By default, dynamic segments don't accept dots - this is because the dot is used as a separator for formatted routes. However, you can add some regex requirements to the route parameters. Here, you want to allow the dots in the parameters.
match 'some_action/:id' => 'controller#action', :constraints => { :id => /[0-z.]+/ }
And in rails 2.3:
map.connect 'some_action/:id', :controller => 'controller', :action => 'action', :requirements => { :id => /[0-z.]+/ }
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