base/protocols/conn/main.zeek

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.zeek

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

Possible conn_state values:

  • 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 (applies to UDP too)
g a content gap
t packet with retransmitted payload
w packet with a zero window advertisement
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 Zeek’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. The ‘a’, ‘d’, ‘i’ and ‘q’ flags are recorded a maximum of one time in either direction regardless of how many are actually seen. ‘f’, ‘h’, ‘r’ and ‘s’ can be recorded multiple times for either direction if the associated sequence number differs from the last-seen packet of the same flag type. ‘c’, ‘g’, ‘t’ and ‘w’ are recorded in a logarithmic fashion: the second instance represents that the event was seen (at least) 10 times; the third instance, 100 times; etc.

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 &optional

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

(present if policy/protocols/conn/mac-logging.zeek is loaded)

Link-layer address of the originator, if available.

resp_l2_addr: string &log &optional

(present if policy/protocols/conn/mac-logging.zeek is loaded)

Link-layer address of the responder, if available.

vlan: int &log &optional

(present if policy/protocols/conn/vlan-logging.zeek is loaded)

The outer VLAN for this connection, if applicable.

inner_vlan: int &log &optional

(present if policy/protocols/conn/vlan-logging.zeek is loaded)

The inner VLAN for this connection, if applicable.

speculative_service: string &log &optional

(present if policy/protocols/conn/speculative-service.zeek is loaded)

Protocol that was determined by a matching signature after the beginning of a connection. In this situation no analyzer can be attached and hence the data cannot be analyzed nor the protocol can be confirmed.

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

Events

Conn::log_conn
Type:event (rec: Conn::Info)

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