ISATAP Tunnel Support for IPv6

ISATAP is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a NBMA link layer for IPv6

Information About ISATAP Tunnel Support for IPv6

Overlay Tunnels for IPv6

Overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure (a core network or the figure below). By using overlay tunnels, you can communicate with isolated IPv6 networks without upgrading the IPv4 infrastructure between them. Overlay tunnels can be configured between border devices or between a border device and a host; however, both tunnel endpoints must support both the IPv4 and IPv6 protocol stacks. IPv6 supports the following types of overlay tunneling mechanisms:

  • Manual

  • Generic routing encapsulation (GRE)

  • IPv4-compatible

  • 6to4

  • Intrasite Automatic Tunnel Addressing Protocol (ISATAP)

Figure 1. Overlay Tunnels

Note
Overlay tunnels reduce the maximum transmission unit (MTU) of an interface by 20 octets (assuming that the basic IPv4 packet header does not contain optional fields). A network that uses overlay tunnels is difficult to troubleshoot. Therefore, overlay tunnels that connect isolated IPv6 networks should not be considered a final IPv6 network architecture. The use of overlay tunnels should be considered as a transition technique toward a network that supports both the IPv4 and IPv6 protocol stacks or just the IPv6 protocol stack.

Use the table below to help you determine which type of tunnel that you want to configure to carry IPv6 packets over an IPv4 network.

Table 1. Suggested Usage of Tunnel Types to Carry IPv6 Packets over an IPv4 Network

Tunneling Type

Suggested Usage

Usage Notes

Manual

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6 packets only.

GRE- and IPv4- compatible

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6, Connectionless Network Service (CLNS), and many other types of packets.

IPv4- compatible

Point-to-multipoint tunnels.

Uses the ::/96 prefix. We do not recommend using this tunnel type.

6to4

Point-to-multipoint tunnels that can be used to connect isolated IPv6 sites.

Sites use addresses from the 2002::/16 prefix.

6RD

IPv6 service is provided to customers over an IPv4 network by using encapsulation of IPv6 in IPv4.

Prefixes can be from the SP’s own address block.

ISATAP

Point-to-multipoint tunnels that can be used to connect systems within a site.

Sites can use any IPv6 unicast addresses.

Individual tunnel types are discussed in detail in this document. We recommend that you review and understand the information about the specific tunnel type that you want to implement. When you are familiar with the type of tunnel you need, see the table below for a summary of the tunnel configuration parameters that you may find useful.

Table 2. Tunnel Configuration Parameters by Tunneling Type

Tunneling Type

Tunnel Configuration Parameter

Tunnel Mode

Tunnel Source

Tunnel Destination

Interface Prefix or Address

Manual

ipv6ip

An IPv4 address, or a reference to an interface on which IPv4 is configured.

An IPv4 address.

An IPv6 address.

GRE/IPv4

gre ip

An IPv4 address.

An IPv6 address.

IPv4- compatible

ipv6ip auto-tunnel

Not required. These are all point-to-multipoint tunneling types. The IPv4 destination address is calculated, on a per-packet basis, from the IPv6 destination.

Not required. The interface address is generated as ::tunnel-source /96.

6to4

ipv6ip 6to4

An IPv6 address. The prefix must embed the tunnel source IPv4 address.

6RD

ipv6ip 6rd

An IPv6 address.

ISATAP

ipv6ip isatap

An IPv6 prefix in modified eui-64 format. The IPv6 address is generated from the prefix and the tunnel source IPv4 address.

ISATAP Tunnels

ISATAP is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a NBMA link layer for IPv6. ISATAP is designed for transporting IPv6 packets within a site where a native IPv6 infrastructure is not yet available; for example, when sparse IPv6 hosts are deployed for testing. ISATAP tunnels allow individual IPv4 or IPv6 dual-stack hosts within a site to communicate with other such hosts on the same virtual link, basically creating an IPv6 network using the IPv4 infrastructure.

The ISATAP router provides standard router advertisement network configuration support for the ISATAP site. This feature allows clients to automatically configure themselves as they would do if they were connected to a GigabitEthernet or FastEthernet. It can also be configured to provide connectivity out of the site. ISATAP uses a well-defined IPv6 address format composed of any unicast IPv6 prefix (/64), which can be link local, or global (including 6to4 prefixes), enabling IPv6 routing locally or on the Internet. The IPv4 address is encoded in the last 32 bits of the IPv6 address, enabling automatic IPv6-in-IPv4 tunneling.

Although the ISATAP tunneling mechanism is similar to other automatic tunneling mechanisms, such as IPv6 6to4 tunneling, ISATAP is designed for transporting IPv6 packets within a site, not between sites.

ISATAP uses unicast addresses that include a 64-bit IPv6 prefix and a 64-bit interface identifier. The interface identifier is created in modified EUI-64 format in which the first 32 bits contain the value 000:5EFE to indicate that the address is an IPv6 ISATAP address. The table below describes an ISATAP address format.

Table 3. IPv6 ISATAP Address Format

64 Bits

32 Bits

32 Bits

link local or global IPv6 unicast prefix

0000:5EFE

IPv4 address of the ISATAP link

As shown in the table above, an ISATAP address consists of an IPv6 prefix and the ISATAP interface identifier. This interface identifier includes the IPv4 address of the underlying IPv4 link. The following example shows what an actual ISATAP address would look like if the prefix is 2001:DB8:1234:5678::/64 and the embedded IPv4 address is 10.173.129.8. In the ISATAP address, the IPv4 address is expressed in hexadecimal as 0AAD:8108:

2001:DB8:1234:5678:0000:5EFE:0AAD:8108

How to Configure ISATAP Tunnel Support for IPv6

Configuring ISATAP Tunnels

Before you begin

The tunnel source command used in the configuration of an ISATAP tunnel must point to an interface with an IPv4 address configured. The ISATAP IPv6 address and prefix (or prefixes) advertised are configured as for a native IPv6 interface. The IPv6 tunnel interface must be configured with a modified EUI-64 address because the last 32 bits in the interface identifier are constructed using the IPv4 tunnel source address.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface tunnel tunnel-number
  4. ipv6 address {ipv6-address / prefix-length | prefix-name sub-bits /prefix-length
  5. no ipv6 nd ra suppress
  6. tunnel source {ip-address | interface-type interface-number }
  7. tunnel mode ipv6ip [6rd | 6to4 | auto-tunnel | isatap

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Router# configure terminal

Enters global configuration mode.

Step 3

interface tunnel tunnel-number

Example:


Router(config)# interface tunnel 1

Specifies a tunnel interface and number, and enters interface configuration mode.

Step 4

ipv6 address {ipv6-address / prefix-length | prefix-name sub-bits /prefix-length

Example:


Router(config-if)# ipv6 address 2001:DB8:6301::/64 eui-64

Specifies the IPv6 address assigned to the interface and enables IPv6 processing on the interface.

Step 5

no ipv6 nd ra suppress

Example:


Router(config-if)# no ipv6 nd ra suppress

Sending of IPv6 router advertisements is disabled by default on tunnel interfaces. This command reenables the sending of IPv6 router advertisements to allow client autoconfiguration.

Step 6

tunnel source {ip-address | interface-type interface-number }

Example:


Router(config-if)# tunnel source gigabitethernet 1/0/1

Specifies the source interface type and number for the tunnel interface.

Note

 

The interface type and number specified in the tunnel source command must be configured with an IPv4 address.

Step 7

tunnel mode ipv6ip [6rd | 6to4 | auto-tunnel | isatap

Example:


Router(config-if)# tunnel mode ipv6ip isatap

Specifies an IPv6 overlay tunnel using a ISATAP address.

  • The auto-tunnel keyword is not supported on Cisco ASR 1000 series routers.

Configuration Examples for ISATAP Tunnel Support for IPv6

Example: Configuring ISATAP Tunnels

The following example shows the tunnel source defined on GigabitEthernet 0/0/0 and the tunnel mode command used to configure the ISATAP tunnel. Router advertisements are enabled to allow client autoconfiguration. 


ipv6 unicast-routing
interface tunnel 1
 tunnel source Gigabitethernet 0/0/0
 tunnel mode ipv6ip isatap
 ipv6 address 2001:DB8::/64 eui-64
 no ipv6 nd ra suppress
 exit

Additional References

Related Documents

Related Topic

Document Title

IPv6 addressing and connectivity

Cisco IOS IPv6 Configuration Guide

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

IPv6 commands

Cisco IOS IPv6 Command Reference

Cisco IOS IPv6 features

Cisco IOS IPv6 Feature Mapping

Standards and RFCs

Standard/RFC

Title

RFCs for IPv6

IPv6 RFCs

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for ISATAP Tunnel Support for IPv6

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 4. Feature Information for ISATAP Tunnel Support for IPv6

Feature Name

Releases

Feature Information

ISATAP Tunnel Support for IPv6

Cisco IOS XE Release 2.1

ISATAP is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a NBMA link layer for IPv6.

The following commands were introduced or modified: ipv6 nd ra suppress , tunnel mode ipv6ip , tunnel source .