def parse_dhcp_resp(response, debug):
"""
Parse DHCP response:
Returns endpoint server or None on error.
"""
if debug == True:
print('Parsing Dhcp response')
bytes_recv = len(response)
endpoint = None
gateway = None
routes = None
# Walk all the returned options, parsing out what we need, ignoring the
# others. We need the custom option 245 to find the the endpoint we talk to
# options 3 for default gateway and 249 for routes; 255 is end.
i = 0xF0 # offset to first option
while i < bytes_recv:
option = util.str_to_ord(response[i])
length = 0
if (i + 1) < bytes_recv:
length = util.str_to_ord(response[i + 1])
if debug == True:
print("DHCP option {0} at offset:{1} with length:{2}",
hex(option), hex(i), hex(length))
if option == 255:
if debug == True:
print("DHCP packet ended at offset:{0}", hex(i))
break
elif option == 249:
routes = parse_route(response, option, i, length, bytes_recv)
elif option == 3:
gateway = parse_ip_addr(response, option, i, length, bytes_recv)
if debug == True:
print("Default gateway:{0}, at {1}", gateway, hex(i))
elif option == 245:
endpoint = parse_ip_addr(response, option, i, length, bytes_recv)
if debug == True:
print("Azure cloud control endpoint IP:{0}, at {1}", endpoint,
hex(i))
else:
if debug == True:
print("Skipping DHCP option:{0} at {1} with length {2}",
hex(option), hex(i), hex(length))
i += length + 2
return endpoint, gateway, routes
def parse_route(response, option, i, length, bytes_recv):
# http://msdn.microsoft.com/en-us/library/cc227282%28PROT.10%29.aspx
print("Routes at offset: {0} with length:{1}", hex(i), hex(length))
routes = []
if length < 5:
print("Data too small for option:{0}", option)
j = i + 2
while j < (i + length + 2):
mask_len_bits = util.str_to_ord(response[j])
mask_len_bytes = (((mask_len_bits + 7) & ~7) >> 3)
mask = 0xFFFFFFFF & (0xFFFFFFFF << (32 - mask_len_bits))
j += 1
net = util.unpack_big_endian(response, j, mask_len_bytes)
net <<= (32 - mask_len_bytes * 8)
net &= mask
j += mask_len_bytes
gateway = util.unpack_big_endian(response, j, 4)
j += 4
routes.append((net, mask, gateway))
if j != (i + length + 2):
print("Unable to parse routes")
return routes
def build_dhcp_request(mac_addr, request_broadcast, debug):
"""
Build DHCP request string.
"""
#
# typedef struct _DHCP {
# UINT8 Opcode; /* op: BOOTREQUEST or BOOTREPLY */
# UINT8 HardwareAddressType; /* htype: ethernet */
# UINT8 HardwareAddressLength; /* hlen: 6 (48 bit mac address) */
# UINT8 Hops; /* hops: 0 */
# UINT8 TransactionID[4]; /* xid: random */
# UINT8 Seconds[2]; /* secs: 0 */
# UINT8 Flags[2]; /* flags: 0 or 0x8000 for broadcast*/
# UINT8 ClientIpAddress[4]; /* ciaddr: 0 */
# UINT8 YourIpAddress[4]; /* yiaddr: 0 */
# UINT8 ServerIpAddress[4]; /* siaddr: 0 */
# UINT8 RelayAgentIpAddress[4]; /* giaddr: 0 */
# UINT8 ClientHardwareAddress[16]; /* chaddr: 6 byte eth MAC address */
# UINT8 ServerName[64]; /* sname: 0 */
# UINT8 BootFileName[128]; /* file: 0 */
# UINT8 MagicCookie[4]; /* 99 130 83 99 */
# /* 0x63 0x82 0x53 0x63 */
# /* options -- hard code ours */
#
# UINT8 MessageTypeCode; /* 53 */
# UINT8 MessageTypeLength; /* 1 */
# UINT8 MessageType; /* 1 for DISCOVER */
# UINT8 End; /* 255 */
# } DHCP;
#
# tuple of 244 zeros
# (struct.pack_into would be good here, but requires Python 2.5)
request = [0] * 244
trans_id = gen_trans_id()
# Opcode = 1
# HardwareAddressType = 1 (ethernet/MAC)
# HardwareAddressLength = 6 (ethernet/MAC/48 bits)
for a in range(0, 3):
request[a] = [1, 1, 6][a]
# fill in transaction id (random number to ensure response matches request)
for a in range(0, 4):
request[4 + a] = util.str_to_ord(trans_id[a])
if debug == True:
print("BuildDhcpRequest: transactionId:%s,%04X" % (
util.hex_dump2(trans_id),
util.unpack_big_endian(request, 4, 4)))
if request_broadcast:
# set broadcast flag to true to request the dhcp sever
# to respond to a boradcast address,
# this is useful when user dhclient fails.
request[0x0A] = 0x80;
# fill in ClientHardwareAddress
for a in range(0, 6):
request[0x1C + a] = util.str_to_ord(mac_addr[a])
# DHCP Magic Cookie: 99, 130, 83, 99
# MessageTypeCode = 53 DHCP Message Type
# MessageTypeLength = 1
# MessageType = DHCPDISCOVER
# End = 255 DHCP_END
for a in range(0, 8):
request[0xEC + a] = [99, 130, 83, 99, 53, 1, 1, 255][a]
return array.array("B", request)
