Well, to be more precise, which could be important in the future for the OP or any other reader, all equipment other than modems and modem/routers need filters.
The extension socket would also preferably have a DSL socket not a phone one.
If the OP might wish to use a phone on this extension in the future, fitting a filtered faceplate such as the XTF-68/85
or equivalent might be a neatness idea.
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