It is the cable type that matters - Cat5e and you could have whatever connectors you want on the end. RJ11, RJ12, RJ45, BT601, jack plug ...

Don't take the risk with the one you link to but the other as linked to by ukhardy07 - here will be ideal.

It may be RJ11 at both end but the critical part is Cat5e (and only the thinner 2 pair which is good). RJ11 will fit into an RJ45 - they were designed to do that, or contact the seller and ask if he will make an RJ11 to RJ45 one for you and at your required length.. All his cables are hand made in the UK

He also, for example does RJ11 to RJ45 in Cat6 LINK

And this is the one you may need:

https://www.ebay.co.uk/itm/BT-Infinity-5M-Cat-5e-Mod... And at £9.99 cheaper than the link you have.

Or, if the master has unfiltered connections on the back plate then connect a standard cat5e directly to those and at the other end fit an RJ45 socket and use a short cat5e drop lead to connect from that to the router. Saves having to worry about the plugs on either end of the extension at all.

I agree, a much better way, however, not always the cheapest and making the connections puts some people off.

And my earlier point about avoiding potential noise sources is still relevant.

Edited by MHC (Thu 29-Mar-18 10:17:01)

It just says DSL underneath it; it's a Frtiz!box 3490.

Don't DSL and WAN ports serve the same role though? (provide connection to the internet through your DSL, rather than to your local area network [LAN] )

My previous modems/router just used an RJ11-RJ11.

Thanks.

What do you mean by "only the thinner 2 pair which is good" ?

Cat5e cable can be either 4-pair or 2-pair. ADSL and VDSL only require a single pair and an RJ11 normally has just 4 pins populated wit two empty. 2-pair is thinner and easier to use than 4-pair.

If you try to terminate 4 pair in n RJ11 there will be two pairs that are just cut and bare at the end - they look untidy and are a waste as well as not being enough room for them to be inside the connector and gripped.

I make my own - and always use 2-pair Cat5e.

If you have a separate modem which interfaces to the VDSL then the output of that will go to the WAN port on the router - it is Ethernet not VDSL level signals.