TCP Chain

This module contains the TCPChain flow analysis chain which can be used by PATHspider’s Observer for recording basic TCP [RFC793] behaviour details. This module also contains a helper function that may be used by chains for the parsing of TCP options and a number of useful TCP related constants that can be used to interpret the results added to flow records by TCPChain.

class pathspider.chains.tcp.TCPChain[source]

This flow analysis chain records details of basic TCP behaviour in the flow record. It will determine when a 3WHS has completed and has simplified logic for determining when a TCP flow has completed.

Field Name

Type

Description

tcp_synflags_fwd

int

SYN flags seen in the forward direction

tcp_synflags_rev

int

SYN flags seen in the reverse direction

tcp_fin_fwd

bool

At least one FIN flag was seen in the forward direction

tcp_fin_rev

bool

At least one FIN flag was seen in the reverse direction

tcp_rst_fwd

bool

At least one RST flag was seen in the forward direction

tcp_rst_rev

bool

At least one RST flag was seen in the reverse direction

tcp_connected

bool

The 3WHS completed
new_flow(rec, ip)[source]

For a new flow, all fields will be initialised to False except tcp_synflags_* which will be set to None.

Parameters

  • rec (dict) – the flow record

  • ip (plt.ip or plt.ip6) – the IP or IPv6 packet that triggered the creation of a new flow record

Returns

Always True

Return type

bool

tcp(rec, tcp, rev)[source]

Records basic TCP behaviour details.

SYN Flags

This will record the SYN flags observed in each direction. These will not be recorded again if there are futher segments in the flow with a SYN bit set, the first SYN observed wins.

FIN and RST Flags

If a segment has the FIN or RST flags, the relevant fields are set to true.

3WHS

If a SYN was observed in the forward direction, and a SYNACK in the reverse direction and the segment passed is an ACK in the forward direction then tcp_connected will be set to True.

Flow Completion

If a FIN has been observed in one direction and this segment contains a FIN in the other direction, a flow is considered complete. If a RST has been observed in either direction, a flow is considered complete.

Parameters

  • rec (dict) – the flow record

  • tcp – the TCP segment that was observed to be part of this flow

  • rev (bool) – True if the packet was in the reverse direction, False if in the forward direction

Returns

True if flow should continue to be observed, False if the flow should be passed on for merging (i.e. the flow is complete)

Return type

bool

pathspider.chains.tcp.TCP_ACK = 16

TCP Flag - ACK

pathspider.chains.tcp.TCP_CWR = 128

TCP Flag - CWR

pathspider.chains.tcp.TCP_ECE = 64

TCP Flag - ECE

pathspider.chains.tcp.TCP_FIN = 1

TCP Flag - FIN

pathspider.chains.tcp.TCP_PSH = 8

TCP Flag - PSH

pathspider.chains.tcp.TCP_RST = 4

TCP Flag - RST

pathspider.chains.tcp.TCP_SA = 18

TCP Flags - SYN and ACK

pathspider.chains.tcp.TCP_SAE = 82

TCP Flags - SYN, ACK, ECE

pathspider.chains.tcp.TCP_SAEC = 210

TCP Flags - SYN, ACK, ECE and CWR

pathspider.chains.tcp.TCP_SEC = 194

TCP Flags - SYN, ACK and ECE

pathspider.chains.tcp.TCP_SYN = 2

TCP Flag - SYN

pathspider.chains.tcp.TCP_URG = 32

TCP Flag - URG

pathspider.chains.tcp.TO_EOL = 0

TCP Option - End of options list

pathspider.chains.tcp.TO_EXID_FASTOPEN = (249, 137)

TCP Option Experiment ID - TCP Fast Open

pathspider.chains.tcp.TO_EXPA = 254

TCP Option - Experimental Option A

pathspider.chains.tcp.TO_EXPB = 255

TCP Option - Experimental Option B

pathspider.chains.tcp.TO_FASTOPEN = 34

TCP Option - TCP Fast Open Cookie

pathspider.chains.tcp.TO_MPTCP = 30

TCP Option - Multipath TCP

pathspider.chains.tcp.TO_MSS = 2

TCP Option - Maximum Segment Size

pathspider.chains.tcp.TO_NOP = 1

TCP Option - No Operation

pathspider.chains.tcp.TO_SACK = 5

TCP Option - Selective Acknowledgement

pathspider.chains.tcp.TO_SACKOK = 4

TCP Option - Selective Acknowledgement Permitted

pathspider.chains.tcp.TO_TS = 8

TCP Option - Timestamp

pathspider.chains.tcp.TO_WS = 3

TCP Option - Window Scaling

pathspider.chains.tcp.tcp_options(tcp)[source]

Parses and extracts TCP options from a python-libtrace TCP object.

Warning

This is a pure Python implementation of a TCP options parser and does not benefit from the speed advantage generally realised by calling to libtrace functions written in C through python-libtrace.

Parameters

tcp (plt.tcp) – The TCP header to extract options from

Returns

A mapping of option kinds to values

Return type

dict