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Elastic Docs ›Packetbeat Reference [1.3] ›Reference ›Configuration Options

Interfaces

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Interfaces

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The interfaces section configures the sniffer. Here is an example configuration:

# Select the network interfaces to sniff the data. You can use the "any"
# keyword to sniff on all connected interfaces.
interfaces:
  # On which device to sniff
  device: any

  # The maximum capture size of a single packet.
  snaplen: 1514

  # The type of the sniffer to use
  type: af_packet

  # The size of the sniffing buffer
  buffer_size_mb: 100

Sniffing Options

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You can specify the following options in the interfaces section:

device

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The network device to capture traffic from. The specified device is set automatically to promiscuous mode, meaning that Packetbeat can capture traffic from other hosts on the same LAN.

Example:

interfaces:
  device: eth0

On Linux, you can specify any for the device, and Packetbeat captures all messages sent or received by the server where Packetbeat is installed.

When you specify any for the device, the interfaces are not set to promiscuous mode.

The device option also accepts specifying the device by its index in the list of devices available for sniffing. To obtain the list of available devices, run Packetbeat with the following command:

packetbeat -devices

This command returns a list that looks something like the following:

0: en0 (No description available)
1: awdl0 (No description available)
2: bridge0 (No description available)
3: fw0 (No description available)
4: en1 (No description available)
5: en2 (No description available)
6: p2p0 (No description available)
7: en4 (No description available)
8: lo0 (No description available)

The following example sets up sniffing on the first interface in the list:

interfaces:
  device: 0

Specifying the index is especially useful on Windows where device names can be long.

snaplen

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The maximum size of the packets to capture. The default is 65535, which is large enough for almost all networks and interface types. If you sniff on a physical network interface, the optimal setting is the MTU size. On virtual interfaces, however, it’s safer to accept the default value.

Example:

interfaces:
  device: eth0
  snaplen: 1514

type

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Packetbeat supports three sniffer types:

  • pcap, which uses the libpcap library and works on most platforms, but it’s not the fastest option.
  • af_packet, which uses memory-mapped sniffing. This option is faster than libpcap and doesn’t require a kernel module, but it’s Linux-specific.
  • pf_ring, which makes use of an ntop.org project. This setting provides the best sniffing speed, but it requires a kernel module, and it’s Linux-specific.

The default sniffer type is pcap.

Here is an example configuration that specifies the af_packet sniffing type:

interfaces:
  device: eth0
  type: af_packet

On Linux, if you are trying to optimize the CPU usage of Packetbeat, we recommend trying the af_packet and pf_ring options. Read Setting Traffic Capturing Options for more details.

If you use the af_packet sniffer, you can tune its behaviour by specifying the following options:

buffer_size_mb

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The maximum size of the shared memory buffer to use between the kernel and user space. A bigger buffer usually results in lower CPU usage, but consumes more memory. This setting is only available for the af_packet sniffer type. The default is 30 MB.

Example:

interfaces:
  device: eth0
  type: af_packet
  buffer_size_mb: 100

with_vlans

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Packetbeat automatically generates a BPF for capturing only the traffic on ports where it expects to find known protocols. For example, if you have configured port 80 for HTTP and port 3306 for MySQL, Packetbeat generates the following BPF filter: "port 80 or port 3306".

However, if the traffic contains VLAN tags, the filter that Packetbeat generates is ineffective because the offset is moved by four bytes. To fix this, you can enable the with_vlans option, which generates a BPF filter that looks like this: "port 80 or port 3306 or (vlan and (port 80 or port 3306))".

bpf_filter

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Packetbeat automatically generates a BPF for capturing only the traffic on ports where it expects to find known protocols. For example, if you have configured port 80 for HTTP and port 3306 for MySQL, Packetbeat generates the following BPF filter: "port 80 or port 3306".

You can use the bpf_filter setting to overwrite the generated BPF filter. For example:

interfaces:
  device: eth0
  bpf_filter: "net 192.168.238.0/0 and port 80 and port 3306"

This setting disables automatic generation of the BPF filter. If you use this setting, it’s your responsibility to keep the BPF filters in sync with the ports defined in the protocols section.

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