I've recently been trying to resolve some issues with a 2926ac and remembered this old post which forum members helped me with. Mostly it was an issue around why Steve Gibson's very helpful 'Shield's Up' utility (at grc.com) was flagging a number of ports as being 'closed' rather than 'stealth'. Turns out it was our BB provider (Virgin Media) blocking them rather the router. Trees vs Wood. See tail end of this link: https://forums.whirlpool.net.au/archive/1526916