Buying your own cable modem: DOCSIS 3.1, 4.0 and ISP approved lists

The short version

• Buy from your provider's list, for your tier. Every cable provider we checked publishes which modems it allows, by model or by specification, and most split the rules by speed tier. A modem on the list for a slower tier can activate and still cap your plan.
• DOCSIS 3.1 is the practical minimum. Optimum and Sparklight require it, Mediacom's list names only high-split DOCSIS 3.1 modems, Cox lists DOCSIS 3.0 modems only up to its 500 Mbps tier, and none of the eight providers' pages we read lists a retail DOCSIS 4.0 modem.
• For plans above 1 Gbps, get a 2.5 Gbps Ethernet port. A gigabit port carries about 940 Mbps of data, so it caps a 1.2 or 2 Gbps plan. Cox, Astound and WOW say so outright, and Xfinity's own list rates gigabit-port models at 927 to 957 Mbps and 2.5 Gbps-port models at 2.32 to 2.37 Gbps.
• The main caveats: some tiers need the provider's equipment whatever you buy (the first check below), and so does most providers' phone service. Check both before you buy, and keep the receipt.

Four checks before you buy

1. Can you use your own modem on your plan at all? Xfinity says "customer-owned modems are not currently compatible with X-Class speeds", its equal-upload tiers. Spectrum says "Customer-owned modems are only authorized for non-symmetrical speed tiers." Astound's 5 Gig by 1 Gig tier needs Astound's modem because "there's no retail modem available yet that supports this speed". Fiber service doesn't use a cable modem: WOW, Sparklight and Astound require their own fiber terminal (ONT or ONU) in fiber areas.
2. Is the model on the list for your speed tier? See the provider table below. Spectrum's list stops at tiers "up to 1G"; it names no retail modem for its 2 Gig tier.
3. Does its Ethernet port match the plan? Anything above 1 Gbps needs a 2.5 Gbps port, and a router with a matching internet port.
4. Do you have the provider's phone service? If so, you usually keep renting its phone modem. Details in phone service below.

Whether buying pays off depends on what you pay now (Spectrum's modem is already free). Our guide to ISP equipment fees lists each provider's charge and the months a purchase takes to pay for itself.

DOCSIS 3.0, 3.1 and 4.0 in plain terms

DOCSIS (Data Over Cable Service Interface Specification) is the standard cable modems use, written by CableLabs, the cable industry's research consortium. Each generation raised what the network can carry. CableLabs' own summary, which it notes is "based on specifications; deployed network performance will vary across implementations":

Those are network capacities, shared by everyone on a node, not what one modem gets. CableLabs' description of typical modems is closer to what you buy:

• DOCSIS 3.0 bonds several standard channels together. A modem with 32 downstream and 4 upstream channels "could theoretically get a peak throughput of 1 Gbps/100 Mbps". Providers' lists describe these modems by channel count, such as 24x8 or 32x8 (downstream x upstream).
• DOCSIS 3.1 adds wide OFDM channels. A typical modem, with two OFDM channels plus 32 standard ones downstream, "theoretically would get to a throughput of 5 Gbps/1.7 Gbps". ARRIS lists a similar layout for its SURFboard S33 and S34, with more standard upstream channels: "2 downstream x 2 upstream OFDM" and "32 downstream x 8 upstream DOCSIS 3.0 bonded channels".
• Upload depends on the provider's plant, not just the modem. CableLabs gives DOCSIS 3.1 upstream ranges of 100 to 250 Mbps on a low-split plant, 250 to 575 Mbps on a mid-split plant and 1.5 to 1.7 Gbps on a high-split plant. That is why some lists separate modems for upgraded areas: Xfinity groups modems that "support 100 Mbps upload speeds and above in certain markets", and Mediacom requires "a high-split DOCSIS 3.1 certified modem or above".
• DOCSIS 3.1+ is CableLabs' name for 3.1 modems with four or five OFDM channels, which "will enable up to 8 or 9 Gbps on the downstream" where the network has the spectrum. CableLabs says such modems were certified in 2025.
• DOCSIS 4.0 modems have at least five OFDM downstream and seven OFDMA upstream channels. On a full-duplex network, CableLabs says one can reach "up to 6 Gbps on the upstream and 9-10 Gbps or more on the downstream" (4.2 to 6 Gbps upstream on the other, frequency-split design). Its February 2026 update says operators are deploying outside-plant parts first, then network equipment, "and ultimately the cable modems to the customer homes".

What that means for a buyer today: a DOCSIS 3.1 modem with a 2.5 Gbps port covers every retail-modem tier on the lists in this article, and no list includes a DOCSIS 4.0 model. CableLabs says DOCSIS networks are "designed with backward compatibility", but providers still set their own floor: Optimum says "we do not allow DOSCIS [sic] 2.0 or DOCSIS 3.0 modems", WOW won't allow additional DOCSIS 3.0 4x4 or 8x4 modems, and Cox's tables cap DOCSIS 3.0 modems at its 500 Mbps tier.

The Ethernet port is the real speed limit

A modem passes your plan to the router through an Ethernet port. A gigabit (1 Gbps) port carries about 940 Mbps of actual data after protocol overhead (the arithmetic); WOW's own guidelines say the same, that over a 1 Gbps Ethernet port the speed to a single wired device "WILL GENERALLY BE UP TO 940MBPS" (capitals in the original). A 2.5 Gbps port carries about 2.35 Gbps.

Providers' own documents show the same split:

• Xfinity's list gives a wired download figure for every model: 20 of the 36 are rated at gigabit-port figures of 927 to 957 Mbps, the 16 others at 2.32 to 2.37 Gbps. Several older Xfinity plans still on its broadband labels exceed a gigabit port: Gigabit at up to 1,100 Mbps, Gigabit Extra at 1,200 to 1,300 Mbps and Gigabit x2 at 2,100 Mbps.
• Spectrum's typical download for Internet 1 Gig is 1,045 Mbps, measured at the modem, per its broadband disclosure. A gigabit port can't deliver that figure to your router.
• Cox: "For speeds of 1 Gbps and above, the modem/gateway must have a minimum 2.5 Gbps ethernet port." Its pricing guide says the same for Go Super Fast (1 Gig).
• Astound: its equipment page says a "DOCSIS 3.1 modem with 2.5GE physical LAN port is required for 1 Gigabit speeds and higher"; its bring-your-own-modem page calls a 2.5GE port a recommendation "for speeds above 1000 Mbps".
• WOW: DOCSIS 3.1 is "Recommended" for 1,000 Mbps, and DOCSIS 3.1 "32 x 8 with 2.5GbE Port" is "Required" for 1,200 and 2,000 Mbps.

What each provider's list says

From each provider's own list and support pages, checked October 29, 2026. Lists change when providers upgrade their networks; check yours again on the day you buy.

Some details that change the answer:

• Lists differ on the same model. Sparklight recommends the Motorola MB8600; Astound says it "has known issues connecting to Astound's network". Spectrum's approved lists include no Motorola models, while Xfinity, Cox, Sparklight and Astound list the MB8611.
• Lists and rules can disagree inside one provider. Cox's 1 Gig list includes gigabit-port models such as the SB8200 and CM2500, while its disclosures require a 2.5 Gbps port "For speeds of 1 Gbps and above". Mediacom's list requires high-split DOCSIS 3.1, while its broadband disclosures still allow a modem "certified in DOCSIS 3.0 or 3.1". Follow the stricter rule.
• "Compatible" isn't "full speed". Spectrum warns that if you install a listed modem that "doesn't meet the speed tier you ordered", you'll get a message and must acknowledge it. Xfinity says owned devices "should work for service tier speeds available before the recent upgrade" in upgraded areas, which can mean a slower tier.
• Cox is mid-transition. If you're in a former Cox area, find out whether your plan is a legacy Cox plan (Cox's list) or a Spectrum plan (Spectrum's policy) before choosing a list.

Modems that appear on most lists

Buying a model that several providers approve makes it more likely to work if you move to another cable provider (it still has to be activated there). These are the models with 2.5 Gbps-class figures on Xfinity's list that also appear on at least two other lists, plus two common gigabit models for comparison:

Two notes. Check upload as well as download: Xfinity rates its recommended 2.5 Gbps models at 444 to 486 Mbps of wired upload. And on prices, of the makers' pages we read only NETGEAR's store lists one: $299.99 for the CM3000 and $249.99 for the CM2500 (checked October 29, 2026). The ARRIS SURFboard product pages we read show no price.

A modem with built-in Wi-Fi (a gateway, such as the G36) works too, but the Wi-Fi is then tied to the modem, and a router added behind it risks double NAT; a modem without Wi-Fi keeps the roles separate.

Phone service and other services that need the provider's box

Cable phone service runs through a modem with a built-in phone adapter, called an eMTA. Most providers won't let you supply one:

Some provider features also depend on the rented gateway rather than the modem: Xfinity says owned devices don't get "Xfinity-exclusive features like built-in Xfinity CyberSecure or network management tools in the Xfinity app", and Cox's Panoramic Wifi features need its gateway. Support changes too: Spectrum's technicians support "only Spectrum-provided equipment", Cox supports only modems bought or rented from Cox, and Optimum says purchased modems "don't include tech support".

Used modems, expiring certificates and old models

• Buy new. Cox says that if you bought or received a modem used, "it is possible the modem cannot be used with your Internet service", so contact it first. Sparklight lists reasons a second-hand modem may fail, including that it "may be stolen or belong to another Internet Service Provider", and notes you usually can't return a used modem that won't activate.
• Old modems can stop working. Xfinity says DOCSIS security certificates inside modems "have limited lifespans", and lists models that will lose service, or may lose it, when theirs expire; the "may" list includes several Motorola SB5100-series and SB6180/SB6182 units and the NETGEAR CMD31T. Sparklight keeps an "End of Life" category for once-approved models it no longer allows to register.
• The provider can slow an incompatible modem. Cox's disclosures say it "may reduce the download and/or upload speeds available to customers using incompatible modems" and will notify you how to restore service.

Activating it

The general order: connect the coax cable and power, wait for the modem's online light, connect your router's internet (WAN) port to the modem, then register the modem with the provider. Spectrum, WOW and Astound ask for its MAC address, printed on the modem's label. What each documents:

Then return the rented modem or gateway and keep the receipt; unreturned-equipment charges and return deadlines are in our equipment fee guide and move with your network. If you keep the provider's gateway instead, bridge mode is how your own router gets the connection.

Pairing a router with the modem

The router's internet (WAN) port has to match the modem's port, or it becomes the bottleneck: a 2.5 Gbps modem feeding a router with a gigabit internet port still delivers about 940 Mbps. Of the 101 current Wi-Fi routers and mesh systems in the RouterHaus catalog, 88 have a 2.5 Gbps or faster internet port (catalog checked October 20, 2026). For wired devices to see more than a gigabit, the router also needs a LAN port faster than 1 Gbps, which not every multi-gig router has (LAN ports and switches).

The table shows the four cheapest current indoor routers and mesh units in the catalog with 2.5 Gbps or faster internet and LAN ports and a confirmed maker price. One of them, the ASUS GT-AX6000, is also on Cox's own list of "2Gbps Capable Retail Routers", alongside the ASUS GT-AXE16000.

The table shows "Not published" for all four makers' routing figures, so a 2.5 Gbps port isn't proof the router can route a full 2 Gbps; see choosing a router for multi-gig fiber for what is published. For coverage, size the router to the home, not the plan: the network planner does both. For the wider picture of running your own equipment with each provider, see own your home network and the ISP independence hub.