UDP with IP Spoofing (om_udpspoof)
This module sends log messages as UDP datagrams to the address and port specified and allows the source address in the UDP packet to be spoofed to make the packets appear as if they were sent from another host. This is particularly useful in situations where log data needs to be forwarded to another server and the server uses the client address to identify the data source. With IP spoofing the UDP packets will contain the IP address of the originating client that produced the message instead of the forwarding server.
This module is very similar to the om_udp module and can be used as a drop-in replacement. The SpoofAddress configuration directive can be used to set the address if necessary. The UDP datagram will be sent with the local IP address if the IP address to be spoofed is invalid. The source port in the UDP datagram will be set to the port number of the local connection (the port number is not spoofed).
The network input modules (im_udp, im_tcp, and im_ssl) all set the $MessageSourceAddress
field, and this value will be used when sending the UDP datagrams (unless SpoofAddress is explicitly set to something else).
This allows logs to be collected over reliable and secure transports (like SSL), while the om_udpspoof module is only used for forwarding to the destination server that requires spoofed UDP input.
Configuration
The om_udpspoof module accepts the following directives in addition to the common module directives. The Host directive is required.
Required directives
The following directives are required for the module to start.
The module connects to this IP address or hostname. If using a hostname, the module resolves the hostname to an IP address on each new connection. You can define the port number by appending it to the IP address or hostname using a colon as a separator ( IPv6 addresses must be enclosed in square brackets ( You can define this directive multiple times to connect to multiple hosts or ports in failover mode. Specify IPv4 and IPv6 addresses separately as needed. If you use a DNS name, you should keep the addresses or CNAMEs below 16 to avoid issues caused by DNS response size limits.
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Optional directives
This optional directive specifies the local port number of the connection. If this is not specified, a random high port number will be used, which is not always ideal in firewalled network environments.
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This directive can be used to specify the maximum transfer size of the IP data fragments.
If this value exceeds the MTU size of the sending interface, an error may occur and the packet be dropped.
The default MTU value is |
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See the OutputType directive in the list of common module directives. If this directive is not specified, the default is Dgram. |
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This optional directive sets the reconnect interval in seconds. If it is set, the module attempts to reconnect in every defined second. If it is not set, the reconnect interval will start at 1 second and double with every attempt. In the latter case, when the system decides that the reconnection is successful, the reconnect interval is immediately reset to 1 sec.
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This optional directive defines the behavior when the connection with the remote host is lost.
When set to |
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This optional directive sets the socket buffer size (SO_SNDBUF) to the value specified. If this is not set, the operating system default is used. |
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The module rewrites the IP address depending on the value of this directive:
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Examples
The im_tcp module will accept log messages via TCP and will set the $MessageSourceAddress
field for each event.
This value will be used by om_udpspoof to set the UDP source address when sending the data to logserver via UDP.
<Input tcp>
Module im_tcp
ListenAddr 0.0.0.0:1514
</Input>
<Output udpspoof>
Module om_udpspoof
Host logserver.example.com:1514
</Output>
<Route tcp_to_udpspoof>
Path tcp => udpspoof
</Route>
This configuration accepts log messages via TCP and UDP and also reads logs from a file.
Both im_tcp and im_udp set the $MessageSourceAddress
field for incoming messages, and in both cases this is used to set $sourceaddr
.
The im_file module instance is configured to set the $sourceaddr
field to 10.1.2.3
for all log messages.
Finally, the om_udpspoof output module instance is configured to read the value of the $sourceaddr
field for spoofing the UDP source address.
<Input tcp>
Module im_tcp
ListenAddr 0.0.0.0:1514
Exec $sourceaddr = $MessageSourceAddress;
</Input>
<Input udp>
Module im_udp
ListenAddr 0.0.0.0:1514
Exec $sourceaddr = $MessageSourceAddress;
</Input>
<Input file>
Module im_file
File '/var/log/myapp.log'
Exec $sourceaddr = 10.1.2.3;
</Input>
<Output udpspoof>
Module om_udpspoof
Host 10.0.0.1:1514
SpoofAddress $sourceaddr
</Output>
<Route all_to_file>
Path tcp, udp, file => udpspoof
</Route>