go-dns dynamically generates AAAA and PTR dns records for an IPv6 prefix. In cases where SLAAC, and other dynamic IPv6 methods are being used to assign addresses, it is not feasible to maintain reverse DNS records for all assignable addresses. go-dns will dynamically return AAAA and PTR records based on the queried IPv6 address.
Given the following IPv6 prefix and address the following reverse address will be generated:
Prefix:
2001:db8:1:1::/64
Address:
2001:db8:1:1:14f5:d526:ec16:ba83 -> 14f5d526ec16ba83.dynamic.ipv6.example.com
where the original network prefix is: 2001:db8:1::/48
The configuration file config.toml is as follows:
[dns]
port = 15353
protocol = "udp"
[dns.domain]
response_type = "NxError"
domain = "ipv6.example.com"
prefix = "2001:db8:1::"
mask = 48
[dns.soa]
ttl = 300
refresh = 3600
retry = 1800
expire = 10800
minimum = 300
mname = "ns-ipv6.example.com"
rname = "dns.example.com"
[dns.ns]
servers = ["ns-ipv6.example.com"]
[subdomain."dynamic.ipv6.example.com"]
response_type = "Dynamic"
prefix = "2001:db8:1:1::"
mask = 64
[static."a.dynamic.ipv6.example.com"]
prefix = "2001:db8:1:1::100"The dns section contains the configurable options for the DNS server. The configuration options are:
| Option | Description | Options |
|---|---|---|
| port | the port the DNS server will listen on | Any value port |
| protocol | the protocol to use | tcp or udp |
The dns.domain section contain the top-level response for this domain prefix. If your network is broken into a set of smaller networks, then this can be an NxError type which will act as a catch all for top-level dns queries and return an NXERROR
| Option | Description |
|---|---|
| prefix | The IPv6 prefix for the reverse lookup |
| comain | The top-level domain being managed |
| response_type | The response type for this subdomain |
| mask | The network mask |
The dns.soa sections contains the defaults for the SOA records for the domain:
| Option | Description | Example |
|---|---|---|
| ttl | The time to live value of the SOA record | 300 |
| refresh | Refresh period for secondary lookups | 3600 |
| retry | The retry period for the secondary lookups | 1800 |
| expire | The number of seconds before before the record expires | 10800 |
| minimum | Time to live | 300 |
| mname | The primary nameserver for this zone | |
| rname | Email address for the administrator for the zone |
The dns.ns sections contains the defaults for the ns records for the domain:
| Option | Description |
|---|---|
| server | The list of namesevers for this domain |
The subdomain section contains the defintions of the prefix and the domain names for the generated responses. Each sub-domain should be contains in a section of the following form [subdomain."<sub.domain.name>"], where each secion has the following form:
| Option | Description |
|---|---|
| prefix | The IPv6 prefix for the reverse lookup |
| response_type | The response type for this subdomain |
| mask | The network mask |
There are currently three types of responses, these are NxError, Dynamic, or Static. These response types determine how the responses are constructed.
The NxError response type will return NXERROR for every query. It can be uses for fall through responses or where you need to return an NXERROR for every query.
The Dynamic response type will return an AAAA and corresponding PTR for a DNS query. The domain name that is returned is of the form:
xxxxxxxxxxxxxxxx.domain.example.com
where the first part of the domain is the hex representation of the IP address after the IPv6 prefix. The domain name is reversable so the IPv6 address can be reconstructed from the DNS name.
Returns an AAAA and PTR record for a specificed DNS name. This will override any dynamic prefix responses that may include a the specified IP address. The mask for a static response will always be defaulted to 128, regardless of any prefix value that has been set.
The example config above will create a valid instance of go-dns, however it will not be useful outside a few examples:
- Query the reverse domain for
2001:db8:1:1::1:
$ dig @127.0.0.1 -p 15353 -x 2001:db8:1:1::1
; <<>> DiG 9.11.5-P1-1ubuntu2.5-Ubuntu <<>> @127.0.0.1 -p 15353 -x 2001:db8:1:1::1
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6047
;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR
;; ANSWER SECTION:
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. 3600 IN PTR 0000000000000001.dynamic.ipv6.example.com.
;; Query time: 0 msec
;; SERVER: 127.0.0.1#15353(127.0.0.1)
;; WHEN: Sun Aug 18 13:37:43 SAST 2019
;; MSG SIZE rcvd: 217- Query the reverse domain for
2001:db8:1:1::100(a static assignment in config)
$ dig @127.0.0.1 -p 15353 -x 2001:db8:1:1::100
; <<>> DiG 9.11.5-P1-1ubuntu2.5-Ubuntu <<>> @127.0.0.1 -p 15353 -x 2001:db8:1:1::100
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12620
;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;0.0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR
;; ANSWER SECTION:
0.0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. 3600 IN PTR a.dynamic.ipv6.example.com.
;; Query time: 0 msec
;; SERVER: 127.0.0.1#15353(127.0.0.1)
;; WHEN: Sun Aug 18 13:38:12 SAST 2019
;; MSG SIZE rcvd: 202- Perform a lookup dyanmic domain:
$ dig @127.0.0.1 -p 15353 AAAA 0000000000000001.dynamic.ipv6.example.com
; <<>> DiG 9.11.5-P1-1ubuntu2.5-Ubuntu <<>> @127.0.0.1 -p 15353 AAAA 0000000000000001.dynamic.ipv6.example.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36486
;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;0000000000000001.dynamic.ipv6.example.com. IN AAAA
;; ANSWER SECTION:
0000000000000001.dynamic.ipv6.example.com. 3600 IN AAAA 2001:db8:1:1::1
;; Query time: 0 msec
;; SERVER: 127.0.0.1#15353(127.0.0.1)
;; WHEN: Sun Aug 18 13:44:25 SAST 2019
;; MSG SIZE rcvd: 128- Perform a lookup for a static domain
$ dig @127.0.0.1 -p 15353 AAAA a.dynamic.ipv6.example.com
; <<>> DiG 9.11.5-P1-1ubuntu2.5-Ubuntu <<>> @127.0.0.1 -p 15353 AAAA a.dynamic.ipv6.example.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50346
;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;a.dynamic.ipv6.example.com. IN AAAA
;; ANSWER SECTION:
a.dynamic.ipv6.example.com. 3600 IN AAAA 2001:db8:1:1::100
;; Query time: 0 msec
;; SERVER: 127.0.0.1#15353(127.0.0.1)
;; WHEN: Sun Aug 18 13:38:46 SAST 2019
;; MSG SIZE rcvd: 98
Running go-dns is as simple as running:
$ ./go-dns -c <config_file>
The server will start listening on the specified port and will start to respond to dns requests.