New in version 6.1.


The QUIC protocol integrates encryption, stream multiplexing and flow control at the transport layer. QUIC uses TLS 1.3 by default. Zeek’s QUIC analyzer provides greater observability into the protocols TLS handshake.


An example of a quic.log.

zeek@zeek-6.1:~ zeek -C LogAscii::use_json=T -r chromium-115.0.5790.110-api-cirrus-com.pcap
zeek@zeek-6.1:~ jq . quic.log
  "ts": 1692198386.837988,
  "uid": "CA482y1XJVd3d0RYI7",
  "id.orig_h": "",
  "id.orig_p": 53727,
  "id.resp_h": "",
  "id.resp_p": 443,
  "version": "1",
  "client_initial_dcid": "95412c47018cdfe8",
  "server_scid": "d5412c47018cdfe8",
  "server_name": "api.cirrus-ci.com",
  "client_protocol": "h3",
  "history": "ISisH"

QUIC::Info provides further details on the current output of the quic.log. Current fields include:

  • version: The version of QUIC that was identified.

  • client_initial_dcid: When QUIC initiates a connection it uses Random Number Generators to create the first Destination Connection ID (DCID). This DCID is subsequently used for routing and packet protection by client and server.

  • server_scid: A QUIC supported server responds to a DCID by selecting a Source Connection ID (SCID). This usually occurs within the server’s first INITIAL packet. This is typically used by the client in subsequent packets, although the SCID can change to adapt to new network conditions.

  • client_protocol: If the ClientHello packet is successfully extracted and contains the ALPN extension, the extension’s first entry is placed in client_protocol.

  • history: An experimental feature provides a history of the QUIC protocol usage. In the example above the history outlines:

    • An initial packet from the client (I) - a new connection

    • An TLS ClientHello from the client (S) - the start of a TLS handshake

    • An initial packet from the server (i) - an acknowledgement from the server of the new connection

    • A TLS ServerHello response from the server (s) - the selection of a cipher suite from the options provided by the client

    • A handshake packet from the client (H)


The QUIC analyzer is an initial attempt to provide observability into QUIC network traffic. In Zeek 6.1, although included by default, the QUIC analyzer is still considered experimental. Contributions, feedback and issues can be reported via Github, Slack or the forum.