"Community ID" flow hashing for Zeek

This Zeek package provides support for "community ID" flow hashing, a standardized way of labeling traffic flows in network monitors. When loaded, the package adds a community_id string field to conn.log. This is work in progress between the Zeek and Suricata communities, to enable correlation of flows in the outputs of both tools. Feedback is very welcome, also from users/developers of other monitoring software.

This package implements a BiF to implement the hashing logic and thus needs binary compilation, so it's also a Zeek plugin. Here's an example of a resulting conn.log:

#separator \x09
#set_separator  ,
#empty_field    (empty)
#unset_field    -
#path   conn
#open   2018-01-31-13-06-56
#fields ts      uid     id.orig_h       id.orig_p       id.resp_h       id.resp_p       proto   service duration        orig_bytes      resp_bytes      conn_state      local_orig      local_resp      missed_bytes    history orig_pkts       orig_ip_bytes   resp_pkts       resp_ip_bytes   tunnel_parents  community_id
#types  time    string  addr    port    addr    port    enum    string  interval        count   count   string  bool    bool    count   string  count   count   count   count   set[string]     string
1071580904.891921       CPcWB54kqKkvkdNEXe      128.232.110.120 34855   66.35.250.204   80      tcp     -       0.311104        496     1731    SF      -       -       2227    ShADadfF        6       816     6       2051    -       1:LQU9qZlK+B5F3KDmev6m5PMibrg=
#close  2018-01-31-13-06-56

Protocol support

The Community ID spec currently envisions support for a number of protocol constellations for which Zeek does not track flow-level state because its analyzers wouldn't know what to do with the traffic. For such flows Zeek never triggers the connection-related events used by the package, so there won't be output in conn.log anyway. (If there were protocols Zeek tracks at the flow level but the plugin doesn't support, the reported ID would be empty.) We currently support TCP and UDP over IPv4 or IPv6, as well as ICMPv4 and ICMPv6. We do not support other transport-level protocols (such as SCTP), or general IP-address-pair flows for unsupported transport layer protocols.

Using the package

The package's name is zeek-community-id; the plugin's name is Corelight::CommunityID. You can see the package's configuration options in the corresponding Zeek script.

Compatibility with Zeek versions

The Community ID package works with any Zeek version since 2.6.4. Since the Zeek codebase has undergone substantial changes since then, the package provides compatibility branches that support specific Zeek version ranges, striking a balance between readable code vs. ease of installation and branch management.

On the zeek/x.y and master branches, git tags label the Community ID releases. For example, 3.1.0 is the first release on the zeek/3.1 branch, and works with any Zeek in the 3.1 series. The next Community ID release for the Zeek 3.1 series will be called 3.1.1 and also live on this branch.

Each branch also declares a Zeek version compatibility window in zkg.meta, so won't install if paired with an incompatible Zeek version. For example, the master branch currently requires at least Zeek 3.2.0, with no upper bound.

Here's a summary of how Zeek versions, git tags, and git branches line up:

Zeek version	Git tag	Git branch
2.6.4 - 3.0.x	3.0.y	zeek/3.0
3.1.x	3.1.y	zeek/3.1
3.2.x - master	3.2.y	master

Testing

The package includes btests that verify plugin loading and crunch included test pcaps through Zeek to check baselined Zeek console output. You can run these by saying btest -c btest.cfg in the tests directory.

Contact

For questions and feedback, please get in touch on Zeek mailing list or the Zeek Slack. Github issues and PRs are welcome.