Summary

  • The exchange's homepage states five port classes; multiplied by their nominal line rates they total 28,434 Gbps, which reproduces the printed "28+ terabits of connected member capacity" exactly. The printed total is therefore an inventory sum, not a measurement of provisioned or carrying capacity.
  • The same page prints "3.70 Tbps of peak traffic" and states no basis for it. The only ratio a reader can compute between the two figures is 13.0%, and that ratio is not utilisation: it divides an aggregate rate whose measurement the page does not describe by the sum of every member-facing port's line rate.
  • The operator's only published statement of what binds a participant delegates it to "the rules of the exchange", and its statement of price points at a join page that returned no readable text in the same review window.

The block itself

The page opens by describing the operator in its own words: "The SIX is a non-profit Internet Exchange Point in Seattle, Washington", offering "reliable and low-cost interconnection between member networks in the Northwest United States and beyond", with networks connecting "at speeds from 1 to Nx400 Gbps" (SIX homepage). Those are characterisations, and this briefing treats them as the operator's characterisations rather than as findings. The same page carries a block headed "Quick Facts", and that block is the whole quantitative record this review could read (SIX homepage). It prints: 372 ASNs, 442 routers, 371 members; then 14 member-facing 400GbE ports, 210 member-facing 100GbE ports, 1 member-facing 40GbE port, 178 member-facing 10GbE ports, 14 member-facing GigE ports; then 3.70 Tbps of peak traffic and 28+ terabits of connected member capacity.

Five port classes, five counts, two headline figures. Everything below is derived from that block and nothing else, and the derivation is shown in full so a reader can repeat or dispute it.

Why the capacity total closes

Take the counts at their printed speeds. Fourteen ports at 400 Gbps is 5,600 Gbps. Two hundred and ten at 100 Gbps is 21,000. One at 40 Gbps is 40. One hundred and seventy-eight at 10 Gbps is 1,780. Fourteen at 1 Gbps is 14. The sum is 28,434 Gbps, or 28.434 Tbps, and the port counts add to 417. The page's printed "28+" is therefore not an estimate, a rounded measurement or a range midpoint: it is the exact sum of the inventory it sits beneath, rounded down for display.

That closure is useful and it is also misleading, in a specific way. A figure that reconciles perfectly looks verified. Here the reconciliation proves one thing only: the publisher multiplied each port class by its nominal line rate and added the results correctly. It does not establish that any of the 417 ports is provisioned, that any is carrying traffic, or that the line rate on a given port is usable in full. The word "connected" in the printed label is doing work the arithmetic cannot support.

Publication is not operational reality; a nameplate sum becomes a statement about a network only when the ports behind it are up and loaded, and that step is not in this block.

The internal composition is worth stating for the same reason. The 14 ports at 400GbE plus the 210 at 100GbE are 224 ports, 53.7% of the printed inventory, and they account for 26,600 of the 28,434 Gbps, or 93.6% of the summed line rate. Four hundred and seventeen ports across 371 printed members is 1.12 ports per member. So the total is dominated by a little over half the ports, and the average member holds barely more than one.

One inconsistency in the same block should be recorded rather than resolved: the ASN count is 372 and the member count is 371. The page does not explain the difference, and this review will not invent one — an extra ASN can plausibly be an operator's own, a route server, or a stale entry, and choosing among those would be speculation (SIX homepage).

Why 13.0% is not utilisation

Dividing 3.70 Tbps by 28.434 Tbps gives 13.0%, and that number will travel. It should not travel as utilisation. The numerator is a peak rate whose measurement basis, window and aggregation unit the page does not state. The denominator is a sum of nominal line rates across every member-facing port. A sampled aggregate rate divided by a provisioning inventory is a comparison between two different objects, and the result is an artefact of their juxtaposition rather than a published statistic.

At the printed peak, the same two figures also give 8.87 Gbps averaged across the 417 ports and 9.97 Gbps averaged across the 371 members — averages over an inventory, not readings from any member's port.

What the operator does publish about measurement is a cadence, not a method. Its statistics page states that "the charts on this page are based on the IX standard 5 minute sampling rate", with a second page at one-minute resolution (SIX statistics page). That fixes how often a value is taken. It does not say what is summed, over which interfaces, or whether the headline 3.70 Tbps is a five-minute peak, a daily maximum or something else. A reader who wants utilisation needs the second thing and has been given the first.

The participant record is partly someone else's

The exchange publishes a participant table, and the page states both that the table is exportable — "CSV | Euro-IX JSON | PCH | SIX JSON | TSV" — and that "Some data is from PeeringDB.com and is updated hourly" (SIX participants page). That is unusually candid provenance, and it matters for anyone who intends to count members: part of the membership record is refreshed from a third-party database on an hourly cycle, which makes the roster a live feed rather than a fixed publication. It is a provenance statement about the list. It is not a traffic measurement, and it does not reconcile the ASN and member counts on the homepage.

What the operator says binds a member

The most consequential sentence in the retained set is not a number. The about page states: "There are no requirements of participants, other than they follow the rules of the exchange. There are no peering requirements, although peering with other members is encouraged and is basically the point of connecting to the exchange. We offer optional route servers." (SIX about page).

Read carefully, that sentence imposes nothing directly and transfers everything. The substantive obligation — what a participant must do, must not do, and what happens when it does not — lives in "the rules of the exchange". The same page disclaims peering requirements and describes route servers as optional, which narrows the field to that one instrument. This is a delegation, and the delegation is the finding: the operator tells a prospective member that the only thing binding them is a document it has not placed in front of the reader.

The price sits one sentence earlier: "One-time port fees are detailed on our join page. The SIX does not charge recurring fees, but they are offered as a payment option." (SIX about page). So there is a one-time charge, there is no mandatory recurring charge, and the amount is elsewhere.

The instrument that returned nothing

That join page returned no readable text in the same window (SIX join page). So did the paths the exchange uses for fees, port fees, technical requirements and membership. Five attempted locations, no readable page text, within two seconds of each other on 19 October 2026. This briefing cannot say why: an access restriction, a broken path and genuinely absent content all produce the same result from here. What can be said is narrower and still material. The one document class that would convert "no requirements other than the rules" into a checkable obligation, and the one document class that would convert "one-time port fees" into a price, were both unread in this review. The fee amount, the term, any notice procedure and the content of the rules are therefore unknown here — unknown, not absent, and not inferred.

The redundancy layer has the same shape. The route-server page says the service "is intended to supplement, not replace your direct peering" and tells participants that "it is important to establish sessions with all of the route servers available on the VLANs to which you are attached, so that maintenance on one route server does not affect your connectivity" (SIX route-server page). That is sound operational advice and it is addressed to members. It is not an operator commitment about availability, and no page in the retained set states one, or a service-level figure, or a credit remedy.

What would change this reading

A published methodology for the peak — window, interfaces, aggregation — would let the peak be compared with something. A readable fee schedule with a stated term and change procedure would turn a price into a term. A readable set of exchange rules would dissolve the delegation into specific obligations. A statement of how many of the 417 ports are provisioned would turn an inventory into a capacity claim. None of those was obtained. The directory record for the exchange is at the BTW directory entry for Seattle Internet Exchange.

A fuller picture of the exchange's public identity, its regional position and the prior discrepancy between registry, operator and aggregator records was published separately on 17 October 2026. This briefing deliberately does not re-measure that discrepancy. It takes the operator's own page as the object and asks a narrower question: which of these numbers can a reader check, and which merely look checkable.