Interface and Hardware Component Configuration Guide, Cisco IOS Release 15S
IPv6 GRE Tunnels in CLNS Networks
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IPv6 GRE Tunnels in CLNS Networks

IPv6 GRE Tunnels in CLNS Networks

GRE tunneling of IPv4 and IPv6 packets through CLNS networks enables Cisco CTunnels to interoperate with networking equipment from other vendors.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

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.

Information About IPv6 GRE Tunnels in CLNS Networks

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.

GRE CLNS Tunnel Support for IPv4 and IPv6 Packets

GRE tunneling of IPv4 and IPv6 packets through CLNS networks enables Cisco CLNS Tunnels (CTunnels) to interoperate with networking equipment from other vendors. This feature provides compliance with RFC 3147.

The optional GRE services defined in header fields, such as checksums, keys, and sequencing, are not supported. Any packet received requesting such services will be dropped.

Configuration Examples for IPv6 GRE Tunnels in CLNS Networks

Example: Configuring CTunnels in GRE Mode to Carry IPv6 Packets in CLNS

The following example configures a GRE CTunnel running both IS-IS and IPv6 traffic between Router A and Router B in a CLNS network. The ctunnel mode gre command allows tunneling between Cisco and third-party networking devices and carries both IPv4 and IPv6 traffic.

The ctunnel mode gre command provides a method of tunneling that is compliant with RFC 3147 and allows tunneling between Cisco equipment and third-party networking devices.

Router A

ipv6 unicast-routing 
clns routing 
interface ctunnel 102 
 ipv6 address 2001:DB8:1111:2222::1/64
 ctunnel destination 49.0001.2222.2222.2222.00 
 ctunnel mode gre
interface Ethernet0/1 
 clns router isis 
router isis 
 net 49.0001.1111.1111.1111.00 

Router B

ipv6 unicast-routing 
clns routing 
interface ctunnel 201 
 ipv6 address 2001:DB8:1111:2222::2/64 
 ctunnel destination 49.0001.1111.1111.1111.00 
 ctunnel mode gre
interface Ethernet0/1 
 clns router isis 
router isis 
 net 49.0001.2222.2222.2222.00 

To turn off GRE mode and restore the CTunnel to the default Cisco encapsulation routing only between endpoints on Cisco equipment, use either the no ctunnel mode command or the ctunnel mode cisco command. The following example shows the same configuration modified to transport only IPv4 traffic.

Additional References

Related Documents

Related Topic

Document Title

IPv6 addressing and connectivity

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

MIBs

MIB

MIBs Link

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http:/​/​www.cisco.com/​go/​mibs

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 IPv6 GRE Tunnels in CLNS Networks

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 3 Feature Information for IPv6 GRE Tunnels in CLNS Networks

Feature Name

Releases

Feature Information

CLNS Support for GRE Tunneling of IPv4 and IPv6

12.2(25)S

12.2(33)SRA

12.3(7)T

GRE tunneling of IPv4 and IPv6 packets through CLNS networks enables Cisco CTunnels to interoperate with networking equipment from other vendors.

The following commands were introduced or modified: ctunnel mode.