CDRouter Support

A dual-stack router providing IPv6 connectivity via 6to4 tunnels over the IPv4 WAN

knowledge-base version 12.13


Dual-stack CPE devices typically enable IPv6 connectivity via native IPv6 connections on the WAN or via tunneling protocols that transmit encapsulated IPv6 packets over the IPv4 WAN. Protocols such as DHCPv6 (with and without prefix delegation), PPPoE (running DHCPv6 or autoconf for address resolution), autoconf, or static IPv6 addressing can be used to provide native IPv6 connectivity on the WAN, whereas the most common tunneling protocols are 6to4 and 6rd. This recipe focuses on 6to4, since it requires minimal configuration and is perhaps the most common mechanism for providing IPv6 addresses to dual-stack clients on the LAN. The basic premise is the same for 6rd, which is based on and very similar in design to 6to4. A dual-stack recipe based on a native IPv6 connection to the WAN can be found here.

6to4, as defined in RFC 3056, is a transition mechanism that provides IPv6 connectivity to remote sites via automatic IPv4 tunnels on the WAN. In 6to4 terminology, the CPE is a 6to4 router since it acts as the gateway between the customer’s IPv6 site and the IPv4 WAN. IPv6 packets originating at the customer site that are destined for native IPv6 hosts are tunneled by the CPE over the IPv4 WAN to a 6to4 relay server located at the anycast address of IPv6 packets destined for other 6to4 connected sites are tunneled over the IPv4 WAN directly to the associated 6to4 router. See our Application Note on 6to4 and 6rd for more information.

Testing dual-stack 6to4 enabled devices with CDRouter is straightforward. The physical setup is the same as it would be for testing an IPv4 only device - CDRouter connects via Ethernet or wireless to the LAN side of the DUT, and via Ethernet, ATM, or T1/E1 to the WAN side of the DUT. However, when testing a dual-stack 6to4 enabled device the logical test environment is quite different, as shown in the diagram below. The simulated WAN ISP is IPv4 only in this example. Access to other simulated IPv6 enabled network elements, such as the DNS server(s) and ACS, is provided by the 6to4 relay server and 6to4 routers.

The diagram and example configuration below assume DHCP for IPv4 connectivity on the WAN, and 6to4 for tunneled access to the native IPv6 WAN and other 6to4 islands. It is also assumed that the CPE is providing IPv6 addresses to all LAN clients via SLAAC (autoconf).

Test Setup

CDRouter Configuration

# -- IPv4 Configuration:

# WAN configuration
testvar wanInterface             eth2
testvar wanMode                  DHCP
testvar wanIspIp       
testvar wanIspAssignIp 
testvar wanNatIp       
testvar wanIspNextIp   
testvar wanIspMask     
testvar wanDnsServer   
testvar wanBackupDnsServer
testvar RemoteHost     

# LAN configuration
testvar lanInterface             eth1
testvar lanIp          
testvar lanMask        
testvar dhcpClientStart
testvar dhcpClientEnd  

# -- IPv6 Configuration:

testvar supportsIPv6             yes

# WAN configuration
testvar ipv6WanMode              6to4
testvar ipv6RelayServer
testvar ipv6RelayServerGlobal    3001:051a:cafe::6

# LAN configuration
testvar ipv6LanMode              autoconf
testvar ipv6LanIp                ::1
testvar ipv6LanSubnetId          1
testvar ipv6WanDnsServer         3001:51a:cafe::2
testvar ipv6WanBackupDnsServer   3001:51a:cafe::3

# other configuration options
testvar ipv6RemoteHost           3001:51a:cafe::1
testvar ipv6FreeNetworkStart     3001:cafe:1::
testvar ipv6FreeNetworkEnd       3001:cafe:ffff::
testvar ipv6FreeNetworkPrefixLen 64

In the above example the DUT’s global IPv6 address is expected to be 6to4 prefix : ipv6LanSubnetId : host ID portion of ipv6LanIp. In this particular example, assuming the 16-bit Site Level Aggregator (SLA) used by the DUT is simply 1, the expected global IPv6 address prefix for this configuration is:

6to4 prefix:ipv6LanSubnetId::/64 = 2002:c0c:c02:1::/64


  • CDRouter or CDRouter Multiport
  • The CDRouter IPv6 add-on module
  • Two dedicated Ethernet network interfaces
  • One dual-stack router with 6to4 support


  • Simple setup, great for a stand-alone test station
  • Allows 6to4 enabled devices to be tested in isolation
  • Perfect for debugging test failures and testing functionality in a dual-stack environment
  • Useful for ensuring IPv6 connectivity when IPv4 WAN connection renumbers
  • Allows IPv6 prefix calculations to be verified in a variety IPv4 scenarios
  • Can be used to ensure routing logic for native IPv6 and remote 6to4 sites is correct

Additional Information

Please see the CDRouter IPv6 User’s Guide for more information.



About CDRouter

CDRouter is made by QA Cafe, a technology company based in Portsmouth, NH.

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