def genError(rcode, data):
#-------------------------------------------------------------------------------
## generate header
packet = pbf.BitField(12)
packet[:2] = data[:2]
packet[2] = 0x81
packet[3] = 0x80 | rcode
return packet
def genCNAME(name):
#-------------------------------------------------------------------------------
msg = pbf.BitField([])
for lbl in name.split('.'):
msg.append(len(lbl)) ## set length of this label
msg.extend(bytes(lbl)) ## add the label
msg.append(0) ## add the zero length root label
return msg
def main(argv):
#-------------------------------------------------------------------------------
args, opts = oss.gopt(argv[1:], [], [])
#
# set up database creating reverse mappings and some aliases
#
db = dict(DNS_DATABASE)
for name, addr in DNS_DATABASE.items():
a, b, c, d = addr.split('.')
db[d + '.' + c + '.' + b + '.' + a + '.in-addr.arpa.'] = (name +
'.work.', 1)
db[name + '.work.'] = (addr, 0)
db['m' + d + '.work.'] = (addr, 0)
db['h' + d + '.work.'] = (addr, 0)
pprint.pprint(db)
print()
## start server
udps = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
udps.bind(('', 53))
try:
while 1:
data, addr = udps.recvfrom(1024)
data = pbf.BitField(data)
opcode, query = getQuery(data)
query = unicode(query)
print('---\nQuery: ', opcode, '-> "%s"' % query)
if opcode != 0:
udps.sendto(genError(4, data), addr)
continue
if query in db:
ip_name, ptr = db[query]
resp = genResponse(ip_name, ptr, data)
udps.sendto(resp, addr)
print('Response: %s -> %s' % (query, ip_name))
else:
err, aa, addrs, aliases = dns.sendDNSQuery(
query[:-1], '192.168.1.1')
if err == 0:
resp = genResponse(addrs[0], 0, data)
udps.sendto(resp, addr)
print('Response: %s -> %s' % (query, addrs[0]))
else:
udps.sendto(genError(3, data), addr)
except KeyboardInterrupt:
udps.close()
oss.exit(0)
def genResponse(ip_name, ptrRec, data):
#-------------------------------------------------------------------------------
packet = pbf.BitField(12)
aRec = not ptrRec
## generate header
packet[:2] = data[:2]
packet[2] = 0x84
packet[3] = 0x80
packet.setM(4, 2, 1)
packet.setM(6, 2, 1)
## copy original question
packet.extend(data[12:])
## create answer
packet.append(0xc0) # use pointer
packet.append(0x0c) # to domain name in question
packet.append(0) # root
if aRec:
packet.append(1) # response type - A record
else:
packet.append(12) # response type - PTR record
packet.addM(2, 1) # class (IN)
packet.addM(4, 0xa5a5a5a5) # ttl
if aRec:
packet.addM(2, 4) # rdata_length
packet.extend([int(x) for x in ip_name.split('.')])
else:
name = dns.genCNAME(ip_name)
packet.addM(2, len(name)) # rdata_length
packet.extend(dns.genCNAME(ip_name))
return packet
def sendDNSQuery(name, nameServerIPAddr, dump=False):
#-------------------------------------------------------------------------------
id = random.randint(0, 2**16 - 1)
msg = pbf.BitField(12)
msg.setM(0, 2, id) ## set the id
msg.setBit(2, 0, 1) ## set recursion request
msg.setM(4, 2, 1) ## set query count to 1
for lbl in name.split('.'):
msg.append(len(lbl)) ## set length of this label
msg.extend(bytes(lbl)) ## add the label
msg.append(0) ## add the zero length root label
msg.addM(2, 1) ## set qtype
msg.addM(2, 1) ## set qclass
if dump:
print('Sent packet:')
msg.hexDump()
print()
## send packet
udps = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
udps.sendto(msg, (nameServerIPAddr, 53))
## get packet
data = pbf.BitField(udps.recv(1024))
## ensure it is the correct request
if id == data.getM(0, 2):
if dump:
print('Recved packet:')
pbf.hexDump(data)
print()
#print('QR:', data.getBit(2, 7))
AA = data.getBit(2, 2)
#print('AA:', data.getBit(2, 2))
#print('RD:', data.getBit(2, 0))
#print('RA:', data.getBit(3, 7))
#print('Opcode:', data.getBits(3, 3, 6))
rcode = data.getBits(3, 0, 3)
#print('RCODE:', rcode)
if dump:
print('Q records:', data.getM(4, 2))
print('A records:', data.getM(6, 2))
print('NS records:', data.getM(8, 2))
print('Additional records:', data.getM(10, 2))
if rcode != 0:
return rcode, 0, [], []
## get question records
for i in range(data.getM(4, 2)):
idx, name = getCNAME(12, data)
idx += 5
## get answers
idx, ipaddrs, aliases = getAnswerRecords(idx, data)
if dump:
print()
pbf.hexDump(data[idx:])
print()
for i in range(data.getM(8, 2)):
idx, name = getCNAME(idx, data)
print('NS:', name)
print()
pbf.hexDump(data[idx:])
print()
return 0, AA, ipaddrs, aliases