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Openreach broadband providers

Many UK home ADSL Internet contracts are now sold by providers using the Openreach (ex-BT) infrastructure.

The following notes are from my experience; your mileage may vary, and no warranty is implied.

Sky

We used them from mid-2016 to mid-2018
They used both IPv6 and IPv4
Our Raspberry Pi did work as a home server with Dynamic DNS when configured to use IPv4-only (i.e. we had a public IPv4 address not suppressed by carrier-grade NAT)
The supplied router had both UPnP and DMZ options for setting up servers, and can reserve DHCP IPs for specific MAC addresses (useful for setting up wireless printers etc)
We did not understand Sky’s procedure for returning the router for recycling at the end of our contract, so we kept it (see below)
The ISP traffic management included the blocking of outgoing SYN packets when the uplink is loaded—so if a large upload is in progress, you won’t be able to create new connections but can use established SSH tunnels.
It’s a good idea to rate-limit large uploads on the client side anyway, so as to avoid completely saturating the uplink for other users in the home; the uplink is typically about 10 times slower than the downlink. You can ‘throttle’ some uploads with e.g. pv -L 64k < source | ssh server 'cat > dest'
Sky offered us a large introductory discount for 2016/17 (with no installation fee for the new line), then when we asked to leave at the end of the discounted period, they offered a smaller discount for 2017/18. But the discount they offered us for 2018/19 was smaller still, and switching became noticeably cheaper.

TalkTalk

We used them from mid-2018 to mid-2019
They used IPv4
Our Raspberry Pi worked as a home server (not suppressed by carrier-grade NAT)
TalkTalk’s supplied router was vulnerable to CVE-2018-8898 and we didn’t use it. But the procedure for returning it for recycling at the end of the contract was very straightforward—they automatically sent packaging and a label for us to take to a Post Office.
Sky’s router worked with TalkTalk after a simple restart; the only minor issue was its clock was stuck in 1970 because it came ‘hardwired’ to use Sky’s internal NTP servers on startup and these were not available via TalkTalk.
TalkTalk’s customer database system was slightly annoying: during sign-up they wrote down my name wrongly, and then they weren’t willing to fix it unless I submitted a certificate of Deed Poll or something (until I pointed out at the end of the contract that they were sending multiple “please renew at a smaller discount” letters with the wrongly-written name—evidently the customer-retentions team had the authority to fix it)
and when we left, the synchronisation of our switch date to the end of the discounted contract didn’t quite work and we had to pay a couple of pounds “early exit fee” for being off by a few days
They also seemed to get a bit confused by our attempt to give notice to leave. It turns out that if you want to change from one Openreach provider to another at the end of your contract, this is internally called a “working line takeover” and is not to be confused with cancelling the line altogether. So be sure to use the words “working line takeover” when talking about switching.

Post Office Broadband

We used them starting in mid-2019
In March 2021 they passed the business to Shell Energy but still with Post Office branding
They used IPv4 (and shared some infrastructure with Talktalk). Our IP address was changed on average 4 times each week, with a few minutes’ outage each time; changes were more frequent when our usage was high. (Geolocation services mapped these addresses to various towns in East Anglia; I *don’t* recommend submitting updates unless you can cope with potential vigilantes thinking they’ve “tracked down” future users of each IP to your location—you might be OK if it’s a large block of flats.)
Sky’s router did *not* work with GPO’s service (the latter required a login, which can reportedly be extracted from GPO’s router but cannot then be added in to Sky’s without serious reflashing)
but GPO’s own router (a modified AMG1302-T11C) had all necessary UPnP, DMZ, IP-reservation functions etc: we were able to copy over all configuration from Sky’s router, so no change was required on our client devices
Despite being shipped in 2019, the router had no support for the 2018 “WPA3” standard, and its “WPA2” is apparently a WPA1/WPA2 mixed mode, the security of which had been broken (but we weren’t worried with TLS/SSH on top)
GPO’s router had a poor WPS implementation: once you add a device (like a wireless printer) via WPS, all non-WPS devices are thrown off the WiFi until you restart the router, whereupon the WPS devices are locked out. So it’s best to leave WPS disabled: use “WiFi Direct” (Simple AP) to access the new device’s HTTP server and go from there.
Our Raspberry Pi worked as a home server (not suppressed by carrier-grade NAT), but all incoming connections appeared to originate at our home’s external IP address instead of the true outside address (it seems GPO’s router did NAT in *both* directions)—this made server diagnostics (and IP-related rules) more difficult, as none of the logs said where outside connections really came from other than “outside”.
GPO’s DNS server returned proxy addresses in Talktalk/Opal’s 62.24.128.0/17 block for some hosts, including github.com (interfering with SSH-based Git cloning), ssh.st0rage.org (interfering with SSH logins), and from late 2021 tilde.pink (interfering with Gemini protocol experiments). This could sometimes be worked around by setting .ssh/config to use alternate hosts (e.g. st0rage.org instead of ssh.st0rage.org, and ssh.github.com instead of github.com); it could also be worked around by using a public DNS server, or put the IP address into .ssh/config or /etc/hosts although this can change so you’ll have to keep it updated. On Android, Termux’s host command uses 8.8.8.8 but the Gemini clients don’t, so you’d need to use mobile data instead of WiFi to access tilde.pink on that platform.
GPO’s contract came with anytime landline calls to other Post Office Home Phone customers, and it was possible to share a referral bonus with one when signing up by telephone. But calls were *not* inclusive in *both* directions: only new customers starting after the end of January 2019 received the anytime inclusive calls to other Post Office numbers; they were *not* automatically granted for customers who’d started their contracts earlier. This led to a minor “bill shock” incident after we mistakenly told a relative that calls between us would be free in either direction.
The inclusive calls must not exceed one hour per call or they start billing extra.
The subset of customers who could make these inclusive calls continued to be able to do so after the Shell takeover in March 2021. We did not test if other customers were retrospectively added as a result of that takeover or not.
For renewal in 2020, we received a paper letter 2½ weeks before our end date, inviting us to log in to our account on their website and renew at the same discount given to new customers (unlike Sky and Talktalk who had offered us a smaller discount than their new customers). Confusingly, the renewal option was called “Upgrade” by the Web interface. GPO’s discounted price had increased by 13% for everyone (but that was still competitive as the whole industry had reduced their discounts), and they offered a 2-year price-fix for an additional 11%, which was worth it if and only if you expected the *following* year’s increase to exceed 22% (because they’d promised no mid-contract rises, making the basic contract a 1-year fix); although we hadn’t seen any publicity about ‘discount erosion’ from the press (which tended to write about *un*discounted prices) we still doubted GPO would think they could get away with a 22% hike one year after a 13% hike, so we went for the 1-year renewal. (As it turned out, the following year had no price increase at all.) We set the “go live” date to the first day after our original contract expired, which resulted in their system generating one un-discounted bill (it processed the billing a few hours before it processed the new contracts) but we were given credit for the overpayment.
For the 2021 renewal, the information offered beforehand did not confirm that the free calls to other Post Office numbers would still be included, but a call-centre operator said they would (and the letter sent immediately after listed these first)—but going via the call centre meant we were not controlling the “go live” date ourselves, and the operator set it 13 days too late, increasing one bill by a third.

Legal

All material © Silas S. Brown unless otherwise stated. Android is a trademark of Google LLC. CVE is a registered trademark of The MITRE Corporation. Git is a trademark of the Software Freedom Conservancy. Post Office is a registered trademark of Post Office Limited. Wi-Fi is a trademark of the Wi-Fi Alliance. Any other trademarks I mentioned without realising are trademarks of their respective holders.