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THE IPv6 AAAA RECORD:

INTRODUCTION:

INTERNET PROTOCOL VERSION 6 (IPV6):

IPv6 is a version of the Internet Protocol (IP) that is designed to succeed Internet Protocol version 4 (IPv4). The Internet operates by transferring data in small packets that are independently routed across networks as specified by an international communications protocol known as the Internet Protocol. Each data packet contains two numeric addresses that are the packet's origin and destination devices. Since 1981, IPv4 has been the publicly used version of the Internet Protocol, and it is currently the foundation for most Internet communications. The Internet's growth has created a need for more addresses than IPv4 is capable of. IPv6 allows for vastly more numerical addresses, but switching from IPv4 to IPv6 may be a difficult process.       

 DNS FOR IPv6:

IPv6 supports DNS record types that are supported in the DNS name-to-address and address-to-name lookup processes. The DNS record types support IPv6 addresses. IPv6 also supports the reverse mapping of IPv6 addresses to DNS names.

A name server is used to track information associated with domain names. A name server can maintain a database of hostname-to-address mappings. Each name can map to one or more IPv4 addresses, IPv6 addresses, or both address types. In order to use this service to map domain names to IPv6 addresses, you must specify a name server and enable the DNS.

The Cisco IOS software maintains a cache of hostname-to-address mappings for use by the connect, telnet, and ping commands, related Telnet support operations, and many other commands that generate command output. This cache speeds the conversion of names to addresses.

Similar to IPv4, IPv6 uses a naming scheme that allows a network device to be identified by its location within a hierarchical name space that provides for domains. Domain names are joined with periods (.) as the delimiting characters. For example, Cisco is a commercial organization that is identified by a com domain name, so its domain name is cisco.com. A specific device in this domain, the FTP server, for example, is identified as ftp.cisco.com.

IPv6 DNS RECORD TYPES:

  • AAAA RECORD TYPES: Maps a hostname to an IPv6 address. (Equivalent to an A record in IPv4.)
     Note Support for AAAA records and A records over an IPv6 transport or IPv4 transport is in Cisco IOS
     Release 12.2(8)T or later releases.

  • PTR RECORD TYPES: Maps a hostname to an IPv6 address. (Equivalent to an A record in IPv4.)
Note Support for AAAA records and A records over an IPv6 transport or IPv4 transport is in Cisco IOS Release 12.2(8)T or later releases.

IPV6 AAAA RECORD:

A’s record and the AAAA record play an important part during the DNS resolution process. The main difference between them is that an A record is responsible for translating a hostname to its corresponding IPv4 address, while the AAAA RECORD is working for specifying the IPv6 address for a certain host.

When we start deploying IPv6 services for outside users, you will need to add AAAA record for those hosts in your DNS and set up proper delegation for IPv6.arpa to handle PTR records. Before you do this, it is a good idea to make sure that you have reasonable IPv6 connectivity so that IPv6 users won't be diverted to high-latency indirect paths when they start using the AAAA records.

Also, to help users on your network, set up the IPv6 services described in First Steps for ISPs. It wouldn't hurt to do an audit of customers who are using other tunnel broker servers and contact them, pointing out that you have a local tunnel broker service. If you don't do this, it is likely that the new AAAA records for your service will cause some of your users to experience much higher latency because they get their IPv6 packets from a distant tunnel broker. It will appear that your network is suffering from strange latency problems since the server with the AAAA record is on your network.

A’s record is understandably much more used than the AAAA record, since IPv4 is currently the dominant Internet Protocol version. However, it holds a great potential, given the future possibility for IPv6 to become the new IP address system.                                                                                                                                          

IPV6 IN THE DOMAIN NAME SYSTEM(DNS):

In the Domain Name System, hostnames are mapped to IPv6 addresses by AAAA resource records, so-called quad-A records. For reverse resolution, the IETF reserved the domain ip6.arpa, where the name space is hierarchically divided by the 1-digit hexadecimal representation of nibble units (4 bits) of the IPv6 address. This scheme is defined in RFC 3596.

A new type of resource record is defined for IPv6—the AAAA record. This record provides name-to-IPv6 address mapping. A DNS resolver on an IPv6/IPv4 node must be able to handle both IPv4 A resource records and IPv6 AAAA resource records. When a node queries the DNS server for an address, an A record or an AAAA record is returned. The type of address returned determines the protocol that is used. If an A record is returned, the node uses its IPv4 address and the IPv4 protocol for communication with the requested destination. If an AAAA address is returned, IPv6 is used.

When an IPv4-compatible address is assigned to an IPv6/IPv4 host, both an AAAA record and an A record are defined in the DNS. The AAAA record lists the full 128-bit IPv6 address, and the A record lists the low-order 32 bits of the address. Both types are listed so that IPv6-only nodes can query the server and receive an IPv6 address and IPv4-only nodes can receive the IPv4 address.

Now, if both AAAA and A type records are listed for an IPv4-compatible address, the DNS resolver has some choices on what to return, and what it returns affects which protocol is used in the communication:

  •         Return only the IPv6 address to the application.
  •         Return only the IPv4 address to the application.
  •         Return both addresses to the application.

The address or the order of the addresses returned affects the type of IP traffic generated.

SPECIAL HOSTNAMES:

One way to avoid such issues and allow testing without disrupting production services is to set up special domain names. Initially, you can add a name which only returns an AAAA record. This assures that connectivity is IPv6 and does not require change to the existing host name. (Note: You may have to configure your service to recognize the new name, e.g. add a ServerAlias directive to an Apache virtual host.) To switch to production IPv6 use, add an AAAA record to the primary host name. Adding another name that only returns an A record will provide a way to test with IPv4 only.

Initial testing:
 
           www.your.domain                       (Original name. A record only.)
           www.ipv6.your.domain               (AAAA record only.)
 
Production:
           www.your.domain                       (A and AAAA record.)
           www.ipv6.your.domain               (AAAA record only.)
           www.ipv4.your.domain               (A record only.)
 
Substitute www with whatever hostname you are using. The above form is what is in general use around the internet and what some people will try in cases where a DNS name has both an AAAA and A records and one of them does not work.

REVERSE DNS:

Reverse DNS works via PTR records in your zones. For IPv4, the bits are reversed, such that a PTR record for 192.168.0.0 would look like 0.0.168.192 IN PTR your. Hostname.. The same is true for IPv6, except that you must seperate each character with A’s .

 This means that a PTR record for 2008:64:128::ee:1 would look like

1.0.0.0.e.e.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.2.1.0.4.6.0.0.8.0.0.2 IN PTR your.hostname. or a PTR record for the loopback address of ::1 would look like 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 IN PTR localhost.. Note that zeroes must be expanded, there is no way to replicate a :: in ip6.arpa DNS records.

There are questions about scalability of reverse DNS in IPv6. In IPv4, large ISPs simply prepopulate reverse zones with records for every possible address. In IPv6, that would be impossible. A variety of options are available, including generating queries on the fly, dynamic DNS, and simply not responding.

Note - That this section only discusses the ip6.arpa method of reverse DNS. Formerly, the ip6.int method existed as well, however the IETF has been pushing towards standardization around the ip6.arpa method, which is what is in widest use in modern systems today.

EXAMPLE OF DNS QUERY: IPv6 vs DNS:

                                                IPv4                                                                 IPv6

Hostname to                     A Record:                                                     AAAA Record: 

IP address            www.abc.test. A 192.168.30.1                    www.abc.test AAAA 3FFE:B00:C18:1::2                   
--------------
                                        IPv4 PTR Record                                          IPv6 PTR Record:
                        
IP address to      1.30.168.192.in-addr.arpa. PTR               2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.8.1.c.0.
Host Name                         www.abc.test.                               0.0.b.0.e.f.f.3.ip6.arpa PTR www.abc.test.


IOS IPV6 DNS CLIENT SUPPORT:

  •  IOS supports IPv6 DNS client
  •  Queries DNS servers for Iv6/IPv4:
First tries queries for an IPv6 address (AAAA record)If no IPv6 address exists, then query for an IPv4 address (A record) 
When both IPv6 and IPv4 records exists, the IPv6 address is picked first 
  •  Static hostname to IPv6 address can also be configured
  •  Note: IPv6 stacks on Windows XP, Linux, FreeBSD, etc also
Pick IPv6 address before IPv4 address if both exist


ROUTER A                  -  >          DNS SERVER B

Queerryy==www..eexxaampllee..orrg Tyypee==AAAA

< -

Reessp==33ffffee::b0000::ffffffff::11::::11 Tyypee==AAAA

OR
Non--eexxiisstteentt

                                   -   >
Queerryy==www..eexxaampllee..orrg Tyypee==A

< -

Reessp==119922..116688..3300..11 Tyypee==A


  •  DNS resolver picks IPv6 AAAA record first 


This Article Written Author By: Premakumar Thevathasan. CCNA, CCNP, CCIP, MCSA, MCSE, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+.
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