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Splunk Lantern

Total bytes out from source IP addresses

 

You want to create an accurate picture of outbound traffic on your network from each source IP address so that you can monitor for anomalous behavior. ​​​​

Data required 

Firewall data

Procedure

This sample search uses Fortinet FortiGate data. You can replace this source with any other firewall data used in your organization.

Run the following search. You can optimize it by specifying an index and adjusting the time range.

sourcetype=fgt_traffic src=<IP address sending the request> NOT (dest=<Internal IP address> OR dest=<DNS>) bytes_out>0
| eventstats sum(bytes_out) AS total_bytes_out BY src
| table src dest bytes_out total_bytes_out
| sort src – bytes_out

Search explanation

The table provides an explanation of what each part of this search achieves. You can adjust this query based on the specifics of your environment.

Splunk Search Explanation

sourcetype=fgt_traffic 

Search only Fortinet FortiGate network traffic data.

src=<IP address sending the request> 

Search data coming from this IP address.

If you want to search all IP addresses in a netblock, use a wildcard search. For example, src=192.168.255.*

NOT (dest=<Internal IP address> OR dest=<DNS>)

Exclude internal and DNS destination IP addresses.

Logs vary in the information they contain. Not all logs have hostnames or IP addresses. Sometimes the dest field will have a hostname in it but sometimes it will have an IP address. Parentheses and OR statements will broaden your search so you don’t miss anything. 

Example:
(dest=”192.0.2.0” OR dest_ip=”192.0.2.0”)

Example:
(dest=”192.0.2.0” OR dest=”example.com”)

bytes_out>0

Exclude results that do not have any outgoing traffic.

| eventstats sum(bytes_out) AS total_bytes_out BY src

Calculate the total volume of bytes_out to any destination for each source and display in a total_bytes_out column.

| table src dest bytes_out total_bytes_out

Display the results in a table with columns in the order shown.

| sort src – bytes_out

Sort the results by source with the lowest IP address first, and then by bytes_out with the largest volume of bytes_out for each source first.

Next steps

Use the results to establish baselines for each source IP address. You may want to investigate any destination that receives an unusually high amount of traffic from the overall bytes_out of a source. Adding on to your search to show percentages can help you determine more quickly whether there are IP addresses you want to investigate.

You might also be interested in other processes associated with the Monitoring for network traffic outliers use case.