Trema( https://yasuhito.github.io/trema-book/ )のサイトを参考に6章までできたのですが、gitコマンドでclone( https://github.com/trema/patch_panel.git )して、bundle installをしたあとに実行してみるとhost関係の以下のようなエラーが発生します。

[root@localhost patch_panel]# ./bin/trema run ./lib/patch_panel.rb -c patch_panel.conf
RTNETLINK answers: File exists
/opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/shell_runner.rb:5:in `sh': sudo ip link add name patch_panel_1 type veth peer name host1 failed. (RuntimeError)
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/virtual_link.rb:99:in `add'
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/virtual_link.rb:67:in `run'
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/virtual_link.rb:15:in `each'
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/virtual_link.rb:15:in `each'
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/configuration.rb:44:in `block in run'
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/configuration.rb:43:in `each'
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/phut-0.7.5/lib/phut/configuration.rb:43:in `run'
    from /opt/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/trema-0.9.0/lib/trema/command.rb:110:in `block in start_phut'

環境はCentOS 7です。よろしくお願いします。