Operator features

For Operators measuring within their own networks, and for the Server administrators who give them Operator Keys.

Operator Keys

An Operator Key is a Shared Key that the Server’s Key Table marks as belonging to an Operator. The Server decides: a Test gets an Operator’s allowances only when its Setup Request verified with a row marked operator = true, whatever the Client claims.

On the Server, in a TOML Key Table (Key files):

[[key]]
admin_key_name = "noc"
key_id = 200
key_hex = "c3d2e1f00f1e2d3c4b5a69788796a5b4c3d2e1f00f1e2d3c4b5a69788796a5b4"
operator = true
max_test_interval = 3600

max_test_interval is optional: without it, an Operator Key’s Tests are limited to 60 s like everyone else’s. An OB-UDPST udpst.keys file can’t mark Operator Keys.

On the Client, the key file needs only the key; operator there changes nothing:

[[key]]
admin_key_name = "noc"
key_id = 200
key_hex = "c3d2e1f00f1e2d3c4b5a69788796a5b4c3d2e1f00f1e2d3c4b5a69788796a5b4"

Give Operator Keys their own keyIds, and never share them with Consumers.

What an Operator Key allows

The last row matters only to Clients that set slowAdjThresh or trialInt, which the udpstp Client doesn’t.

An Operator Key is not exempt from authentication, tests_per_source (one Test at a time per Source by default), the Test Connection limits, the Admitted Rate Cap itself, require_max_bandwidth, or the Setup Request budgets.

Fixed-Rate Tests

A Fixed-Rate Test holds one Sending Rate Table row for its whole Test Interval instead of searching. Use it to check that a path carries a known rate, for example a provisioned service rate.

udpstp client --key-file noc.toml --fixed-rate 100 server.example.net

Rows 1 to 1000 offer that many Mbps at the IP layer; rows 1001 to 1152 offer the rates above 1 Gbps. Row 0 offers about 0.1 Mbps. The results’ header names the Test type:

Results
  Downstream Fixed-Rate Test with 127.0.0.1:24701, started 2026-09-26T14:50:11Z (T0)

A Test with an ordinary key is refused:

udpstp: the Server rejected the Activation Request; only an Operator Key may run a Fixed-Rate Test (RFC 9946 §4.1), so check the key, or the Server's log

with exit status 152; the Server logs reason="FixedRateNeedsOperatorKey". --fixed-rate and --start-row can’t be combined.

Check the IP-Layer Sender Bit Rate. A Fixed-Rate Test sends only as fast as the Load Sender can. Compare the B column, the Sender Bit Rate, with the row’s rate. When it is below the row’s rate, the host, not the path, set the result, and the Server’s log shows BurstsSkipped.

Long Test Intervals

An Operator Key with max_test_interval allows Tests longer than 60 s, up to that many seconds:

udpstp client --key-file noc.toml --test-interval 900 --delay-var rtt server.example.net

Above 60 s the Server judges by round-trip delay variation instead of one-way delay variation, which clock drift would distort over a long Test. Ask for it with --delay-var rtt; otherwise the Server coerces it and the Client says so:

The Server set useOwDelVar to 0 (asked for 1)

A Test Interval beyond the key’s maximum is coerced to it. Add --refuse-coercion testIntTime to have the Client end the Test instead (exit status 201).

MaxHops

MaxHops, the TTL or IPv6 hop limit of test traffic, keeps a Test’s load from straying beyond the path you mean to measure (RFC 9946 §10). Each end sets its own: the Server with max_hops, which RFC 9946 says the operator MUST set, and the Client with --max-hops (64 by default).

udpstp client --key-file noc.toml --max-hops 12 server.example.net

Set it a little above the number of hops on the path. Too small, and the load dies on the way: the Client reports “ICMP time-exceeded errors: –max-hops is too small for the path” instead of a low capacity, and the Server logs it.

DSCP

To measure a specific traffic class, mark the Test’s traffic with its DSCP:

udpstp client --key-file noc.toml --dscp 46 server.example.net

The Server allows a DSCP from its operator_allowed_dscp set for an Operator Key, and from allowed_dscp for anyone else. A DSCP outside the set is coerced to 0. The results’ parameters line says which DSCP was agreed, such as DSCP 46 agreed.

A Server administrator narrows the Operator set with, for example:

udpstp server --key-file keys.toml --max-hops 12 --operator-allowed-dscp 0,10,18,26,34,46

The ECN bits are always Not-ECT. Windows doesn’t let udpstp mark traffic (Platform differences).

Multi-Connection Tests at high rates

One Test Connection may not fill a multi-gigabit path. Spread the Test over several Test Connections, and over several Servers if one host can’t send enough:

udpstp client --key-file noc.toml --test-connections 8 --max-bandwidth 10000 server-a.example.net server-b.example.net

Running a Test explains the options, and Understanding the results how they are summed.