[Theme: Twenty Eleven] I want to display on index.php, only post a category….

[Theme: Twenty Eleven]
I want to display on index.php, only post a category.
Could someone help me?

<?php if ( have_posts() ) : ?>

        <?php twentyeleven_content_nav( 'nav-above' ); ?>

        <?php /* Start the Loop */ ?>
        <?php while ( have_posts() ) : the_post(); ?>

               <?php get_template_part( 'content', get_post_format() ); ?>

        <?php endwhile; ?>

               <?php twentyeleven_content_nav( 'nav-below' ); ?>

       <?php else : ?>

Includes before the first line <? Php if (have_posts ()):?> i includes:
<? php query_posts (“category_name = photos”);?>
Ok. Only posts in category “Photos” are displayed. But unlike when the index.php displays all the posts and paging (<? Php twentyeleven_content_nav (‘nav-above’);?>) Is perfect, when I pick up one category to the next page shows the same posts from the previous page, or That is, does not allow navigation between the pages of posts.

tks.

[edluso]