.1.0.35Int. e1: 10.1.64.3/24Loop 0: 10.1.0.35/32Int. e2: 10.1.130.1/24

-

Router ID: 10.1.0.34Int. e1: 10.1.64.2/24Loop 0: 10.1.0.34/32Int. e2: 10.1.129.1/24

A transit network is a multi-access networkwith two or more connected routers. TheRouter LSA represents this network as Type 2.

A point-to-point network is represented in theRouter LSA as Type 1.

.network types supported by OSPF are illustrated inthe graphic. Stub network

10.1.0.33/32

network, such as Ethernet, with only oneattached router. It is also used to represent therouters loopback interface. The Router LSA

represents stub networks as Type 3.The DR for each multi-access transit network originatesa Network LSA that lists its connected routers.





Link State Advertisement Details: 2Area 1.0.0.0 Link State Database

Router LSA (Type 1)Link State ID: 10.1.0.32 Advertising Router: 10.1.0.32Number of Links: 3

Type: Pt -t o- Pt (1 ) L in k ID: 10 .1 .0.33 L ink Data: 10.1.4.1 Metr ic : 100Type: S tub (3) L ink ID: 10.1.0.32 L ink Data: 255.255.255.255 Metric: 1Type: Stub (3) L ink ID: 10.1.128.0 L ink Data: 255.255.255.0 Metric: 10

Link State ID: 10.1.0.33 Advertising Router: 10.1.0.33Number of Links: 3

Type: Pt -t o- Pt (1 ) L in k ID: 10 .1.0.32 Li nk Da ta : 10 .1 .4 .2 Met ric : 100Type: T rans it (2 ) L in k ID: 10.1.64 .3 L in k Data: 10 .1 .64 .1 Met ri c: 10Type: S tub (3) L ink ID: 10.1.0.33 L ink Data: 255.255.255.255 Metric: 1

Router LSA (Type 1)Link State ID: 10.1.0.34 Advertising Router: 10.1.0.34Number of Links: 3

Type: Trans it (2) L ink ID: 10.1.64.3 L ink Data: 10.1.64.2 Metric: 10Type: S tub (3) L ink ID: 10.1.0.34 L ink Data: 255.255.255.255 Metric: 1Type: Stub

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