Avaya GRE, NAT, RIPSO, BFE User Manual

BayRS Version 14.20

Part No. 308625-14.20 Rev 00 October 2000

600 Technology Park Drive Billerica, MA 01821-4130

Configuring GRE, NAT, RIPSO, and BFE Services

The information in this document is subject to change without notice. The statements, configurations, technical data, and recommendations in this document are believed to be accurate and reliable, but are presented without express or implied warranty. Users must take full responsibility for their applications of any products specified in this document. The information in this document is proprietary to Nortel Networks NA Inc.

The software described in this document is furnished under a license agreement and may only be used in accordance with the terms of that license. The software license agreement is included in this document.

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BCN and BLN are registered trademarks and ASN, BCC, BayRS, and BayStack are trademarks of Nortel Networks.

All other trademarks and registered trademarks are the property of their respective owners.

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Notwithstanding any other license agreement that may pertain to, or accompany the delivery of, this computer software, the rights of the United States Government regarding its use, reproduction, and disclosure are as set forth in the Commercial Computer Software-Restricted Rights clause at FAR 52.227-19.

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308625-14.20 Rev 00

Nortel Networks NA Inc. Software License Agreement

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iii

for the security of its own data and information and for maintaining adequate procedures apart from the Software to reconstruct lost or altered files, data, or programs.

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Preface

Text Conventions .............................................................................................................xvi

Acronyms ........................................................................................................................xvii

Related Publications ...................................................................................................... xviii

How to Get Help ..............................................................................................................xix

Chapter 1 Configuring GRE Tunnels

GRE Concepts and Terminology .................................................................................... 1-2

How GRE Tunneling Works ......................................................................................1-3

Example of Packet Handling in a GRE Tunnel ...................................................1-4

GRE Packet Headers .........................................................................................1-5

Requirements for GRE Tunnels Encapsulating IP Protocol ..................................... 1-7

Announce Policies .............................................................................................1-7

Accept Policies .................................................................................................. 1-8

Static Routes .....................................................................................................1-8

Number of Tunnels Configurable per Router ............................................................1-9

For IP and IPX ...................................................................................................1-9

For OSI ..............................................................................................................1-9

Creating a GRE Tunnel .................................................................................................1-10

Configuring the Local Tunnel End Point .................................................................1-10

Adding a Protocol to the Local Tunnel End Point ...................................................1-12

Adding an IP Protocol Interface .......................................................................1-12

Adding an IPX Protocol Interface .....................................................................1-13

Adding an IP or an IPX Protocol Interface .......................................................1-13

Adding an OSI Protocol Interface ....................................................................1-14

Configuring the Remote Tunnel End Point ............................................................. 1-16

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Using the BCC .......................................................................................................1-17

Step 1. Configuring a Remote Physical Interface ............................................1-17

Step 2. Configuring a Remote Logical Interface ..............................................1-17

Using Site Manager ................................................................................................1-19

Configuring a Remote End Point for IP or IPX .................................................1-19

Configuring a Remote End Point for OSI .........................................................1-20

Customizing a GRE Tunnel ........................................................................................... 1-21

Disabling and Reenabling a GRE Tunnel ...............................................................1-21

Disabling and Reenabling a Protocol on a GRE Tunnel .........................................1-22

Deleting a Protocol from a GRE Tunnel .................................................................1-24

Disabling and Reenabling a Remote Tunnel End Point ..........................................1-25

Deleting a Remote Tunnel End Point .....................................................................1-26

Deleting a GRE Tunnel .................................................................................................1-27

Chapter 2 Configuring Network Address Translation

NAT Concepts .................................................................................................................2-2

Unidirectional NAT ....................................................................................................2-3

Advantages ........................................................................................................ 2-3

Requirements ....................................................................................................2-4

For More Information About Unidirectional NAT ................................................2-4

Representing Multiple Hosts with a Single Address: SDPT and N-to-1 ............2-5

For More Information on SDPT and N-to-1 ........................................................2-6

Bidirectional (Multidomain) NAT ...............................................................................2-7

Advantages ........................................................................................................ 2-7

Requirements ....................................................................................................2-7

How DNS Server, DNS Client, and DNS Proxy Work with Bidirectional NAT ....2-8

For More Information on Bidirectional NAT ........................................................2-9

Translation Modes .................................................................................................. 2-10

Static Translation Mode ...................................................................................2-10

Dynamic Translation Mode ..............................................................................2-11

Examining How Different Types of NAT Work ...............................................................2-13

Unidirectional NAT ..................................................................................................2-14

Static Unidirectional Address Translation ........................................................2-14

Dynamic Unidirectional Address Translation ...................................................2-15

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Static Destination and Port Translation (SDPT) ...............................................2-20

Network Address Port Translation (N-to-1) ......................................................2-23

Bidirectional NAT ....................................................................................................2-26

Static Bidirectional Address Translation ...........................................................2-26

Dynamic Bidirectional Address Translation with Two Domains ........................ 2-28

Dynamic Bidirectional Address Translation with Three Domains .....................2-29

NAT Implementation Guidelines ...................................................................................2-32

NAT General Configuration Considerations ...........................................................2-32

Protocol Requirements and Compatibilities ...........................................................2-33

NAT Requires IP Forwarding ........................................................................... 2-33

OSPF and BGP Supported for Unidirectional NAT Only ..................................2-33

ISP Mode Not Supported by NAT .................................................................... 2-33

ECMP Mode Supported for Unidirectional NAT Only ....................................... 2-33

Compatibility of NAT and IPsec on a Router Interface .....................................2-34

Special Considerations for Configuring NAT SDPT for FTP ............................2-34

Special Considerations for Configuring NAT SDPT for TFTP ..........................2-34

Multiple Source Address Filters -- Order of Precedence for NAT Types ................2-35

Internet Control Message Protocol and Message Handling ...................................2-39

Starting NAT Services and Configuring Translations ....................................................2-40

Configuring Unidirectional NAT (Dynamic) .............................................................2-40

Using the BCC .................................................................................................2-40

Using Site Manager .........................................................................................2-45

Configuring Bidirectional NAT (Dynamic) ...............................................................2-50

Using the BCC .................................................................................................2-50

Using Site Manager .........................................................................................2-56

Where to Go Next ..................................................................................................2-64

Customizing NAT Global Parameters ...........................................................................2-65

Enabling and Disabling NAT on the Router ............................................................2-66

Configuring the Soloist Slot Mask ..........................................................................2-67

Logging NAT Messages .........................................................................................2-69

Enabling and Disabling the Dynamic Mapping Aging Timer ..................................2-71

Configuring the Dynamic Mapping Timeout Value .................................................2-72

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Customizing a NAT Interface ........................................................................................2-74

Adding NAT to an Interface ....................................................................................2-74

Disabling and Reenabling NAT on an Interface ......................................................2-77

Deleting NAT from an Interface ..............................................................................2-79

Configuring NAT Static Address Translation .................................................................2-80

Adding a Static Unidirectional Address Mapping ...................................................2-81

Adding a Static Bidirectional Address Mapping .....................................................2-84

Examples of Configuring Static Bidirectional NAT to Work with or

Independent of DNS Proxy on the NAT Router ...............................................2-87

Adding an SDPT Address and Port Mapping .........................................................2-89

Disabling and Reenabling a Static Address Mapping ............................................2-92

Deleting a Static Address Mapping ........................................................................2-93

Configuring NAT Dynamic Address Translation ............................................................2-95

Adding a Source Address Filter ............................................................................. 2-97

IP Address and Prefix Length Parameter ........................................................2-98

Domain Name Parameter ................................................................................2-98

Translation Pool Parameter .............................................................................. 2-98

Static Nexthop Address Parameter ..................................................................2-99

Unnumbered Circuit Name Parameter .............................................................2-99

Disabling and Reenabling a Source Address Filter ..............................................2-103

Deleting a Source Address Filter ......................................................................... 2-105

Adding a Translation Pool .....................................................................................2-106

Disabling and Reenabling a Translation Pool .......................................................2-109

Deleting a Translation Pool ...................................................................................2-111

Configuring NAT N-to-1 Translation ............................................................................2-113

Chapter 3 Configuring RIPSO on an IP Interface

RIPSO Concepts and Terminology .................................................................................3-2

Security Label Format ..............................................................................................3-3

Inbound IP Datagrams ............................................................................................. 3-4

Forwarded IP Datagrams .........................................................................................3-5

Originated IP Datagrams ..........................................................................................3-5

Unlabeled IP Datagrams ..........................................................................................3-5

Enabling and Disabling RIPSO ....................................................................................... 3-6

Specifying the IP Datagram Type for Stripping Security Options ....................................3-7

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Specifying the Outbound Datagram Type Requiring Security Labels ............................. 3-8

Specifying the Inbound Datagram Type Requiring Security Labels ................................3-9

Setting the Security Level for IP Datagrams .................................................................3-10

Choosing Authority Flags in Outbound Datagrams ......................................................3-11

Choosing Authority Flags in Inbound Datagrams .........................................................3-12

Supplying Implicit Labels for Unlabeled Inbound Datagrams ....................................... 3-13

Enabling and Disabling Default Labels for Unlabeled Outbound Datagrams ................3-14

Enabling and Disabling Error Labels for Outbound ICMP Error Datagrams .................3-15

RIPSO Example ...........................................................................................................3-16

Chapter 4 Connecting the Router to a Blacker Front End

Blacker Front End (BFE) Concepts and Terminology .....................................................4-2

BFE Addressing .............................................................................................................. 4-4

Configuring BFE Support ...............................................................................................4-5

Appendix A Site Manager Parameters

GRE Parameters ........................................................................................................... A-2

GRE Tunnel Parameters ......................................................................................... A-2

Remote Connection Parameters ............................................................................. A-4

NAT Parameters ............................................................................................................. A-7

NAT Global Parameters ........................................................................................... A-7

NAT Interface Parameters ..................................................................................... A-11

NAT Static Translation Parameters ........................................................................ A-12

Adding Static Translation Parameters ............................................................. A-16

NAT Dynamic Mapping Parameters ...................................................................... A-24

NAT Source Address Filter Parameters .......................................................... A-25

Adding Source Address Filter Parameters ..................................................... A-28

NAT Translation Pool Parameters ................................................................... A-31

Adding NAT Translation Pool Parameters ....................................................... A-32

RIPSO Parameters ...................................................................................................... A-34

Appendix B Sample Bidirectional NAT Configuration

Overview of Configuration Tasks ................................................................................... B-1

Sample Scenario ........................................................................................................... B-2

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Configuring Sample Bidirectional NAT Using the BCC .................................................. B-3

Information Used in Bidirectional NAT Configuration .............................................. B-3

Checking Address Translations ................................................................................... B-10

show nat domains (BCC) ...................................................................................... B-11

show nat mappings (BCC) .................................................................................... B-12

show nat translations (Technician Interface) ......................................................... B-13

Index

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Figures

Figure 1-1. Simple GRE Tunnel Components ............................................................1-3

Figure 1-2. GRE Tunnel Encapsulating the IP Protocol .............................................1-5

Figure 1-3. GRE Packet Headers ...............................................................................1-6

Figure 1-4. Detail of GRE Header ..............................................................................1-6

Figure 2-1. Static Unidirectional NAT Configuration .................................................2-14

Figure 2-2. Network Address Translation Example ..................................................2-16

Figure 2-3. NAT Detects the Source Address ..........................................................2-17

Figure 2-4. NAT Updates the Private/Public Translation Entry List ...........................2-18

Figure 2-5. NAT Replaces the Private Address with a Registered Source

Address .................................................................................................. 2-19

Figure 2-6. Sample Configuration for NAT SDPT .....................................................2-21

Figure 2-7. N-to-1 Translation (Part 1) ......................................................................2-24

Figure 2-8. N-to-1 Translation (Part 2) ......................................................................2-25

Figure 2-9. Static Bidirectional NAT Configuration ...................................................2-26

Figure 2-10. Bidirectional NAT with DNS Proxy ..........................................................2-28

Figure 2-11. Bidirectional NAT with Three Domains ...................................................2-30

Figure 2-12. Network Address Translations Associated with Figure 2-11 ..................2-31

Figure 2-13. Sample Translation Types and Address Ranges ....................................2-36

Figure 2-14. More Sample Translation Types and Address Ranges ..........................2-37

Figure 2-15. Non-overlapping Address Ranges .........................................................2-38

Figure 3-1. RIPSO Security Label ..............................................................................3-3

Figure 3-2. RIPSO Example .....................................................................................3-17

Figure 4-1. BFE Network Configuration .....................................................................4-2

Figure A-1. GRE Create Tunnels List Window ........................................................... A-2

Figure A-2. Create GRE Remote Connection Window .............................................. A-4

Figure A-3. IP Interface List Window ....................................................................... A-34

Figure B-1. Sample Configuration for Bidirectional NAT ............................................ B-2

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Tabl es

Table 2-1. Comparing NAT Types SDPT and N-to-1 .................................................2-5

Table 2-2. Sample Configuration for a Router Configured with NAT .......................2-22

Table 2-3. NAT Log Message Types ...................................................................... 2-69

Table 4-1. BFE X.25 Packet-Level Parameter Settings ............................................4-6

Table 4-2. BFE X.25 Network Service Record Parameter Settings .........................4-8

Table B-1. Information to Gather Before Configuring NAT ....................................... B-3

Table B-2. Available show nat Commands ............................................................. B-10

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Preface

This guide describes the following services and what you do to start and customize them on a Nortel Networks

• Generic Routing Encapsulation (GRE) tunnels

• Network Address Translation (NAT)

• Basic Revised IP Security Option (RIPSO) security labels

• Blacker front-end (BFE) device connections

You can use Site Manager to configure any of these services on a router. You can also use the Bay Command Console (BCC guide, you will find instructions for using both the BCC and Site Manager.

™

router:

™

) to configure GRE and NAT. In this

For instructions on how to start and use the BCC, see Using the Bay Command

Console (BCC); for instructions on how to start and use Site Manager, see Configuring and Managing Routers with Site Manager.

Before using this guide, you must complete the following procedures. For a new router:

• Install the router (see the installation guide that came with your router).

• Connect the router to the network and create a pilot configuration file (see

Make sure that you are running the latest version of Nortel Networks BayRS Site Manager software. For information about upgrading BayRS and Site Manager, see the upgrading guide for your version of BayRS.

308625-14.20 Rev 00

Quick-Starting Routers, Configuring BayStack Remote Access, or Connecting ASN Routers to a Network).

™

and

Configuring GRE, NAT, RIPSO, and BFE Services

Text Conventions

This guide uses the following text conventions:

angle brackets (< >) Indicate that you choose the text to enter based on the

description inside the brackets. Do not type the brackets when entering the command.

Example: If the command syntax is:

ping < ping 192.32.10.12

ip_address

, you enter:

bold text

Indicates command names and options and text that you need to enter.

Example: Enter

Example: Use the

show ip {alerts | routes}.

command.

dinfo

braces ({}) Indicate required elements in syntax descriptions

where there is more than one option. You must choose only one of the options. Do not type the braces when entering the command.

Example: If the command syntax is:

show ip {alerts | routes} show ip alerts or show ip routes

, you must enter either:

, but not both.

brackets ([ ]) Indicate optional elements in syntax descriptions. Do

not type the brackets when entering the command.

Example: If the command syntax is:

show ip interfaces [-alerts] show ip interfaces

, you can enter either:

show ip interfaces -alerts

italic text Indicates new terms, book titles, and variables in

command syntax descriptions. Where a variable is two or more words, the words are connected by an underscore.

xvi

Example: If the command syntax is:

show at <

valid_route

is one variable and you substitute one value

for it.

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Preface

screen text Indicates system output, for example, prompts and

system messages.

Acronyms

Example:

Set Trap Monitor Filters

separator ( > ) Shows menu paths.

Example: Protocols > IP identifies the IP option on the Protocols menu.

vertical line (

) Separates choices for command keywords and

arguments. Enter only one of the choices. Do not type the vertical line when entering the command.

Example: If the command syntax is:

show ip {alerts | routes} show ip alerts

show ip routes

, you enter either:

This guide uses the following acronyms::

ACC access control center

BFE Blacker front end

BCN Backbone Concentrator Node

, but not both.

BGP Border Gateway Protocol

BLN Backbone Link Node

DCE data communication equipment

FTP File Transfer Protocol

GRE Generic Routing Encapsulation

HTTP HyperText Transfer Protocol

ICMP Internet Control Message Protocol

IP Internet Protocol

IPX Internetwork Packet Exchange

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Configuring GRE, NAT, RIPSO, and BFE Services

ITU-T International Telecommunication

Union-Telecommunication Standardization Sector (formerly CCITT)

KDC key distribution center

MAC media access control

NAT Network Address Translation or

Network Address Translator

OSPF Open Shortest Path First

RIP Routing Information Protocol

RIPSO Revised IP Security Option

SAP Service Advertising Protocol

SDPT Static Destination and Port Translation

TCP Transmission Control Protocol

TFTP Trivial File Transfer Protocol

UDP User Datagram Protocol

VPN virtual private network

WAN wide area network

Related Publications

For more information about GRE, NAT, and other IP services, refer to the following publications:

• Reference for BCC IP show commands

(Nortel Networks part number 308603-14.00 Rev 00)

Provides descriptions of all commands that display GRE and NAT configuration and statistical data.

• Configuring IP, ARP, RARP, RIP, and OSPF Services

(Nortel Networks part number 308627-14.00 Rev 00)

Provides a description of IP, ARP, RARP, RIP, and OSPF services and instructions for configuring them.

xviii

commands for IP services, including the

show

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• Configuring IP Exterior Gateway Protocols (BGP and EGP)

(Nortel Networks part number 308628-14.00 Rev 00)

Provides a description of Border Gateway Protocol (BGP) and Exterior Gateway Protocol (EGP) services and instructions for configuring them.

You can print selected technical manuals and release notes free, directly from the Internet. Go to the support.baynetworks.com/library/tpubs/ URL. Find the product for which you need documentation. Then locate the specific category and model or version for your hardware or software product. Use Adobe Acrobat Reader to open the manuals and release notes, search for the sections you need, and print them on most standard printers. Go to Adobe Systems at www.adobe.com to download a free copy of Acrobat Reader.

You can purchase selected documentation sets, CDs, and technical publications through the Internet at the www1.fatbrain.com/documentation/nortel/ URL.

How to Get Help

If you purchased a service contract for your Nortel Networks product from a distributor or authorized reseller, contact the technical support staff for that distributor or reseller for assistance.

Preface

If you purchased a Nortel Networks service program, contact one of the following Nortel Networks Technical Solutions Centers:

Technical Solutions Center Telephone

EMEA (33) (4) 92-966-968

North America (800) 2LANWAN or (800) 252-6926

Asia Pacific (61) (2) 9927-8800

China (800) 810-5000

An Express Routing Code (ERC) is available for many Nortel Networks products and services. When you use an ERC, your call is routed to a technical support person who specializes in supporting that product or service. To locate an ERC for your product or service, go to the www12.nortelnetworks.com/ URL and click ERC at the bottom of the page.

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xix

Chapter 1

Configuring GRE Tunnels

This chapter provides information about Generic Routing Encapsulation (GRE) tunnels and instructions for configuring them. It includes the following sections:

Topic Page

GRE Concepts and Terminology

Creating a GRE Tunnel 1-10

Customizing a GRE Tunnel 1-21

Deleting a GRE Tunnel 1-27

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GRE Concepts and Terminology

Generic Routing Encapsulation (GRE) is a protocol that allows transport of non-IP traffic through IP-based systems. GRE, which is defined in RFCs 1701 and 1702, encapsulates Internet Protocol (IP) and other layer 3 protocols to enable data transmission through an IP tunnel. This tunneling mechanism allows:

• Transport of non-IP traffic through intermediate systems that support only IP

• Creation of a virtual private network (VPN) that uses the Internet as a section

of your own private network

• Communication between subnetworks with unregistered or discontiguous network addresses

A tunnel is a virtual point-to-point connection. It has as its end points the IP addresses of two router IP interfaces, one serving as the source, the other serving as the destination. When using GRE, remember that:

• This protocol is slower than native routing because packets require additional processing.

• IP fragmentation of the packet can occur due to extra bytes introduced by encapsulation.

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• Troubleshooting the physical link when problems occur is difficult.

GRE tunnels support encapsulation of the following protocols:

• IP - Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP)

• Internet Protocol Exchange (IPX) and IPX RIP/Service Advertising Protocol (SAP)

• Open Systems Interconnection (OSI)

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How GRE Tunneling Works

A simple point-to-point GRE tunnel terminates at router interfaces at each end of the tunnel (Figure 1-1 more logical addresses. For IP and IPX protocols, at each tunnel end point there is one logical address for each protocol configured for encapsulation over the tunnel. Because the concept of an interface address does not exist in OSI, only one IP address is required per router.

Configuring GRE Tunnels

). Each interface has a physical address and may have one or

Remote logical

host interface

Host

Router

Remote physical

router interface

IP0095A

Host

Router

Local physical

router interface

Local logical

host interface

GRE tunnel

Figure 1-1. Simple GRE Tunnel Components

The physical address, which is always an IP address, is visible to the devices making up the intervening network cloud. The logical addresses are not visible to the devices that make up the intervening network cloud. They are private addresses, visible only to the networks on either side of the tunnel.

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The GRE tunnel can use any IP interface configured on the router as a physical end point. To maximize the robustness of the tunnel, use a circuitless IP address as a tunnel’s physical end point whenever possible. Because a circuitless IP address is associated with the whole router, not one physical interface, the tunnel operates as long as any slot that has a working IP interface stays up. (For instructions on configuring a circuitless interface, see Configuring IP, ARP, RARP, RIP, and OSPF Services.)

Example of Packet Handling in a GRE Tunnel

The following steps explain how GRE tunneling takes place. The example describes a GRE tunnel encapsulating IP or IPX (refer to Figure 1-2

The router interface on router 1 receives a packet from host 1, looks up the packet’s destination address in its IP routing table, and determines that the next hop to the destination address is the remote end of a GRE tunnel. The router interface queues the packet at the tunnel interface for GRE encapsulation.

Router 1 adds a GRE header to the packet and sends the packet to IP.

IP looks up the route to the remote tunnel end point and sends the GRE-encapsulated packet to the appropriate next-hop address.

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The remote tunnel interface on router 2 removes the outer IP header and the GRE header.

The remote router interface looks up the packet’s destination address in its routing table and chooses the next hop to reach host 2.

The same process would take place for IPX.

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Configuring GRE Tunnels

Host

Key

interface

10.0.0.1

8.0.0.2

Data

Router 1

Router

Tunnel

interface

MAC header Source IP address Destination IP address

Transport protocol

Passenger protocol

Internet/Intranet

11.0.0.10

11.0.0.20

10.0.0.1

8.0.0.2

Data

MAC header Source IP address Destination IP address GRE header Source IP address Destination address

Router 2

Tunnel

interface

MAC header

Source IP address

Destination IP address

Router

interface

10.0.0.1

8.0.0.2

Data

Host

Figure 1-2. GRE Tunnel Encapsulating the IP Protocol

GRE Packet Headers

The previous example followed the path of a GRE packet as it traversed the tunnel, explaining its handling. Here is some detail about what occurs with the headers of such a GRE packet. A GRE packet has the following headers (Figure 1-3

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IP0064A

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Configuring GRE, NAT, RIPSO, and BFE Services

IP delivery header

GRE header

Payload packet

IP0110A

Figure 1-3. GRE Packet Headers

The outermost (delivery) header is an IP header with protocol type 0x47 (GRE). For a packet arriving at the router through a tunnel, the destination address is an IP interface that the network administrator configures as the GRE tunnel remote end point. The next header is the GRE header (Figure 1-4 payload. The payload could be IP, IPX, or OSI, in which case it would contain an identifying header of the protocol type.

). The last header is the

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0123 01234567890123456789012345678901

Recur Flag Ver C

K S s

Key (optional)

Sequence number (optional)

Routing (optional)

Protocol type

Offset (optional)Checksum (optional)

IP0111A

Figure 1-4. Detail of GRE Header

For a more complete description of the GRE header, see RFC 1701.

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Configuring GRE Tunnels

Requirements for GRE Tunnels Encapsulating IP Protocol

If you are using GRE tunneling to encapsulate the IPX or OSI protocol,

Note:

skip this section. The requirements discussed below do not apply to tunnels encapsulating IPX or OSI.

Before configuring a tunnel encapsulating IP, you should be aware of a limitation inherent in the use of all tunnels, including GRE tunnels. A tunnel is a virtual point-to-point connection between two routers that are actually several hops apart. This point-to-point connection can hide the real distance between the routers from portions of the network, leading to unintended, suboptimal routing decisions and in some cases, to routing loops.

In particular, if a router at one end of a tunnel determines that the best route to the remote physical end point of the tunnel is through the tunnel itself, a loop, internal to the router, occurs and prevents the tunnel from operating. You must configure one of the following at each end of the tunnel to prevent routing loops:

• Announce policy

• Accept policy

• Static route

The best choice depends on the network topology to which it is applied.

When configuring a tunnel with IP encapsulation, you must implement

Note:

an announce or accept policy or a static route at each end of the tunnel for the tunnel to operate correctly.

Announce Policies

An announce policy governs the advertisement of routing information. When preparing a routing advertisement, IP consults its announce policies to determine whether to advertise the route. For GRE tunneling, you can configure an announce policy for each routing protocol (RIP, OSPF, BGP) configured on the logical tunnel interface to block the advertisement of a range of network addresses that contains the tunnel’s local physical interface address. For information about configuring RIP and OSPF announce policies, see Configuring IP, ARP, RARP, RIP, and OSPF Services. For information about configuring BGP announce policies, see Configuring IP Exterior Gateway Protocols (BGP and EGP).

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The disadvantage of using an announce policy is that it prevents the advertisement of other subnets within the blocked range. Depending on the network topology, this configuration may not be desirable.

Accept Policies

An accept policy governs the addition of new routes to the routing tables. For GRE tunneling, you can configure an accept policy for each routing protocol (RIP, OSPF, BGP) configured on the logical tunnel interface to block the receipt of advertisements from a range of network addresses that contains the tunnel’s remote physical interface address. For information about configuring RIP and OSPF accept policies, see Configuring IP, ARP, RARP, RIP, and OSPF Services. For information about configuring BGP accept policies, see Configuring IP Exterior Gateway Protocols (BGP and EGP).

The disadvantage of using an accept policy is that it prevents the receipt of advertisements of subnets contained in the blocked range. Depending on the network topology, this configuration may not be desirable.

Static Routes

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A static route is a route configuration that designates a specific router within the intervening network cloud as the next hop to the remote physical tunnel end point. Because static routes take precedence over routes that the router learns dynamically from routing protocols, this configuration forces the router to direct packets through the cloud to reach the tunnel’s remote physical address.

The disadvantage of using a static route is that it is fixed. If the path through the chosen next hop to the remote tunnel end point goes down, the tunnel goes down as well until you manually reconfigure the static route. Similarly, even if the path through the chosen next hop becomes more costly than the path through some other attached router, the tunnel continues to use the more costly path unless you manually intervene.

Note:

When configuring a static route, be careful not to inadvertently create a

loop.

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Number of Tunnels Configurable per Router

The number of GRE tunnels you can configure on a router varies, depending on the type of protocol being encapsulated.

For IP and IPX

You can create up to 64 GRE tunnels on one router; each GRE tunnel can have multiple end points. You can configure up to 256 remote tunnel end points distributed over the configured GRE tunnels for IP and IPX.

For OSI

GRE point-to-point and point-to-multipoint tunnels are viewed by OSI as point-to-point subnetworks as defined by ISO 10589. Each GRE tunnel appears as a single OSI interface. Configure GRE tunnels for OSI traffic within the following guidelines:

• Each router interface can support one GRE tunnel configured with OSI.

• A single 32 Mb router slot can support a maximum of 48 interfaces.

Configuring GRE Tunnels

• The maximum number of end points per tunnel is 150.

Theoretically, a single slot could support 48 interfaces, each of which could be a point-to-multipoint configuration. OSI would treat this configuration as 48 groups of point-to-point subnetworks with each subnetwork having an adjacency. (An adjacent router is the next hop on the path toward the destination.) Each adjacency would have its own state machine, and flooding of data would be resource intensive because datagrams would need to be propagated along each adjacency. Such a configuration would have implications for buffer and memory usage.

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Creating a GRE Tunnel

To create a tunnel:

1. Configure the local tunnel end point.

Add one or more protocols (IP, IPX, or OSI) to the local tunnel end point.

3. Configure the remote tunnel end point.

For instructions, see:

Topic Page

onfiguring the Local Tunnel End Point 1-10

Adding a Protocol to the Local Tunnel End Point 1-12

Configuring the Remote Tunnel End Point 1-16

Configuring the Local Tunnel End Point

When you create a GRE tunnel, you assign the tunnel a name and an IP address. The IP address is the router interface used as the local physical end point for this tunnel. The IP address must be that of an existing physical router IP interface or the circuitless address. To maximize the robustness of the tunnel, use a circuitless IP address as a tunnel’s physical end point whenever possible. (For instructions on configuring a circuitless IP interface, see Configuring IP, ARP, RARP, RIP, and OSPF Services.)

Using the BCC

1-10

This IP address is visible to the network cloud that the tunnel passes through.

To configure the local tunnel end point of a GRE tunnel:

1. Navigate to the box or stack prompt and enter:

tunnels

The tunnels prompt appears.

2. Navigate to the tunnels prompt (for example, box; tunnels) and enter the

following command:

gre name

<name>

local-address

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Avaya GRE, NAT, RIPSO, BFE User Manual

Configuring GRE, NAT, RIPSO, and BFE Services

Contents

Figures

Tabl es

Preface

Text Conventions

Acronyms

Related Publications

How to Get Help

GRE Concepts and Terminology

How GRE Tunneling Works

Example of Packet Handling in a GRE Tunnel

GRE Packet Headers

Requirements for GRE Tunnels Encapsulating IP Protocol

Announce Policies

Accept Policies

Static Routes

Number of Tunnels Configurable per Router

For IP and IPX

For OSI

Creating a GRE Tunnel

Configuring the Local Tunnel End Point