UDP (im_udp)

This module accepts UDP datagrams on the configured address and port. UDP is the transport protocol of the legacy BSD Syslog as described in RFC 3164, so this module can be particularly useful to receive such messages from older devices that do not support other transports.

To examine the supported platforms, see the list of installer packages in the Available Modules chapter.

UDP is an unreliable transport protocol and does not guarantee delivery. Messages may not be received or may be truncated. It is recommended to use the TCP or SSL transport modules instead, if possible.

To reduce the likelihood of message loss, consider:

increasing the socket buffer size with SockBufSize,
raising the route priority by setting the Priority directive (to a low number such as 1), and
adding additional buffering by increasing the LogqueueSize or adding a pm_buffer instance.

This module does not provide access control. Firewall rules can be used to deny connections from certain hosts.

For parsing syslog messages, see the parse_syslog_bsd() procedure of the xm_syslog module.

Configuration

The im_udp module accepts the following directives in addition to the common module directives.

Optional directives

ListenAddr

The module accepts connections on the IP address or hostname and port defined here. The default address is localhost and the default port is 514. The port number can be defined by appending it at the end of the hostname or IP address using a colon as a separator (host:port). The port section of this directive and the Port directive are mutually exclusive. In case both are defined, the port number defined here takes precedence over a port defined in the Port directive. In case none of them is defined, the default port 514 is used.

To listen on multiple addresses or ports in a single module instance, this directive can be repeated multiple times. Both IPv4 and IPv6 addresses are supported. If a DNS name is used, the number of addresses or cnames should be kept below 16 to avoid potential issues caused by DNS response size limits.

Formerly called Host, this directive is now ListenAddr. Host will become deprecated from NXLog EE 6.0.

When the Host directive is used with a hostname instead of an IP address, the hostname will be resolved to an IP address for each new connection. If a resolver, e.g. DNS, returns multiple IP addresses, the module will connect to the first IP address. If a single output instance is configured with multiple Host directives or the resolver returns multiple addresses for a name, these hosts are accessed in failover mode. If a Host directive is configured with a hostname, the product performs a name lookup and establishes the connection to the first reachable address in the returned set of addresses. The module will remain connected to that address until it is stopped, or the connection is severed. DNS changes are therefore not picked up by the module without intervention. If the connection fails to the first address of the set, the module will attempt to connect to the next address, until it reaches the end of the set of addresses. Then it performs a lookup on the next Host directive, if so configured. Once all options are exhausted, the module will start over from the first Host directive, cycling through them again until the connection can be re-established.

Port

The module will listen for incoming connections on this port number. The default is port 514.

The Port directive will become deprecated from NXLog EE 6.0. After that, the port can only be defined in the ListenAddr directive.

AllowIP

This optional directive can be used to allow IP addresses and/or networks to connect. The directive can be set multiple times to add different IPs or networks to allow. This directive is only active when the ListenAddr directive is present. In the absence of this directive, the BlockIP directive is considered. If both AllowIP and BlockIP are absent, then hosts are not restricted from connecting to a listening module.

The following formats may be used for the AllowIP directive:

0.0.0.0 (IPv4 address)
0.0.0.0/32 (IPv4 network with subnet bits)
0.0.0.0/0.0.0.0 (IPv4 network with subnet address)
aa::1 (IPv6 address)
aa::12/64 (IPv6 network with subnet bits)

BlockIP

This optional directive can be used to deny IP addresses and/or networks to connect. The directive can be set multiple times to add different IPs or networks to deny. This directive is only active when the ListenAddr directive is present. In the absence of this directive, the AllowIP directive is considered. If both AllowIP and BlockIP are absent, then hosts are not restricted from connecting to a listening module.

The following formats may be used for the BlockIP directive:

0.0.0.0 (IPv4 address)
0.0.0.0/32 (IPv4 network with subnet bits)
0.0.0.0/0.0.0.0 (IPv4 network with subnet address)
aa::1 (IPv6 address)
aa::12/64 (IPv6 network with subnet bits)

ExclusiveAddrUse

This optional boolean directive specifies whether the module instance should exclusively bind to the specified port. The default value is FALSE; multiple module instances can bind to the same port.

This directive is only supported on Windows platforms.

ReuseAddr

This optional boolean directive determines whether the module instance should forcibly bind to a port already in use. The default value is TRUE; multiple instances can listen on the same port and process data simultaneously.

ReusePort

This optional boolean directive specifies whether multiple im_udp module instances can listen on the same port. When you enable this directive, multiple instances run in a separate thread, allowing NXLog to process incoming logs simultaneously. See the examples below. The default value is FALSE; multiple instances cannot bind to the same port.

This directive is not supported on Windows platforms.

SockBufSize

This optional directive sets the socket buffer size (SO_RCVBUF) to the value specified. If not set, the operating system defaults are used. If UDP packet loss is occurring at the kernel level, setting this to a high value (such as 150000000) may help. On Windows systems, the default socket buffer size is extremely low, and using this option is highly recommended.

UseRecvmmsg

This boolean directive specifies that the recvmmsg() system call should be used, if available, to receive multiple messages per call to improve performance. The default is TRUE.

Fields

The following fields are used by im_udp.

$raw_event (type: string): The received string.

$MessageSourceAddress (type: ipaddr): The IP address of the remote host.

Examples

Example 1. Using the im_udp module

This configuration accepts log messages via UDP and writes them to a file.

nxlog.conf

<Input udp>
    Module        im_udp
    ListenAddr    192.168.1.1:514
</Input>

<Output file>
    Module        om_file
    File          "tmp/output"
</Output>

<Route udp_to_file>
    Path          udp => file
</Route>

Example 2. Reusing a single port by multiple module instances

The configuration below provides two im_udp module instances to reuse port 514 via the ReusePort directive. Received messages are written to the /tmp/output file.

nxlog.conf

<Input udp_one>
    Module        im_udp
    ListenAddr    192.168.1.1:514
    ReusePort     TRUE
</Input>

<Input udp_two>
    Module        im_udp
    ListenAddr    192.168.1.1:514
    ReusePort     TRUE
</Input>

<Output file>
    Module        om_file
    File          "tmp/output"
</Output>

<Route udp_to_file>
    Path          udp_one, udp_two => file
</Route>