Module 3 Lesson 1 : DNS operation with IPv6

Lesson 1 DNS operation with IPv6

Lesson outline

Ø IPv6 and DNS

Ø Cisco IOS IPv6 DNS client Support

Ø Examples of the DNS Queries

Ø Cisco IOS IPv6 DNS configuration

Ø IPv6 and DDNS

1 IPv6 and DNS

items	IPv4	IPv6	Remark
Hostname to IP address	A record: A 192.168.30.20	AAAA record: AAAA 3FFFE:B00:C18:1::2
IP address to hostname	PTR record: 20.30.168.192.in-addr.arpa.PTR	PTR record: 2.0.0.0.0.0.0.0.0.0.0.0..0.0.0.1.0.0.0.8.1.c.0.0.0.b.0.e.f.f.3.ip6.int  PTR
IP address to hostname		PTR record: $ORIGIN\.......IN PTR

 

DNS for IPv4 does not support IPv6 addresses, new records are defined to support IPv6 addresses.

The following records and new functions are defined:

AAAA records : this is the IPv6 equivalent of the record which implements the hostname to IP address mapping, with AAAA records, the IP address is the IPv6 one

Inverse mapping (IP addressàhostname) use the PTR record as usual, the top-level domain for the IPv6 addresses is :ip6.arpa. at the beginning of IPv6 DNS, the top-level domain was ip6.intàthat mechanism is now deprecated.

The example shows the IPv4 and IPv6 formats of the DNS records.

AAAA records are available since the 4.9.4 release of the ISC Bind software. Note:  PTR means pointer.

 

2    Cisco IOS IPv6 DNS client Support

Cisco IOS has IPv6 DNS client support

Queries DNS server for IPv6/IPv4

Ø First tries queries for an IPv6 address (AAAA record)

Ø If no IPv6 address exists. Then query for an IPv4 address (A record)

Ø When both IPv6 and IPv4 records exit, the IPv6 address is picked first

Ø Static hostname to IPv6 address can also be configured.

Note:

Cisco IOS supports a DNS resolver that supports IPv6 for DNS records and DNS transport on IPv6.

The behavior of the DNS resolution is such that IPv6 addresses will be chosen over IPv4 address. When resolving a hostname to an IP address, the router first queries for an AAAA record. If more than one name server is configured on the router, all servers are queried for the AAAA record. If the DNS response is such that no IPv6 address (AAAA record) is found, the router will send a new query for an A record (IPv4).

3    Examples of the DNS Queries

Router A-------------------------------------------DNS Server

Query = Type=AAAAà

Resp=3ffe:b00:ffff:1::1 Type=AAAA

                           OR

<--Nonexistent

Query= Type =Aà

<--Resp=192.168.30.1 Type =A

DNS resolver verifies for IPv6 AAAA records first

Note:

In this example, router A is configured to use the DNS Server B, Router A queries DNS server B for the AAAA record for the hostname . if DNS server B returns an answer for the AAAA query, the resolution is done, if there is no AAAA record for the query, the router will send a new query asking for the A record of .

The DNS queries between the Router A and DNS Server B, is done using IPv6 transport if the DNS server is identified with its IPv6 address in the router configuration.

 

4    Cisco IOS IPv6 DNS configuration

DNS commands for IPv6:

Ø Define static name for IPv6 address

Ipv6 host []

Example:ipv6 host router1 3ffe:b00:ffff:b::1

Ø Configuring DNS servers to query

ip name-server

example: ip name-server 3ffe:b00:ffff:1::10

Note:

It is possible to define static name for IPv6 addresses using the command ipv6 host . Up to 4 IPv6 addresses can be defined for one hostname.  The “port” field is the default telnet for the associated host.

To specify the DNS server used by the router, use the ip name-server

command. The

can be an IPv4 or IPv6 address. Several DNS servers can be specified with this command – up to 6.

 

5    IPv6 and DDNS

a.   Dynamic DNS (DDNS) provide the capability for secure, authenticated updates of DNS zone files

b.   Updating agent is typically DDNS-aware DHCP server

c.   Profusion of globally routable client systems (IPv6) will lead to greater emphasis on reachability by name for nodes with routable but not static addresses – DDNS function

d.   Not yet widely deployed

 

6    Summary

In this lesson ,you learned to :

Ø Describe the IPv6 DNS records and how DNS works in IPv6

Ø Describe DNS operation with IPv6 AAAA records

Ø Configure and Use DNS on Cisco equipment