At first the problem: After the VegiKochbuch relaunch as Rails project I realized that all old links to recipes are broken and this causes a lot of 404 errors.
The old PHP link structure was: http://vegikochbuch.de/rezepte/rezept175.php
And now in Rails it’s: http://vegikochbuch.de/recipes/175
My solution was adding
match '/rezepte/rezept:id.php' => 'recipes#show'
It works and is realy simple. I don’t really know if this is the best way, but I like it!