James Butler James Butler - 3 months ago 32
Python Question

Scapy BGP Flags Attribute

Is there any other way I could use Scapy to configure a packet with multiple flag attributes?

I am trying to set up a BGP Layer with both optional and transitive attributes. I am using this github file: https://github.com/levigross/Scapy/blob/master/scapy/contrib/bgp.py. On line 107, is the flags I am trying to add.

Past failed attempts include:

>>>a=BGPPathAttribute(flags=["Optional","Transitive"])
>>>send(a)
TypeError: unsupported operand type(s) for &: 'str' and 'int'

>>>a=BGPPathAttribute(flags=("Optional","Transitive"))
>>>send(a)
TypeError: unsupported operand type(s) for &: 'tuple' and 'int'

>>>a=BGPPathAttribute(flags="Optional")/BGPPathAttribute(flags="Transitive")
Creates 2 separate path attributes: One which is Optional and Non-Transitive and the other which is Well Known and Transitive.

>>>a=BGPPathAttribute(flags="Optional", flags="Transitive")
SyntaxError: keyword argument repeated

>>>a=BGPPathAttribute(flags="OT")
ValueError: ['OT'] is not in list

Answer

It is possible to configure multiple flag attributes by enumerating them in a single string, delimited with the '+' sign:

In [1]: from scapy.all import *
WARNING: No route found for IPv6 destination :: (no default route?)

In [2]: from scapy.contrib.bgp import BGPPathAttribute

In [3]: BGPPathAttribute(flags='Optional+Transitive')
Out[3]: <BGPPathAttribute  flags=Transitive+Optional |>

In [4]: send(_)
WARNING: Mac address to reach destination not found. Using broadcast.
.
Sent 1 packets.

An alternative method, to directly calculate the numerical value of the desired combination of flags, is provided for completeness' sake:

In [1]: from scapy.all import *
WARNING: No route found for IPv6 destination :: (no default route?)

In [2]: from scapy.contrib.bgp import BGPPathAttribute

In [3]: BGPPathAttribute(flags='Optional').flags | BGPPathAttribute(flags='Transitive').flags
Out[3]: 192

In [4]: BGPPathAttribute(flags=_)
Out[4]: <BGPPathAttribute  flags=Transitive+Optional |>

In [5]: send(_)
WARNING: Mac address to reach destination not found. Using broadcast.
.
Sent 1 packets.