I want to know what differs in the following two lines:
cache_peer cache.myparent.example parent 3128 3130 cache_peer cache.sibling.example sibling 3128 3130
For you reference, this says:
If you have to use your Internet Service Provider's cache, you will have to configure Squid to query that machine as a parent. Configuring their cache as a sibling would probably return error pages for every URL that they do not already have in their cache.