IPv6 Automatic 6to4 Tunnels

This feature provides support for IPv6 automatic 6to4 tunnels. An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks.

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Information About IPv6 Automatic 6to4 Tunnels

Automatic 6to4 Tunnels

An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks. The key difference between automatic 6to4 tunnels and manually configured tunnels is that the tunnel is not point-to-point; it is point-to-multipoint. In automatic 6to4 tunnels, routers are not configured in pairs because they treat the IPv4 infrastructure as a virtual nonbroadcast multiaccess (NBMA) link. The IPv4 address embedded in the IPv6 address is used to find the other end of the automatic tunnel.

An automatic 6to4 tunnel may be configured on a border router in an isolated IPv6 network, which creates a tunnel on a per-packet basis to a border router in another IPv6 network over an IPv4 infrastructure. The tunnel destination is determined by the IPv4 address of the border router extracted from the IPv6 address that starts with the prefix 2002::/16, where the format is 2002:border-router-IPv4-address ::/48. Following the embedded IPv4 address are 16 bits that can be used to number networks within the site. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks. 6to4 tunnels are configured between border routers or between a border router and a host.

The simplest deployment scenario for 6to4 tunnels is to interconnect multiple IPv6 sites, each of which has at least one connection to a shared IPv4 network. This IPv4 network could be the global Internet or a corporate backbone. The key requirement is that each site have a globally unique IPv4 address; the Cisco software uses this address to construct a globally unique 6to4/48 IPv6 prefix. As with other tunnel mechanisms, appropriate entries in a Domain Name System (DNS) that map between hostnames and IP addresses for both IPv4 and IPv6 allow the applications to choose the required address.

How to Configure IPv6 Automatic 6to4 Tunnels

Configuring Automatic 6to4 Tunnels

Before you begin

With 6to4 tunnels, the tunnel destination is determined by the border router IPv4 address, which is concatenated to the prefix 2002::/16 in the format 2002:border-router-IPv4-address ::/48. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks.


Note

The configuration of only one IPv4-compatible tunnel and one 6to4 IPv6 tunnel is supported on a router. If you choose to configure both of those tunnel types on the same router, we strongly recommend that they do not share the same tunnel source.

The reason that a 6to4 tunnel and an IPv4-compatible tunnel cannot share an interface is that both of them are NBMA "point-to-multipoint" access links and only the tunnel source can be used to reorder the packets from a multiplexed packet stream into a single packet stream for an incoming interface. So when a packet with an IPv4 protocol type of 41 arrives on an interface, that packet is mapped to an IPv6 tunnel interface based on the IPv4 address. However, if both the 6to4 tunnel and the IPv4-compatible tunnel share the same source interface, the router is not able to determine the IPv6 tunnel interface to which it should assign the incoming packet.

IPv6 manually configured tunnels can share the same source interface because a manual tunnel is a "point-to-point" link, and both the IPv4 source and IPv4 destination of the tunnel are defined.

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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. tunnel source {ip-address | interface-t ype interface-number }
  6. tunnel mode ipv6ip [6rd | 6to4 | auto-tunnel | isatap
  7. exit
  8. ipv6 route [vrf vrf-name ] ipv6-prefix / prefix-length {ipv6-address | interface-type interface-number [ipv6-address ]} [nexthop-vrf [vrf-name1 | default ]] [administrative-distance ] [administrative-multicast-distance | unicast | multicast ] [next-hop-address ] [tag tag ]

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 3ffe:b00:c18:1::3/127

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

Step 5

tunnel source {ip-address | interface-t ype interface-number }

Example:


Router(config-if)# tunnel source loopback 1

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

Step 6

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

Example:


Router(config-if)# tunnel mode ipv6ip 6rd

Configures a static IPv6 tunnel interface.

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

Step 7

exit

Example:


Router(config-if) exit

Exits interface configuration mode, and enters global configuration mode.

Step 8

ipv6 route [vrf vrf-name ] ipv6-prefix / prefix-length {ipv6-address | interface-type interface-number [ipv6-address ]} [nexthop-vrf [vrf-name1 | default ]] [administrative-distance ] [administrative-multicast-distance | unicast | multicast ] [next-hop-address ] [tag tag ]

Example:


Router(config)# ipv6 route 2002::/16 tunnel 0

Configures a static route for the IPv6 6to4 prefix 2002::/16 to the specified tunnel interface.

Note 

When configuring a 6to4 overlay tunnel, you must configure a static route for the IPv6 6to4 prefix 2002::/16 to the 6to4 tunnel interface.

  • The tunnel number specified in the ipv6 route command must be the same tunnel number specified in the interface tunnel command.

Configuration Examples for IPv6 Automatic 6to4 Tunnels

Example: Configuring 6to4 Tunnels

The following example configures a 6to4 tunnel on a border router in an isolated IPv6 network. The IPv4 address is 192.168.99.1, which translates to the IPv6 prefix of 2002:c0a8:6301::/48. The IPv6 prefix is subnetted into 2002:c0a8:6301::/64 for the tunnel interface: 2002:c0a8:6301:1::/64 for the first IPv6 network, and 2002:c0a8:6301:2::/64 for the second IPv6 network. The static route ensures that any other traffic for the IPv6 prefix 2002::/16 is directed to tunnel interface 0 for automatic tunneling. 


interface GigabitEthernet0/0/0
 description IPv4 uplink
 ip address 192.168.99.1 255.255.255.0
!
interface GigabitEthernet1/0/0
 description IPv6 local network 1
 ipv6 address 2002:c0a8:6301:1::1/64 
!
interface GigabitEthernet2/0/0
 description IPv6 local network 2
 ipv6 address 2002:c0a8:6301:2::1/64 
!
interface Tunnel0
 description IPv6 uplink
 no ip address
 ipv6 address 2002:c0a8:6301::1/64 
 tunnel source GigabitEthernet0/0/0
 tunnel mode ipv6ip 6to4
!
ipv6 route 2002::/16 tunnel 0

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 Automatic 6to4 Tunnels

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 1. Feature Information for IPv6 Automatic 6to4 Tunnels

Feature Name

Releases

Feature Information

IPv6 Tunneling: Automatic 6to4 Tunnels

Cisco IOS XE Release 2.1

An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks.

The following commands were introduced or modified: tunnel mode ipv6ip , tunnel source .