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# coding=utf-8
import datetime
import sys
import time
import threading
import traceback
import SocketServer
from dnslib import *
class DomainName(str):
def __getattr__(self, item):
return DomainName(item + '.' + self)
D = DomainName('')
IP = ''
TTL = 60 * 5
PORT = 5053
soa_record = SOA(
mname=D.ns1, # primary name server
rname=D.andrei, # email of the domain administrator
201307231, # serial number
60 * 60 * 1, # refresh
60 * 60 * 3, # retry
60 * 60 * 24, # expire
60 * 60 * 1, # minimum
ns_records = [NS(D.ns1), NS(D.ns2)]
records = {
D: [A(IP), AAAA((0,) * 16), MX(D.mail), soa_record] + ns_records,
D.ns1: [A(IP)], # MX and NS records must never point to a CNAME alias (RFC 2181 section 10.3)
D.ns2: [A(IP)],
D.mail: [A(IP)],
D.andrei: [CNAME(D)],
def dns_response(data):
request = DNSRecord.parse(data)
print request
reply = DNSRecord(DNSHeader(, qr=1, aa=1, ra=1), q=request.q)
qname = request.q.qname
qn = str(qname)
qtype = request.q.qtype
qt = QTYPE[qtype]
if qn == D or qn.endswith('.' + D):
for name, rrs in records.iteritems():
if name == qn:
for rdata in rrs:
rqt = rdata.__class__.__name__
if qt in ['*', rqt]:
reply.add_answer(RR(rname=qname, rtype=QTYPE[rqt], rclass=1, ttl=TTL, rdata=rdata))
for rdata in ns_records:
reply.add_ns(RR(rname=D, rtype=QTYPE.NS, rclass=1, ttl=TTL, rdata=rdata))
reply.add_ns(RR(rname=D, rtype=QTYPE.SOA, rclass=1, ttl=TTL, rdata=soa_record))
print "---- Reply:\n", reply
return reply.pack()
class BaseRequestHandler(SocketServer.BaseRequestHandler):
def get_data(self):
raise NotImplementedError
def send_data(self, data):
raise NotImplementedError
def handle(self):
now = datetime.datetime.utcnow().strftime('%Y-%m-%d %H:%M:%S.%f')
print "\n\n%s request %s (%s %s):" % (self.__class__.__name__[:3], now, self.client_address[0],
data = self.get_data()
print len(data), data.encode('hex') # repr(data).replace('\\x', '')[1:-1]
except Exception:
class TCPRequestHandler(BaseRequestHandler):
def get_data(self):
data = self.request.recv(8192).strip()
sz = int(data[:2].encode('hex'), 16)
if sz < len(data) - 2:
raise Exception("Wrong size of TCP packet")
elif sz > len(data) - 2:
raise Exception("Too big TCP packet")
return data[2:]
def send_data(self, data):
sz = hex(len(data))[2:].zfill(4).decode('hex')
return self.request.sendall(sz + data)
class UDPRequestHandler(BaseRequestHandler):
def get_data(self):
return self.request[0].strip()
def send_data(self, data):
return self.request[1].sendto(data, self.client_address)
if __name__ == '__main__':
print "Starting nameserver..."
servers = [
SocketServer.ThreadingUDPServer(('', PORT), UDPRequestHandler),
SocketServer.ThreadingTCPServer(('', PORT), TCPRequestHandler),
for s in servers:
thread = threading.Thread(target=s.serve_forever) # that thread will start one more thread for each request
thread.daemon = True # exit the server thread when the main thread terminates
print "%s server loop running in thread: %s" % (s.RequestHandlerClass.__name__[:3],
while 1:
except KeyboardInterrupt:
for s in servers:
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error in line 57: if qn == D or qn.endswith('.' + D):

change with: if qn == D or qn.endswith(D + '.'):

Now I got this error:

Traceback (most recent call last):
File "", line 95, in handle
File "", line 71, in dns_response
reply.add_ns(RR(rname=D, rtype=QTYPE.NS, rclass=1, ttl=TTL, rdata=rdata))
AttributeError: 'DNSRecord' object has no attribute 'add_ns'

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This line did not work
reply.add_ns(RR(rname=D, rtype=QTYPE.SOA, rclass=1, ttl=TTL, rdata=soa_record))

So I changed it with the following
reply.add_answer(RR(rname=D, rtype=QTYPE.NS, rclass=1, ttl=TTL, rdata=rdata))

Now the server worked with dig:

$ dig @ -p 5053

; <<>> DiG 9.9.5-3ubuntu0.9-Ubuntu <<>> @ -p 5053
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55402
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;       IN  A

;; ANSWER SECTION:    300 IN  NS    300 IN  NS    300 IN  NS

;; Query time: 2 msec
;; WHEN: Wed Oct 05 17:39:43 CEST 2016
;; MSG SIZE  rcvd: 83

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xrl1 commented Nov 3, 2016

As @Th4nat0s commented, if the first byte of the transaction id represents a whitespace char (which is allowed), than strip removes him, and the DNS query becomes invalid.
It causes DNSRecord.parse function to raise an exception.

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I'm afraid there are quite a few errors with this, however it did alert me to the excellent dnslib library, thanks. If only the author had used it's built in tools rather than trying to roll his/her own - for example dnslib has DNSServer which takes away a lot of the pain.

Here's a complete rewrite, where:

  • actually works (tested a fair bit with dig).
  • works with python 3.6 (and probably 3.5, but not tested), should pretty much pass flake8
  • implements some sensible defaults (for ttl, rname etc.) and does a bit of cleverness (eg. returned TLDR SOA record for missing subdomains).
  • is extensible, you should just need to edit ZONES to add whatever other records you wish.

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SeanFelipe commented Apr 6, 2017

Thanks for the code and comments -- I'm about to use this for a project to help teachers manage what websites students can access, to help reduce distractions in the classroom.

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dugduy commented Apr 10, 2022

thanks man!!!

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