NSID enumerator: show DNS servers behind anycast IPs using NSID

NOTE: there is a Go implementation in the experimental/ subfolder

As simple as that: run DNS queries towards an anycast-enabled, NSID-enabled DNS server (e.g. the root servers) to know what the backend servers are. Leverage ECMP (Equal-Cost MultiPath) for the enumeration.

This tool uses NSID to get the backend server name, which is in-band in any regular DNS query. See --id-server if you want to also run a CHAOS/TXT id.server. query.

Dependencies

Python 3
dnspython

Example:

Enumeration

Enumerate the backend servers behind k.root-servers.net. using 10 paths:

$ ./nsidenumerator.py k.root-servers.net -e 10
Enumerating 10 paths
Found 3 servers
b'ns1.gb-lon.k.ripe.net'
b'ns2.gb-lon.k.ripe.net'
b'ns3.gb-lon.k.ripe.net'

## Statistics
Total DNS queries      : 10
Timeouts               : 0
Percent failed queries : 0.00

## Warnings
    none

Server ID

You can specify -I/--id-server to also specify an id.server payload, i.e. qtype TXT, qclass CHAOS and qname id.server.. This option is useful if the target does not support NSID but it replies to TXT/CHAOS queries. The tool will show additional information:

$ ./nsidenumerator.py -I -e 10 9.9.9.9 
Warning: using --id-server overrides qname, qclass and qtype
Enumerating 10 paths
Found 0 servers (target not supporting NSID?)
Showing id.server results:
b'res100.ams.rrdns.pch.net'
b'res200.ams.rrdns.pch.net'
b'res300.ams.rrdns.pch.net'

## Statistics
Total DNS queries      : 10
Timeouts               : 0
Percent failed queries : 0.00

## Warnings
    none

Single query

One query (hence one path and one backend server), source port 12345, verbose mode:

$ ./nsidenumerator.py k.root-servers.net -v
DNS query to k.root-servers.net(193.0.14.129). Qname: '.', qtype: A, qclass: IN, sport: 12345, dport: 53, timeout 1.0
Found 1 servers
b'ns2.gb-lon.k.ripe.net'

## Statistics
Total DNS queries      : 1
Timeouts               : 0
Percent failed queries : 0.00

## Warnings
    none

Usage

$ ./nsidenumerator.py --help
usage: nsidenumerator.py [-h] [-n QNAME] [-t QTYPE] [-c {IN,CH}] [-T TIMEOUT]
                         [-s SPORT] [-d DPORT] [-e ENUMERATE] [-I] [-v] [-q]
                         target

positional arguments:
  target                The target DNS server.

optional arguments:
  -h, --help            show this help message and exit
  -n QNAME, --qname QNAME
                        The DNS name to query for. Default: '.'
  -t QTYPE, --qtype QTYPE
                        Query type to use. Default: A
  -c {IN,CH}, --qclass {IN,CH}
                        Query class to use. Default: IN
  -T TIMEOUT, --timeout TIMEOUT
                        Timeout before the DNS request expires
  -s SPORT, --sport SPORT
                        The UDP source port to use for the query. Default:
                        12345
  -d DPORT, --dport DPORT
                        The UDP destination port to use for the query.
                        Default: 53
  -e ENUMERATE, --enumerate ENUMERATE
                        Enumerate DNS servers using the specified number of
                        paths. Default: None
  -I, --id-server       Run a CHAOS TXT id.server. query along with NSID, and
                        match the answers
  -v, --verbose         Print verbose output. Default: False
  -q, --quiet           Print the minimum necessary information. Default:
                        False