Zeek::AF_Packet

This plugin provides native AF_Packet support for Zeek (http://man7.org/linux/man-pages/man7/packet.7.html).

Installation

Before installing the plugin, make sure the kernel headers are installed and your kernel supports PACKET_FANOUT [1] and TPACKET_V3.

Package Manager

The plugin is available as package for the Zeek Package Manager and can be installed using the following command:

zkg install zeek-af_packet-plugin

Manual Install

The following will compile and install the AF_Packet plugin alongside Zeek, assuming it can find the kernel headers in a standard location:

# ./configure && make && make install

If the headers are installed somewhere non-standard, add --with-kernel=<kernel-header-directory> to the configure command. Furthermore, --with-latest-kernel will use the latest headers available instead of looking for the headers matching the running kernel's version. If everything built and installed correctly, you should see this:

# zeek -NN Zeek::AF_Packet
Zeek::AF_Packet - Packet acquisition via AF_Packet (dynamic, version 3.0.1)
[Packet Source] AF_PacketReader (interface prefix "af_packet"; supports live input)
[Type] AF_Packet::FanoutMode
[Constant] AF_Packet::buffer_size
[Constant] AF_Packet::enable_hw_timestamping
[Constant] AF_Packet::enable_fanout
[Constant] AF_Packet::enable_defrag
[Constant] AF_Packet::fanout_mode
[Constant] AF_Packet::fanout_id

[1]	Note that some kernel versions between 3.10 and 4.7 might exhibit a bug that prevents the required symmetric hashing. The script available at https://github.com/JustinAzoff/can-i-use-afpacket-fanout can be used to verify whether PACKET_FANOUT works as expected.

Upgrade from Bro to Zeek

In the context of the transition from Bro to Zeek, the plugin has been renamed. To upgrade from the Bro-version of the plugin, just remove the old version and then install the renamed one. Using the package manager the following will uninstall the old version of the plugin:

# zkg remove bro-af_packet-plugin

For manually installed plugins, remove the corresponding plugin directory:

# rm -rf <path_to_zeek>/lib/bro/plugins/Bro_AF_Packet/

Usage

Once installed, you can use AF_Packet interfaces/ports by prefixing them with af_packet:: on the command line. For example, to use AF_Packet to monitor interface eth0:

# zeek -i af_packet::eth0

To use AF_Packet, running Zeek without root privileges, the Zeek processes need the CAP_NET_RAW capability. You can set it with the following command (on each sensor, after zeekctl install):

# setcap cap_net_raw+eip <path_to_zeek>/bin/zeek

The AF_Packet plugin automatically enables promiscuous mode on the interfaces. As the plugin is using PACKET_ADD_MEMBERSHIP to enter the promiscuous mode without interfering others, the PROMISC flag is not touched. To verify that the interface entered promiscuous mode you can use dmesg.

To adapt the plugin to your needs, you can set a couple of parameters like buffer size. See scripts/init.zeek for the default values.

Usage with zeekctl

To use the AF_Packet plugin with zeekctl, the custom load balance method can be utilized. The following shows an exemplary configuration:

[manager]
type=manager
host=localhost

[proxy-1]
type=proxy
host=localhost

[worker-1]
type=worker
host=localhost
interface=af_packet::eth0
lb_method=custom
lb_procs=8
pin_cpus=0,1,2,3,4,5,6,7
# Optional parameters for per node configuration:
af_packet_fanout_id=23
af_packet_fanout_mode=AF_Packet::FANOUT_HASH
af_packet_buffer_size=128*1024*1024

If all interfaces using lb_method=custom should be configured for AF_Packet, the prefix can be globally definied by adding the following line to zeekctl.conf:

lb_custom.InterfacePrefix=af_packet::

Limitations

• Even using AF_Packet's ETH_P_ALL, the kernel removes VLAN tags. While the tags are provided spereately, there is no efficient way to pass them to Zeek.