pingdns

dns-over-ping(8)

You've heard of DNS-over-HTTP, DNS-over-TLS, DNS-over-GRPC... Now get ready for DNS-over-ping(8)!

Resolve names straight from the standard inetutils/iptools ping tool:

$ ping localhost -4 -p "$(printf "cloudflare.com?" | xxd -p -c0)" -c1
PATTERN: 0x636c6f7564666c6172652e636f6d3f
PING  (127.0.0.1) 56(84) bytes of data.
72 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=1667863702756 ms
wrong data byte #16 should be 0x6c but was 0x68
#16	68 10 85 e5 68 10 84 e5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
#48	0 0 0 0 0 0 0 0

---  ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 1667863702755.909/1667863702755.909/1667863702755.909/0.000 ms

Simply read your answer off from the wrong data hexdump:

   68 10 85 e5          68 10 84 e5
=> 0x68.0x10.0x85.0xe5  0x68.0x10.0x84.0xe5 
=  104.16.133.229       104.16.132.229

Limitations

• Only A lookups supported, sorry.

  • Including both IPv4 and IPv6 addresses would necessitate a more complicated output format to avoid ambiguity.
  • The choice is then between IPv4 and IPv6 - IPv4 wins because we can display more IPs (ping will only show data 56 bytes in its errors).

• Names can be at most 15 bytes long.

  • This is because ping only lets you specify 16 byte data patterns - everything beyond 16 bytes is ignored - and a byte more is required for the delimiter (question mark)

• At most 14 IPs can be returned

  • ping will always display 56 bytes of hexdumped wrong data, regardless of how much is in the response packet
  • but, in fairness, I'd be surprised if any names resolve to more than 14 IPs

None of these are inherent limitations of ICMP, rather they are limitations of the ping tool and its output. DNS-over-ICMP could actually be made to work pretty well (but would be less fun).

Running

Optionally, prevent your machine sending its own ICMP responses to incoming ICMP echo requests:

# echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all

Then:

$ go build ./cmd/pingdns
$ sudo setcap cap_net_raw+ep pingdns
$ ./pingdns

Then, in another shell, for example:

$ ping localhost -4 -p "$(printf "jameswillia.ms?" | xxd -p -c0)" -c1