title: TCP RTT check

integration_title: TCP RTT Check

kind: integration

newhlevel: true

The TCP RTT check reports on roundtrip times between the host the agent is running on and any host it is communicating with. This check is passive and will only report RTT times for packets being sent and received from outside the check. The check itself will not send any packets.

This check is only shipped in the 64-bit DEB and RPM Datadog Agent packages.

The check uses timestamps provided by the PCAP library to compute the time between any outgoing packet and the corresponding TCP acknowledgement. As such, PCAP must be installed and configured.

Debian-based systems should use one of the following:

$ sudo apt-get install libcap

$ sudo apt-get install libcap2-bin

Redhat-based systems should use one of these:

$ sudo yum install libcap

$ sudo yum install compat-libcap1

Finally, configure PCAP:

$ sudo setcap cap_net_raw+ep /opt/datadog-agent/bin/go-metro

Edit the ```go-metro.yaml``` file in your agent's ```conf.d``` directory. The following is an example file that will show the TCP RTT times for app.datadoghq.com and 192.168.0.22:

init_config:

snaplen: 512

idle_ttl: 300

exp_ttl: 60

statsd_ip: 127.0.0.1

statsd_port: 8125

log_to_file: true

log_level: info

instances:

- interface: eth0

tags:

- env:prod

ips:

- 45.33.125.153

hosts:

- app.datadoghq.com

To validate that the check is running correctly, you should see `system.net.tcp.rtt` metrics showing in the Datadog interface. Also, if you run `sudo /etc/init.d/datadog-agent status`, you should see something similar to the following:

● datadog-agent.service - "Datadog Agent"

Loaded: loaded (/lib/...datadog-agent.service; enabled; vendor preset: enabled)

Active: active (running) since Thu 2016-03-31 20:35:27 UTC; 42min ago

Process: 10016 ExecStop=/opt/.../supervisorctl -c /etc/dd-....conf shutdown (code=exited, status=0/SUCCESS)

Process: 10021 ExecStart=/opt/.../start_agent.sh (code=exited, status=0/SUCCESS)

Main PID: 10025 (supervisord)

CGroup: /system.slice/datadog-agent.service

├─10025 /opt/datadog-...python /opt/datadog-agent/bin/supervisord -c /etc/dd-agent/supervisor.conf

├─10043 /opt/datadog-...python /opt/datadog-agent/agent/dogstatsd.py --use-local-forwarder

├─10044 /opt/datadog-agent/bin/go-metro -cfg=/etc/dd-agent/conf.d/go-metro.yaml

├─10046 /opt/datadog-.../python /opt/datadog-agent/agent/ddagent.py

└─10047 /opt/datadog-.../python /opt/datadog-agent/agent/agent.py foreground --use-local-forwarder

If the TCP RTT check has started you should see something similar to the go-metro line above.

This is a passive check, so unless there are packets actively being sent to the hosts mentioned in the yaml file, the metrics will not be reported.

|TCP RTT Metrics|

|-----|-----|

|system.net.tcp.rtt|

|system.net.tcp.rtt.avg|

|system.net.tcp.rtt.jitter|

{:.table}