First of all: I am well aware that in general it is a very bad idea to mix yum repos for different major OS versions.However on CentOS 7 I need a few packages from CentOS 6. So I have added CentOS 6 repos, replacing the $releasever with an explicit 6.8 (again, very bad, I know).Executing  yum list foobarI would expect to get a list of all available versions of foobar, from CentOS 7 AND 6. However yum only shows me el7 packages. I have verified that foobar is in the enabled CentOS 6 repo.I would have expected to be able to download/install a CentOS 6 package with something like the following, which fails:# yum --disablerepo=* --enablerepo=CentOS-6* install foobarLoaded plugins: fastestmirrorLoading mirror speeds from cached hostfileThere are no enabled repos. Run yum repolist all to see the repos you have. You can enable repos with yum-config-manager --enable <repo>Checking the repos as suggested:# yum repolist all |grep CentOS-6.8 - Basebase_6/x86_64                   CentOS-6.8 - Base                 enabled: 6,696Is yum doing an explicit check that the repo fits the major version? Or am I missing something else? 
Mixing yum repos for different OS major versions does not work
centos;yum;repository