Generating a traffic-summary file

To use this tool, you need either a traffic-summary file or a traffic-model file. To generate either of these files, you will need a packet capture of actual Samba activity on your network.

Use Wireshark to take a packet capture on your network of the traffic you want to generate. For example, if you want to simulate lots of users logging on, then take a capture at 8:30am when users are logging in.

Next, you need to convert your packet capture into a traffic summary file, using traffic_summary.pl. Basically this removes any sensitive information from the capture and summarizes what type of packet was sent and when.

Refer to the traffic_summary.pl --help help for more details, but the basic command will look something like:

tshark -r capture.pcapng -T pdml | traffic_summary.pl > traffic-summary.txt

Replaying a traffic-summary file

Once you have a traffic-summary file, you can use it to generate traffic. The traffic_replay tool gets passed the traffic-summary file, along with the full DNS hostname of the DC being tested. You also need to provide some user credentials, and possibly the Samba realm and workgroup (although the realm and workgroup may be determined automatically, for example from the /etc/smb.conf file, if one is present). E.g.

traffic_replay traffic-summary.txt my-dc.samdom.example.com -UAdmin%password -W samdom --realm=samdom.example.com --fixed-password=blahblah123!

This simply regenerates Samba activity seen in the traffic summary. The traffic is grouped into 'conversations' between a host and the DC. A user and machine account is created on the DC for each conversation, in order to allow logon and other operations to succeed. The script generates the same types of packets as those seen in the summary.

Creating users can be quite a time-consuming process, especially if a lot of conversations are being generated. To save time, the test users remain on the DC by default. You will need to run the --clean-up option to remove them, once you have finished generating traffic. Because the same test users are used across multiple runs of the tool, a consistent password for these users needs to be used - this is specified by the --fixed-password option.

The benefit of this tool over simply using tcprelay is that the traffic generated is independent of any specific network. No setup is needed beforehand on the test DC. The traffic no longer contains sensitive details, so the traffic summary could be potentially shared with other Samba developers.

However, replaying a traffic-summary directly is somewhat limited in what you can actually do. A more flexible approach is to generate the traffic using a model file.

Generating a traffic-model file

To create a traffic-model file, simply pass the traffic-summary file to the traffic_learner script. E.g.

traffic_learner traffic-summary.txt -o traffic-model.txt

This generates a model of the Samba activity in your network. This model-file can now be used to generate traffic.

Replaying the traffic-model file

Packet generation using a traffic-model file uses the same command as a traffic-summary file, e.g.

traffic_replay traffic-model.txt my-dc.samdom.example.com -UAdmin%password

By default, this will generate 60 seconds worth of traffic based on the model. You can specify longer using the --duration parameter.

The traffic generated is an approximation of what was seen in the network capture. The traffic generation involves some randomness, so running the same command multiple times may result in slightly different traffic being generated (although you can avoid this, by specifying the --random-seed option).

As well as changing how long the model runs for, you can also change how many conversations get generated and how fast the traffic gets replayed. To roughly double the number of conversations that get replayed, use --scale-traffic=2 or to approximately halve the number use --scale-traffic=0.5. To approximately double how quickly the conversations get replayed, use --replay-rate=2, or to halve this use --replay-rate=0.5

For example, to generate approximately 10 times the amount of traffic seen over a two-minute period (based on the network capture), use:

traffic_replay traffic-model.txt my-dc.samdom.example.com -UAdmin%password --fixed-password=blahblah123! --scale-traffic=10 --duration=120

Scaling the number of users

The performance of a Samba DC running a small subset of test users will be different to a fully-populated Samba DC running in a network. As the number of users increases, the size of the DB increases, and a very large DB will perform worse than a smaller DB.

To increase the size of the Samba DB, this tool can also create extra users and groups. These extra users are basically 'filler' for the DB. They won't actually be used to generate traffic, but they may slow down authentication of the test users.

For example, to populate the DB with an extra 5000 users (note this will take a while), use the command:

traffic_replay my-dc.samdom.example.com -UAdmin%password --generate-users-only --fixed-password=blahblah123! --number-of-users=5000

You can also create groups and assign users to groups. The users can be randomly assigned to groups - this includes any extra users created as well as the users that map to conversations. Use either --average-groups-per-user or --group-memberships to specify how many group memberships should be assigned to the test users.

For example, to assign the users in the replayed conversations into 10 groups on average, use a command like:

traffic_replay traffic-model.txt my-dc.samdom.example.com -UAdmin%password --fixed-password=blahblah123! --generate-users-only --number-of-groups=25 --average-groups-per-user=10

The users created by the test will have names like STGU-0-xyz. The groups generated have names like STGG-0-xyz.