Table of Contents
- Introduction
2. General Network Overview
3. BIND Extensions
4. Supporting IPv6 in the Kernel and in Network Binaries
5. IP6 Name Resolution
6. Configuring IPv6 DNS and DNSSEC
- Types of zones
- Main Configuration file
- Configuration file for domain
- Starting DNS Daemon
Testing the Setup
7. Sample Server Applications Using IPv6
8. Conclusion
1. Introduction:-
IPv6 is the next-generation protocol designed by the Internet Engineering Task Force (IETF) to replace IPv4, the current version of the Internet Protocol. IPv4 has been remarkably resilient. However, I am not taking into consideration several issues of importance today, such as a large address space, mobility, security, auto configuration and quality of service. To address these concerns, IETF has developed a suite of protocols and standards known as IPv6, which incorporates many of the concepts and proposed methods for updating IPv4. As a result, IPv6 fixes a number of problems in IPv4 and adds many improvements and features that cater to the future mobile Internet.
IPv6 is expected to replace IPv4 gradually, with the two coexisting for a number of years in a transition period. Servers will be dual stack, supporting both IPv4 and IPv6.
In this article, author let me to look closely at IPv6 name resolution and provide a technical tutorial to help readers set up their own IPv6 Linux DNS servers to allow IPv6 name resolution using the latest version of BIND 9.x.
2. General Network Overview:-
Figure – 1.
The following nodes are represented in this architecture:
- Routing server (pc1) acts as an IPv6 software router server and provides router advertisement for all IPv6 nodes.
- DNS IPv6 server (pc2) provides IPv6 name resolution.
- Two application servers, one provides video streaming (pc3) and the other is an Apache-based Web server (pc4).
- Client machines (pc5–7) used for testing purposes.
3. BIND Extensions:-
Maintenance of address information in the DNS is one of several obstacles which have prevented site and provider renumbering from being feasible in IP version 4. To support the storage of IPv6 addresses without impeding renumbering we define the following extensions.
- A new resource record type, “A6”, is defined to map a domain name to an IPv6 address, with a provision for indirection for leading "prefix" bits.
- Existing queries that perform additional section processing to locate IPv4 addresses are redefined to do that processing for both IPv4 and IPv6 addresses.
- A new resource record type, “AAAA” is defined to the Internet class that stores a single IPv6 address
The latest version of BIND is available from the Internet Software Consortium Web site (www.isc.org/products/BIND/). BIND version 9 is a major rewrite of nearly all aspects of the underlying BIND architecture. Many important features and enhancements were introduced in version 9; the most relevant to this article is the support for IPv6. BIND 9.x allows the DNS server to answer DNS queries on IPv6 sockets, provides support for IPv6 resource records (A6, DNAME and so on) and supports bitstring labels. In addition, BIND 9.x makes available an experimental IPv6 resolver library. Many other features are available, and you can read more about them from the BIND Web site.
4. Supporting IPv6 in the Kernel and in Network Binaries:-
An essential step prior to installing the IPv6-compliant BIND version is to enable IPv6 support in the kernel and for the networking binaries on the system supporting IPv6. We have covered this topic in a previous article, “Supporting IPv6 on a Linux Server Node”, in the August 2002 issue of LJ (www.linuxjournal.com/article/4763). After following the tutorial presented in that article, you should be ready to install the latest BIND version with IPv6 support.
5. IP6 Name Resolution:-
Domain names are a meaningful and easy-to-remember “handle” for Internet addresses. The domain name system (DNS) is the way that Internet domain names are located and translated into Internet protocol addresses. Because maintaining a central list of domain name/IP address correspondences is not practical, the lists of domain names and IP addresses are distributed throughout the Internet in a hierarchy of authority. Typically, a DNS server is within close geographic range of your access provider; this DNS server maps the domain names in DNS requests or forwards them to other servers on the Internet. For IPv6 DNS requests, both A6 and AAAA syntax are used to express IPv6 addresses.
AAAA resource record (called quad A record) is formatted as fixed-length data. With AAAA, we can define DNS records for IPv6 name resolution as follows, the same method as A records in IPv4:
$ORIGIN X.EXAMPLE.
N AAAA 2345:00C1:CA11:0001:1234:5678:9ABC:DEF0
N AAAA 2345:00D2:DA11:0001:1234:5678:9ABC:DEF0
N AAAA 2345:000E:EB22:0001:1234:5678:9ABC:DEF0
An A6 resource record is formatted as variable-length data. With A6, it is possible to define an IPv6 address by using multiple DNS records. Here is an example taken from RFC 2874:
$ORIGIN X.EXAMPLE.
N A6 64 ::1234:5678:9ABC:DEF0 SUBNET-1.IP6
SUBNET-1.IP6 A6 48 0:0:0:1:: IP6
IP6 A6 48 0::0 SUBSCRIBER-X.IP6.A.NET.
IP6 A6 48 0::0 SUBSCRIBER-X.IP6.B.NET.
SUBSCRIBER-X.IP6.A.NET. A6 40 0:0:0011:: A.NET.IP6.C.NET.
SUBSCRIBER-X.IP6.A.NET. A6 40 0:0:0011:: A.NET.IP6.D.NET.
SUBSCRIBER-X.IP6.B.NET. A6 40 0:0:0022:: B-NET.IP6.E.NET.
A.NET.IP6.C.NET. A6 28 0:0001:CA00:: C.NET.ALPHA-TLA.ORG.
A.NET.IP6.D.NET. A6 28 0:0002:DA00:: D.NET.ALPHA-TLA.ORG.
B-NET.IP6.E.NET. A6 32 0:0:EB00:: E.NET.ALPHA-TLA.ORG.
C.NET.ALPHA-TLA.ORG. A6 0 2345:00C0::
D.NET.ALPHA-TLA.ORG. A6 0 2345:00D0::
E.NET.ALPHA-TLA.ORG. A6 0 2345:000E::
If we translate the above code into AAAA records, it looks like:
$ORIGIN X.EXAMPLE.
N AAAA 2345:00C1:CA11:0001:1234:5678:9ABC:DEF0
N AAAA 2345:00D2:DA11:0001:1234:5678:9ABC:DEF0
N AAAA 2345:000E:EB22:0001:1234:5678:9ABC:DEF0
Once IPv6 name resolution is configured, we can add domain name system (DNSSEC) to our DNS server. DNSSEC provides three distinct services: key distribution, data origin authentication and transaction and request authentication.
6. Configuring IPv6 DNS and DNSSEC:-
- Types of zones:-
DNS queries can be resolved in many different ways. For instance, a DNS server can use its cache to answer a query or contact other DNS servers on behalf of the client to resolve the name fully. When the DNS server receives a query, it first checks to see if it can answer it authoritatively, based on the resource record information contained in a locally configured zone on the server. If the queried name matches a corresponding resource record in the local zone information, the server answers authoritatively, using this information to resolve the queried name. For a complete DNS query process, there are four existing DNS zones:
- Master: - Stores original and authoritative zone records for a namespace, and answers queries about the namespace from other nameservers.
- Slave: - Answers queries from other nameservers concerning namespaces for which it is considered an authority. However, slave nameservers get their namespace information from master nameservers.
- Stub: - A stub zone is much like a slave zone and behaves similarly, but it replicates only the NS records of a master zone rather than the whole zone. Stub zones keep track of which DNS servers are authoritative for the organization. They directly contact the root DNS server to determine which servers are authoritative for which domain.
- forwarding: - Forwards requests to a specific list of nameservers for name resolution. If none of the specified nameservers can perform the resolution, the resolution fails.
- Main Configuration file:-
To map this to our network (Figure 1), we need to create a master server for our own domain, secv6.your.domain. provides a sample /etc/named.conf configuration. (The secret key is truncated to fit on a line.)
/etc/named.conf
options {
directory "/var/named";
};
// a caching only nameserver config
zone "." IN {
type hint;
file "named.ca";
};
// this defines the loopback name lookup
zone "localhost" IN {
type master;
file "master/localhost.zone";
allow-update { none; };
};
// this defines the loopback reverse name lookup
zone "0.0.127.in-addr.arpa" IN {
type master;
file "master/localhost.rev";
allow-update { none; };
};
// This defines the secv6 domain name lookup
// Secure (signed) zone file is
// secv6.your.domain.signed
// Regular zone file is secv6.your.domain
zone "secv6.your.domain" IN {
type master;
file "master/secv6.your.domain.signed";
// file "master/secv6.your.domain";
};
// this defines the secv6 domain reverse
// name lookup (AAAA)
zone "secv6.int" IN {
type master;
file "master/secv6.int";
};
// this defines the secv6 domain reverse
// name lookup (A6)
zone "secv6.arpa" IN {
type master;
file "master/secv6.rev";
};
// secret key truncated to fit
key "key" {
algorithm hmac-md5;
secret "HxbmAnSO0quVxcxBDjmAmjrmhgDUVFcFNcfmHC";
};
- Configuration file for domain:-
The next file to edit is /var/named/master/secv6.your.domain. Our example uses both AAAA and A6 formats. The $INCLUDE directive at the end includes the public portion of the zone key. Keep the private portion of the key private. The private key has private appended at the end, whereas key postfixes the public key. If you have any concerns regarding DNSSEC keys and their permissions, consult the BIND manual. Below, we display a typical IPv6 DNS domain configuration for secv6.your.domain.
/var/named/master/secv6.your.domain
$TTL 86400
$ORIGIN secv6.your.domain.
@ IN SOA secv6.your.domain. hostmaster.your.domain. (
2002011442 ; Serial number (yyyymmdd-num)
3H ; Refresh
15M ; Retry
1W ; Expire
1D ) ; Minimum
IN MX 10 noah.your.domain.
IN NS ns.secv6.your.domain.
$ORIGIN secv6.your.domain.
ns 1D IN AAAA fec0::1:250:b7ff:fe14:35d0
1D IN A6 0 fec0::1:250:b7ff:fe14:35d0
secv6.your.domain. 1D IN AAAA fec0::1:250:b7ff:fe14:35d0 1D IN A6 0 \
fec0::1:250:b7ff:fe14:35d0
pc2 1D IN AAAA fec0::1:250:b7ff:fe14:35d0 1D IN A6 0 \
fec0::1:250:b7ff:fe14:35d0
pc3 1D IN A6 0 fec0::1:250:b9ff:fe00:131 1D IN AAAA \
fec0::1:250:b9ff:fe00:131
pc6 1D IN A6 0 fec0::1:250:b7ff:fe14:3617 1D IN AAAA \
fec0::1:250:b7ff:fe14:3617
pc4 1D IN A6 0 fec0::1:250:b7ff:fe14:35c4 1D IN AAAA \
fec0::1:250:b7ff:fe14:35c4
pc5 1D IN A6 0 fec0::1:250:b7ff:fe14:361b 1D IN AAAA \
fec0::1:250:b7ff:fe14:361b
pc7 1D IN A6 0 fec0::1:250:b7ff:fe14:365a 1D IN AAAA \
fec0::1:250:b7ff:fe14:365a
pc1 1D IN A6 0 fec0::1:250:b9ff:fe00:12e 1D IN AAAA \
fec0::1:250:b9ff:fe00:12e
pc1 1D IN A6 0 fec0:0:0:1::1 1D IN AAAA \ fec0:0:0:1::1
$INCLUDE "/var/named/master/Ksecv6.your.domain.+003+27034.key"
Now, I will show how to generate a zone key. The working directory for this step is important because the keys are placed there. It is suggested to place the keys in /var/named/master. The following command generates a 768-bit DSA key for the zone:
% dnssec-keygen -a DSA -b 768 -n ZONE secv6.your.domain
By default, all zone keys that have an available private key are used to generate signatures. The keys must be either in the working directory or included in the zone file. The following command signs the secv6.your.domain zone, assuming it is in a file called /var/named/master/secv6.your.domain:
% dnssec-signzone -o secv6.your.domain secv6.your.domain
One output file is produced: /var/named/master/secv6.your.domain.signed. This file should be referenced by /etc/named.conf as the input file for the zone.
The remaining configuration files are localhost.zone , localhost.rev , secv6.rev and secv6.int . The difference between reverse lookup zone files secv6.rev and secv6.int is that one can be specified using A6 strings (that do not need to be reversed in secv6.rev) and the other with reverse AAAA format addresses in secv6.int. For instance, ping6 can refer only to secv6.int domain because it does not support A6 format.
/var/named/master/localhost.zone
// localhost.zone Allows for local communications
// using the loopback interface
$TTL 86400
$ORIGIN localhost.
@ 1D IN SOA @ root (
42 ; serial (d. adams)
3H ; refresh
15M ; retry
1W ; expire
1D ) ; minimum
1D IN NS @
1D IN A 127.0.0.1
/var/named/master/localhost.rev
// localhost.rev Defines reverse DNS lookup on
// loopback interface
$TTL 86400
$ORIGIN 0.0.127.in-addr.arpa.
@ IN SOA 0.0.127.in-addr.arpa. hostmaster.secv6.your.domain. (
42 ; Serial number (d. adams)
3H ; Refresh
15M ; Retry
1W ; Expire
1D ) ; Minimum
NS ns.secv6.your.domain.
MX 10 noah.ip6.your.domain.
PTR localhost.
/var/named/master/secv6.rev
// secv6.rev Defines reverse lookup for secv6
// domain in A6 format
$TTL 86400
$ORIGIN secv6.arpa.
@ IN SOA secv6.arpa. hostmaster.secv6.your.domain. (
2002011442 ; Serial number (yyyymmdd-num)
3H ; Refresh
15M ; Retry
1W ; Expire
1D ) ; Minimum
NS ns.secv6.your.domain.
MX 10 noah.your.domain.
; fec0:0:0:1::/64
$ORIGIN \[xfec0000000000001/64].secv6.arpa.
\[x0250b7fffe1435d0/64] 1D IN PTR pc2.secv6.your.domain.
\[x0250b9fffe000131/64] 1D IN PTR pc3.secv6.your.domain.
\[x0250b7fffe143617/64] 1D IN PTR pc6.secv6.your.domain.
\[x0250b7fffe1435c4/64] 1D IN PTR pc4.secv6.your.domain.
\[x0250b7fffe14361b/64] 1D IN PTR pc5.secv6.your.domain.
\[x0250b7fffe14365a/64] 1D IN PTR pc7.secv6.your.domain.
\[x0250b9fffe00012e/64] 1D IN PTR pc1.secv6.your.domain.
/var/named/master/secv6.int
// secv6.int Defines reverse lookup for secv6
// domain in AAA format
$TTL 86400
$ORIGIN secv6.int.
@ IN SOA secv6.int. hostmaster.secv6.your.domain. (
2002011442 ; Serial number (yyyymmdd-num)
3H ; Refresh
15M ; Retry
1W ; Expire
1D ) ; Minimum
NS ns.secv6.your.domain.
MX 10 noah.your.domain.
; fec0:0:0:1::/64
$ORIGIN 1.0.0.0.0.0.0.0.0.0.0.0.0.c.e.f.secv6.int.
0.d.5.3.4.1.e.f.f.f.7.b.0.5.2.0 IN PTR pc2.secv6.your.domain.
e.2.1.0.0.0.e.f.f.f.9.b.0.5.2.0 IN PTR pc1.secv6.your.domain.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 IN PTR pc1.secv6.your.domain.
1.3.1.0.0.0.e.f.f.f.9.b.0.5.2.0 IN PTR pc3.secv6.your.domain.
7.1.6.3.4.1.e.f.f.f.7.b.0.5.2.0 IN PTR pc6.secv6.your.domain.
4.c.5.3.4.1.e.f.f.f.7.b.0.5.2.0 IN PTR pc4.secv6.your.domain.
b.1.6.3.4.1.e.f.f.f.7.b.0.5.2.0 IN PTR pc5.secv6.your.domain.
- Starting DNS Daemon :-
Once the installation and configuration steps are complete, you are ready to start the DNS daemon on pc2. Named uses /etc/named.conf by default, although you can specify a different configuration file with the -c option if you want. Depending on where you installed the daemon, enter:
pc2% /usr/local/sbin/named
One additional configuration step is needed on the machines within the IPv6 network: update /etc/resolv.conf to contain the DNS server's IP address. It is important that the IP address is included and not the hostname of the DNS server, because this file is where the system looks to find the address of the DNS. In other words, if you specified the hostname of the DNS server here, how would the system know what IP address corresponds to the DNS' hostname?
/etc/resolv.conf on Client Machines
# To enable secv6 domain, start named on pc2
# and use this file as /etc/resolv.conf
search secv6.your.domain
nameserver fec0::1:250:b7ff:fe14:35d0
Testing the Setup:-
We use two simple methods of testing the setup. The first verifies that A6 addresses are enabled in the DNS server, and the second verifies that AAAA addresses are supported by the DNS server. The tests were performed on pc2. We present only the meaningful output here; otherwise the listing would be too long. For the first example, we use the DNS lookup utility dig to perform a lookup on secv6 domain in A6 format. We then perform a lookup in AAAA format. In both cases, we are not specifying an address to look up, thus our use of 0.0.0.0.
A6 DNS Query
pc2% dig 0.0.0.0 secv6.your.domain a6
; <<>> DiG 9.1.0 <<>> 0.0.0.0 secv6.your.domain A6
[...]
;secv6.your.domain. IN A6
;; ANSWER SECTION:
secv6.your.domain. 86400 IN A6 0 fec0::1:250:b7ff:fe14:35d0
;; AUTHORITY SECTION:
secv6.your.domain. 86400 IN NS ns.secv6.your.domain.
;; ADDITIONAL SECTION:
ns.secv6.your.domain. 86400 IN A6 0 fec0::1:250:b7ff:fe14:35d0
ns.secv6.your.domain. 86400 IN AAAA fec0::1:250:b7ff:fe14:35d0
AAAA DNS Query
pc2% dig 0.0.0.0 secv6.your.domain aaaa
; <<>> DiG 9.1.0 <<>> 0.0.0.0 secv6.your.domain AAAA
[...]
;secv6.your.domain. IN AAAA
;; ANSWER SECTION:
secv6.your.domain. 86400 IN AAAA fec0::1:250:b7ff:fe14:35d0
;; AUTHORITY SECTION:
secv6.your.domain. 86400 IN NS ns.secv6.your.domain.
;; ADDITIONAL SECTION:
ns.secv6.your.domain. 86400 IN A6 0 fec0::1:250:b7ff:fe14:35d0
ns.secv6.your.domain. 86400 IN AAAA fec0::1:250:b7ff:fe14:35d0
For our second test, we include samples of an SSH session connection, first using an IPv6 address and then using an IPv6 hostname.
7. Sample Server Applications Using IPv6:-
In our IPv6 network, we presented two application servers: Apache as a Web server and VideoLan for video streaming. To test IPv6 name resolution when streaming a video, a user on client node pc5 accesses the video-streaming server on pc3. The video server is on pc3 (fec0::1:250:b7ff:fe14:5768), and the video client is on pc5 (fec0::1:250:b7ff:fe50:7c). Sniffing the network communications on pc5 with tcpdump, we captured packets from the video stream. Here is a portion of the trace:
% tcpdump ip6 # only trace IPv6 traffic, must be run as root or setuid root
[snip...]
02:09:26.716040 fec0::1:250:b7ff:fe14:5768.32769 > fec0::1:250:b7ff:fe50:7c.1234:\ udp 1316
02:09:26.735805 fec0::1:250:b7ff:fe14:5768.32769 > fec0::1:250:b7ff:fe50:7c.1234:\ udp 1316
02:09:26.735971 fec0::1:250:b7ff:fe14:5768.32769 > fec0::1:250:b7ff:fe50:7c.1234:\ udp 1316
02:09:26.736082 fec0::1:250:b7ff:fe14:5768.32769 > fec0::1:250:b7ff:fe50:7c.1234:\ udp 1316
02:09:26.755810 fec0::1:250:b7ff:fe14:5768.32769 > fec0::1:250:b7ff:fe50:7c.1234:\ udp 1316
02:09:26.755935 fec0::1:250:b7ff:fe14:5768.32769 > fec0::1:250:b7ff:fe50:7c.1234:\ udp 1316
02:09:26.775787 fec0::1:250:b7ff:fe14:5768.32769 > fec0::1:250:b7ff:fe50:7c.1234:\ udp 1316
The video is displayed properly using X11 output on a Linux X server;
8. Conclusion:-
IPv6 is becoming a reality. For the next few years, we will need to be able to support both IPv4 and IPv6 on our servers before the complete transition to IPv6 occurs. We need different pieces of the puzzle to achieve a full migration to IPv6, and one essential piece is an IPv6-compliant BIND implementation.