Automatic 6to4 Tunnels
Unlike the antecedent two adit types we accept discussed, automated 6to4 tunnels are inherently
point-to-multipoint in nature. These tunnels amusement the basal IPv4 arrangement as an NBMA cloud.
In automated 6to4 tunnels, the adit operates on a per-packet base to abbreviate cartage to the
correct destination—thus its point-to-multipoint nature. These tunnels actuate the appropriate
destination abode by accumulation the IPv6 prefix with the globally altered destination 6to4 border
router’s IPv4 address, alpha with the 2002::/16 prefix, in this format:
2002:border-router-IPv4-address::/48
This prefix-generation adjustment leaves accession 16 $.25 in the 64-bit prefix for calculation networks
within a accustomed site.
Cisco IOS supports configuring alone one automated 6to4 adit on a accustomed router. Configuring
these tunnels is agnate to configuring the added tunnels ahead discussed, except that the tunnel
mode is configured application the adit approach ipv6ip 6to4 command. Also, the adit destination is
not absolutely configured for 6to4 tunnels because of the automated attributes of the per-packet
destination prefix assurance adjustment that 6to4 uses.
In accession to the basal adit configuration, the added footfall of accouterment for acquisition the desired
packets over the adit is additionally required. This is usually done application a changeless route. For example, to
route packets destined for prefix 2002::/16 over the tunnel0 6to4 adit interface, configure this
static route:
ipv6 avenue 2002::/16 adit 0
Example 20-15 and Figure 20-8 appearance a sample of a 6to4 adit and the routers’ added relevant
interfaces to tie calm the concepts of 6to4 tunneling. In the example, agenda that the Fast Ethernet
interfaces and the adit interface get the adventurous allocation of the prefix 2002:0a01:6401:: from the
Ethernet 0 interface’s IPv4 address, 10.1.100.1. For this blazon of adit to work, the adit source
interface charge be the affiliation to the alfresco world, in this case the Ethernet 2/0 interface.
Furthermore, anniversary Fast Ethernet interface area hosts affix is (and charge be) a altered IPv6
subnet with the 2002:0a01:6401 prefix.
796 Chapter 20: IP Version 6
Figure 20-8 Automated 6to4 Adit Topology
Example 20-15 Automated 6to4 Adit Configuration
crosby# appearance running-config
! achievement bare for brevity
interface FastEthernet0/0
description IPv6 bounded host arrangement interface 1 of 2
ipv6 abode 2002:0a01:6401:1::1/64
!
interface FastEthernet0/1
description IPv6 bounded host arrangement interface 2 of 2
ipv6 abode 2002:0a01:6401:2::1/64
!
interface Ethernet2/0
description Ethernet articulation to the alfresco world
ip abode 10.1.100.1 255.255.255.0
!
interface Tunnel0
no ip address
ipv6 abode 2002:0a01:6401::1/64
tunnel antecedent Ethernet 2/0
tunnel approach ipv6ip 6to4
!
ipv6 avenue 2002::/16 adit 0
IPv6 Host
2002:0A01:6401:1::FA18/64
Dual-Stack
Router ‘crosby’
2002:0A01:6401:1::/64
IPv4 Network
10.1.100.0/24
To Added Automated 6 to 4
Tunnel Routers
IPv6 Host
2002:0A01:6401:2::AB01/64
2002:0A01:6401:2::/64 Fa0/1
Fa0/0
Ethernet 2/0
10.1.100.1/24
Note: 10.1.100.1 = 0A01:6401 in Hex