base/protocols/conn/main.bro

Conn

This script manages the tracking/logging of general information regarding TCP, UDP, and ICMP traffic. For UDP and ICMP, “connections” are to be interpreted using flow semantics (sequence of packets from a source host/port to a destination host/port). Further, ICMP “ports” are to be interpreted as the source port meaning the ICMP message type and the destination port being the ICMP message code.

Namespace:	Conn
Imports:	base/utils/site.bro
Source File:	`/scripts/base/protocols/conn/main.bro`

Summary

Types

Conn::Info: record The record type which contains column fields of the connection log.

Redefinitions

`Log::ID`: `enum`	The connection logging stream identifier.
`connection`: `record`

Events

Conn::log_conn: event Event that can be handled to access the Conn::Info record as it is sent on to the logging framework.

Detailed Interface

Types

Conn::Info

Type:

record

ts: time &log

This is the time of the first packet.

uid: string &log

A unique identifier of the connection.

id: conn_id &log

The connection’s 4-tuple of endpoint addresses/ports.

proto: transport_proto &log

The transport layer protocol of the connection.

service: string &log &optional

An identification of an application protocol being sent over the connection.

duration: interval &log &optional

How long the connection lasted. For 3-way or 4-way connection tear-downs, this will not include the final ACK.

orig_bytes: count &log &optional

The number of payload bytes the originator sent. For TCP this is taken from sequence numbers and might be inaccurate (e.g., due to large connections).

resp_bytes: count &log &optional

The number of payload bytes the responder sent. See orig_bytes.

conn_state: string &log &optional

conn_state	Meaning
S0	Connection attempt seen, no reply.
S1	Connection established, not terminated.
SF	Normal establishment and termination. Note that this is the same symbol as for state S1. You can tell the two apart because for S1 there will not be any byte counts in the summary, while for SF there will be.
REJ	Connection attempt rejected.
S2	Connection established and close attempt by originator seen (but no reply from responder).
S3	Connection established and close attempt by responder seen (but no reply from originator).
RSTO	Connection established, originator aborted (sent a RST).
RSTR	Responder sent a RST.
RSTOS0	Originator sent a SYN followed by a RST, we never saw a SYN-ACK from the responder.
RSTRH	Responder sent a SYN ACK followed by a RST, we never saw a SYN from the (purported) originator.
SH	Originator sent a SYN followed by a FIN, we never saw a SYN ACK from the responder (hence the connection was “half” open).
SHR	Responder sent a SYN ACK followed by a FIN, we never saw a SYN from the originator.
OTH	No SYN seen, just midstream traffic (a “partial connection” that was not later closed).

local_orig: bool &log &optional

If the connection is originated locally, this value will be T. If it was originated remotely it will be F. In the case that the Site::local_nets variable is undefined, this field will be left empty at all times.

local_resp: bool &log &optional

If the connection is responded to locally, this value will be T. If it was responded to remotely it will be F. In the case that the Site::local_nets variable is undefined, this field will be left empty at all times.

missed_bytes: count &log &default = 0 &optional

Indicates the number of bytes missed in content gaps, which is representative of packet loss. A value other than zero will normally cause protocol analysis to fail but some analysis may have been completed prior to the packet loss.

history: string &log &optional

Records the state history of connections as a string of letters. The meaning of those letters is:

Letter	Meaning
s	a SYN w/o the ACK bit set
h	a SYN+ACK (“handshake”)
a	a pure ACK
d	packet with payload (“data”)
f	packet with FIN bit set
r	packet with RST bit set
c	packet with a bad checksum
t	packet with retransmitted payload
i	inconsistent packet (e.g. FIN+RST bits set)
q	multi-flag packet (SYN+FIN or SYN+RST bits set)
^	connection direction was flipped by Bro’s heuristic

If the event comes from the originator, the letter is in upper-case; if it comes from the responder, it’s in lower-case. Multiple packets of the same type will only be noted once (e.g. we only record one “d” in each direction, regardless of how many data packets were seen.)

orig_pkts: count &log &optional

Number of packets that the originator sent. Only set if use_conn_size_analyzer = T.

orig_ip_bytes: count &log &optional

Number of IP level bytes that the originator sent (as seen on the wire, taken from the IP total_length header field). Only set if use_conn_size_analyzer = T.

resp_pkts: count &log &optional

Number of packets that the responder sent. Only set if use_conn_size_analyzer = T.

resp_ip_bytes: count &log &optional

Number of IP level bytes that the responder sent (as seen on the wire, taken from the IP total_length header field). Only set if use_conn_size_analyzer = T.

tunnel_parents: set [string] &log

If this connection was over a tunnel, indicate the uid values for any encapsulating parent connections used over the lifetime of this inner connection.

orig_l2_addr: string &log &optional