---
layout: "docs"
page_title: "Commands: RTT"
sidebar_current: "docs-commands-rtt"
description: |-
Command: serf rtt
The rtt command estimates the network round trip time between two nodes using
Serf's network coordinate model of the cluster. See the Network Coordinates
internals guide for more information on how these coordinates are computed.
While contacting nodes as part of its normal gossip protocol, Serf builds up a
set of network coordinates for all the nodes in the cluster. Agents cache these,
and once the coordinates for two nodes are known, it's possible to estimate the
network round trip time between them using a simple calculation.
Usage: serf rtt [options] node1 [node2]
At least one node name is required. If the second node name isn't given, it
is set to the agent's node name. Note that these are node names as known to
Serf as serf members would show, not IP addresses.
The list of available flags are:
-rpc-addr - Address to the RPC server of the agent you want to contact
to send this command. If this isn't specified, the command will contact
"127.0.0.1:7373" which is the default RPC address of a Serf agent. This option
can also be controlled using the SERF_RPC_ADDR environment variable.
-rpc-auth - Optional RPC auth token. If the agent is configured to use
an auth token, then this must be provided or the agent will refuse the
command. This option can also be controlled using the SERF_RPC_AUTH
environment variable.
If coordinates are available, the command will print the estimated round trip
time between the given nodes:
$ serf rtt n1 n2
Estimated n1 <-> n2 rtt: 0.610 ms
$ serf rtt n2 # Running from n1
Estimated n1 <-> n2 rtt: 0.610 ms