A lot of ISPs including Sky, TalkTalk & BT don't use credentials set by the end user to authenticate users now, they use a Remote-ID that the wholesale provider injects into the PPP or DHCP requests to identify the line.

For FTTC this is done by the DSLAM and for FTTP it is done by the OLT.

In the case of DHCP this is done via Option 61 and for DHCPv6 via Options 18 and 37.

In Sky's case a plain DHCP or DHCPv6 request will work, no credentials need to be set on the customer router now (there are a couple of exceptions on old wholesale kit). TT are the same with DHCP. This is why in another thread a Sky user who got incorrectly patched to TalkTalk line connected OK to TT with their Sky router.

On PPPoE it works in a similar way with the Remote-ID being added to the PPPoE discovery packets.

Sky have some products that use PPPoE and as shown here it appears that a normal user can connect to their BNGs with PPPoE even if the official approach is DHCP.

In reply to a post by Ad_G:

A lot of ISPs including Sky, TalkTalk & BT don't use credentials set by the end user to authenticate users now, they use a Remote-ID that the wholesale provider injects into the PPP or DHCP requests to identify the line.

Thanks. Found a useful video that explains in a lot more detail, around 13 mins into the video.

https://youtu.be/03cwFIPdgQ8?t=786

To me the most obvious explanation is the router is trying both methods of connecting.

In reply to a post by Chrysalis:

To me the most obvious explanation is the router is trying both methods of connecting.

Nope, not the router, Sky accepting PPPoE, as per log I sent on previous post, and explained here:
https://forums.thinkbroadband.com/fibre/t/4781999-re...