| IPv6 Network - The DNS Problem |
IPv6 Network - The DNS Problem
Just like IPv4, IPv6 uses the Domain Name System (DNS) to resolve host names into addresses that make the desired communication possible. Requesting information from a DNS server is also nearly identical in IPv4, except for one problem: in IPv6, there aren’t really any mechanisms to automatically discover the addresses of the local DNS servers. In theory, IPv6 hosts can autoconfigure addresses and other information in two ways: stateless and stateful.
Stateless autoconfiguration is the mechanism defined
in RFC 2462 we’ve been discussing so far. But rather than supply the
address prefixes themselves, routers can also indicate that hosts
should use a stateful mechanism to configure addresses and/or other
configuration information by setting the “managed address
configuration” and “other stateful configuration” flags. The stateful
mechanism in question is the Dynamic Host Configuration Protocol
modified for IPv6 (DHCPv6), defined in RFC 3315. This RFC was published
only in July 2003, and at the time of this writing, DHCPv6 hadn’t found
its way into the operating systems that are discussed here, except for
Red Hat ES 4. See Chapter 8 for examples of how to use DHCPv6. Because
DHCPv6 is currently the only way that is defined for automatically
configuring IPv6 DNS addresses, current OSs simply lack this
capability. And, as working with addresses exclusively isn’t unlike
cruel and unusual punishment, an IPv6 hosts must either also run IPv4
and discover IPv4 DNS addresses through DHCP(v4) or the IPv6 DNS
addresses must be configured manually. In MacOS X Panther, the
graphical TCP/IP configuration panes accept IPv6 addresses, as
mentioned earlier. Under FreeBSD and Linux, this is done by adding a
line like the following to the file
/etc/resolv.conf: nameserver 2002:a00:1:5353:20a:95ff:fef5:246e
Note that the above isn’t the address for a
functioning nameserver (and an illegal 6to4 address to boot). Under
MacOS, the resolv.conf file is a symbolic link to the file
/var/run/resolv.conf. You can modify this file, but it’s removed and
overwritten by the system whenever network connectivity changes. Under
Windows XP, it’s possible to configure a nameserver with the netsh
interface ipv6 add dns command, but this doesn’t result in Windows
actually querying the thus configured IPv6 DNS servers. See Chapter 5
for more information on putting IPv6 information in the DNS and running
an IPv6-capable nameserver.
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