def __parse(self):
self.parsed = True
try:
# Check last two bytes of byte payload - if they are set to zero we don't have any path attributes
if struct.unpack("!H", self.payload[-2:])[0] == 0:
self.path_attributes_length = 0
# Unpack the length of withdrawn routes field and add 2 bytes to the current byte marker position
self.withdrawn_routes_length = struct.unpack(
"!H", self.payload[:2])[0]
current_byte_position = 2
# Start parsing withdrawn routes
if self.withdrawn_routes_length is not 0:
continue_loop = True
# Loop through withdrawals
while continue_loop:
# First of all we need to parse the length of the withdrawn prefix. Depending on the prefix length
# we can determine the length following prefix itself
prefix_length_bytes = self.payload[
current_byte_position:current_byte_position + 1]
prefix_length = struct.unpack("!B", prefix_length_bytes)[0]
current_byte_position += 1
if 0 <= prefix_length <= 8:
# Length of prefix field: 1 Byte
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 1]
current_byte_position += 1
elif 9 <= prefix_length <= 16:
# Length of prefix field: 2 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 2]
current_byte_position += 2
elif 17 <= prefix_length <= 24:
# Length of prefix field: 3 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 3]
current_byte_position += 3
elif 25 <= prefix_length:
# Length of prefix field: 4 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 4]
current_byte_position += 4
else:
self.error = True
raise BGPWithdrawnPrefixError(
"can't match prefix length.")
# Add BGPRoute object with information about the withdrawn route to list
self.withdrawn_routes.append(
BGPRoute.from_binary(prefix_bytes,
prefix_length_bytes))
# Check if we are at the end of the payload
if self.withdrawn_routes_length <= current_byte_position:
# If yes we need to stop the iteration
continue_loop = False
# Second step: Continue with the path attributes
if self.path_attributes_length is None:
# First of all get the attributes length field and update the current byte position
self.path_attributes_length = struct.unpack(
"!H",
self.payload[current_byte_position:current_byte_position +
2])[0]
current_byte_position += 2
# Now we have a correct path_attributes_length stored. If this length is zero we don't need to do anything
if self.path_attributes_length is not 0:
continue_loop = True
# Loop through path attributes
while continue_loop:
# Now comes a tricky part of UPDATE message parsing. Each path attribute has a flag bitfield.
# One of those flags is called 'extended length'. If it's set to 1 the following attribute fields
# are 2 bytes long. But if it's set to zero it's just 1 byte long ...
# So first of all: Flag parsing!
attribute_flags = BGPUpdateFlags(
struct.unpack(
"!B", self.payload[
current_byte_position:current_byte_position +
1])[0])
current_byte_position += 1
if attribute_flags.length:
# We got an extended length flag
attribute_fields = struct.unpack(
"!BH", self.payload[
current_byte_position:current_byte_position +
3])
current_byte_position += 3
else:
# We got a normal length flag
attribute_fields = struct.unpack(
"!BB", self.payload[
current_byte_position:current_byte_position +
2])
current_byte_position += 2
# Finally assign the variables
attribute_type = attribute_fields[0]
attribute_length = attribute_fields[1]
# Now we are using the factory pattern again to determine
# which kind of attribute we have to add the list
self.path_attributes.append(
BGPPathAttribute.factory(
attribute_type, self.payload[
current_byte_position:current_byte_position +
attribute_length], attribute_flags))
# Add length of attribute to position pointer
current_byte_position += attribute_length
# Check if there are further path attributes to parse
if current_byte_position >= self.path_attributes_length:
continue_loop = False
# Third step: NLRIs
if len(self.payload) > (self.path_attributes_length + 4 +
self.withdrawn_routes_length):
continue_loop = True
# The four bytes that get added to the attributes and routes length are the two two-byte fields
# for path attribute length and withdrawn routes length
current_byte_position = self.path_attributes_length + 4 + self.withdrawn_routes_length
while continue_loop:
# First of all we have to check the prefix length as byte-length of the following
# prefix depends on its prefix length (This is a 1-byte-field)
prefix_length_bytes = self.payload[
current_byte_position:current_byte_position + 1]
prefix_length = struct.unpack("!B", prefix_length_bytes)[0]
current_byte_position += 1
if 0 <= prefix_length <= 8:
# Length of prefix field: 1 Byte
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 1]
current_byte_position += 1
elif 9 <= prefix_length <= 16:
# Length of prefix field: 2 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 2]
current_byte_position += 2
elif 17 <= prefix_length <= 24:
# Length of prefix field: 3 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 3]
current_byte_position += 3
elif 25 <= prefix_length:
# Length of prefix field: 4 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 4]
current_byte_position += 4
else:
self.error = True
raise BGPWithdrawnPrefixError(
"can't match prefix length.")
try:
self.nlri.append(
BGPRoute.from_binary(prefix_bytes,
prefix_length_bytes))
except BGPError as e:
raise BGPNLRIError(
"can't append NLRI to message (error: " + str(e) +
")")
if current_byte_position >= len(self.payload):
continue_loop = False
# Determine sub-type for filtering
# Using bit flags for easier assignment
if len(self.nlri) > 0:
self.subtype = (self.subtype | BGPStatics.UPDATE_TYPE_ANNOUNCE)
if len(self.withdrawn_routes) > 0:
self.subtype = (self.subtype
| BGPStatics.UPDATE_TYPE_WITHDRAWAL)
except BGPWithdrawnPrefixError as p:
self.error = True
logging.info(p)
except Exception as e:
self.error = True
self.error = False
def __parse(self):
self.parsed = True
try:
# Unpack the length of withdrawn routes field and add 2 bytes to the current byte marker position
self.withdrawn_routes_length = struct.unpack(
"!H", self.payload[:2])[0]
current_byte_position = 2
# Start parsing withdrawn routes
if self.withdrawn_routes_length is not 0:
continue_loop = True
# Loop through withdrawals
while continue_loop:
# AddPath assumption? look for description in the method for NLRI parsing
if self.flags["addpath"].get_value(
) == 0: # No AddPath messages
pass
else:
pathId_length_bytes = self.payload[
current_byte_position:current_byte_position + 4]
pathId = struct.unpack("!I", pathId_length_bytes)[0]
if self.flags["addpath"].get_value(
) == 1: # Only AddPath
self.add_path = True
self.path_id = pathId
current_byte_position += 4
else: # Try to find out (using metric)
if pathId < 65536:
self.add_path = True
self.path_id = pathId
current_byte_position += 4
#else: drop the Path Id, its likely that this is not an AddPath msg
# First of all we need to parse the length of the withdrawn prefix. Depending on the prefix length
# we can determine the length following prefix itself
prefix_length_bytes = self.payload[
current_byte_position:current_byte_position + 1]
prefix_length = struct.unpack("!B", prefix_length_bytes)[0]
current_byte_position += 1
if prefix_length == 0:
prefix_bytes = prefix_length_bytes
elif 0 < prefix_length <= 8:
# Length of prefix field: 1 Byte
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 1]
current_byte_position += 1
elif 9 <= prefix_length <= 16:
# Length of prefix field: 2 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 2]
current_byte_position += 2
elif 17 <= prefix_length <= 24:
# Length of prefix field: 3 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 3]
current_byte_position += 3
elif 25 <= prefix_length:
# Length of prefix field: 4 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 4]
current_byte_position += 4
else:
self.error = True
raise BGPWithdrawnPrefixError(
"can't match prefix length.")
# Add BGPRoute object with information about the withdrawn route to list
self.withdrawn_routes.append(
BGPRoute.from_binary(prefix_bytes,
prefix_length_bytes))
# Check if we are at the end of the payload
if self.withdrawn_routes_length <= current_byte_position:
# If yes we need to stop the iteration
continue_loop = False
# Second step: Continue with the path attributes
if self.path_attributes_length is None:
# First of all get the attributes length field and update the current byte position
self.path_attributes_length = struct.unpack(
"!H",
self.payload[current_byte_position:current_byte_position +
2])[0]
current_byte_position += 2
# Now we have a correct path_attributes_length stored. If this length is zero we don't need to do anything
if self.path_attributes_length is not 0:
continue_loop = True
# Loop through path attributes
while continue_loop:
# Now comes a tricky part of UPDATE message parsing. Each path attribute has a flag bitfield.
# One of those flags is called 'extended length'. If it's set to 1 the following attribute fields
# are 2 bytes long. But if it's set to zero it's just 1 byte long ...
# So first of all: Flag parsing!
attribute_flags = BGPUpdateFlags(
struct.unpack(
"!B", self.payload[
current_byte_position:current_byte_position +
1])[0])
current_byte_position += 1
if attribute_flags.length:
# We got an extended length flag
attribute_fields = struct.unpack(
"!BH", self.payload[
current_byte_position:current_byte_position +
3])
current_byte_position += 3
else:
# We got a normal length flag
attribute_fields = struct.unpack(
"!BB", self.payload[
current_byte_position:current_byte_position +
2])
current_byte_position += 2
# Finally assign the variables
attribute_type = attribute_fields[0]
attribute_length = attribute_fields[1]
# Now we are using the factory pattern again to determine
# which kind of attribute we have to add the list
self.path_attributes.append(
BGPPathAttribute.factory(
attribute_type, self.payload[
current_byte_position:current_byte_position +
attribute_length], attribute_flags))
# Add length of attribute to position pointer
current_byte_position += attribute_length
# Check if there are further path attributes to parse
if current_byte_position >= self.path_attributes_length:
continue_loop = False
# Third step: NLRIs
if len(self.payload) > (self.path_attributes_length + 4 +
self.withdrawn_routes_length):
continue_loop = True
# The four bytes that get added to the attributes and routes length are the two two-byte fields
# for path attribute length and withdrawn routes length
current_byte_position = self.path_attributes_length + 4 + self.withdrawn_routes_length
while continue_loop:
"""
The Following is a Fix for missing Add_Path feature.
Due to the lack of a definition for this case, we need depend on the users decision.
See RFC 7911 Chapter 6 p.5 (22.07.2020).
In most cases, the pathId is lower than 2**16. Also it is uncommon,
that one BGP UPDATE message contains the 0.0.0.0/0 prefix 2 times.
This leads to the following metric if the user sets the add_path_flag to 2.
"""
# AddPath assumption?
if self.flags["addpath"].get_value(
) == 0: # No AddPath messages
pass
else:
pathId_length_bytes = self.payload[
current_byte_position:current_byte_position + 4]
pathId = struct.unpack("!I", pathId_length_bytes)[0]
if self.flags["addpath"].get_value(
) == 1: # Only AddPath
self.add_path = True
self.path_id = pathId
current_byte_position += 4
else: # Try to find out (using metric)
if pathId < 65536:
self.add_path = True
self.path_id = pathId
current_byte_position += 4
#else: drop the Path Id, its likely that this is not an AddPath msg
# First of all we have to check the prefix length as byte-length of the following
# prefix depends on its prefix length (This is a 1-byte-field)
prefix_length_bytes = self.payload[
current_byte_position:current_byte_position + 1]
prefix_length = struct.unpack("!B", prefix_length_bytes)[0]
current_byte_position += 1
if prefix_length == 0: #0.0.0.0/0
prefix_bytes = prefix_length_bytes
elif 0 <= prefix_length <= 8:
# Length of prefix field: 1 Byte
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 1]
current_byte_position += 1
elif 9 <= prefix_length <= 16:
# Length of prefix field: 2 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 2]
current_byte_position += 2
elif 17 <= prefix_length <= 24:
# Length of prefix field: 3 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 3]
current_byte_position += 3
elif 25 <= prefix_length:
# Length of prefix field: 4 Bytes
prefix_bytes = self.payload[
current_byte_position:current_byte_position + 4]
current_byte_position += 4
else:
self.error = True
raise BGPWithdrawnPrefixError(
"can't match prefix length.")
try:
self.nlri.append(
BGPRoute.from_binary(prefix_bytes,
prefix_length_bytes))
except BGPError as e:
raise BGPNLRIError(
"can't append NLRI to message (error: " + str(e) +
")")
if current_byte_position >= len(self.payload):
continue_loop = False
# Determine sub-type for filtering
# Using bit flags for easier assignment
if len(self.nlri) > 0:
self.subtype = (self.subtype | BGPStatics.UPDATE_TYPE_ANNOUNCE)
if len(self.withdrawn_routes) > 0:
self.subtype = (self.subtype
| BGPStatics.UPDATE_TYPE_WITHDRAWAL)
except BGPWithdrawnPrefixError as p:
self.error = True
logging.info(p)
except Exception as e:
self.error = True
self.error = False
