Here we are going to take old references from Matt Cutts because I think that it didn’t change
In the video below from 2010, Matt Cutts mentioned that a webmaster should not create a reciprocal link for every page but it should be done only for the important pages. It took the example of a newspaper who linked to a website and the website linking back to the article where the website was mentioned. This means that reciprocal linking is an accepted practice in Google’s eyes.
In the Google webmaster guidelines, some link exchanges are prohibited:
Excessive link exchanges (“Link to me and I’ll link to you”) or partner pages exclusively for the sake of cross-linking
The word “excessive” is very important here because that’s Matt Cutts who wanted the word excessive to be added. It means that there is perhaps a google penalty for those who overused reciprocal linking. I think about the situation where a website will add a footer link to a root domain B and that root domain B does the same in the mirror. I did this experiment on one of my websites, I have interlinked the 40 pages with 40 pages of another website. The links were in the sidebar and showed only on the page thanks to the wordpress plugin “widget logic”. This was a website about Hollywood actors. The two websites were complementary. One website page described the bio of an actor and the other page described the body measurement of an actor. Google juice benefited from each other and it was a success because those pages received more traffic than other pages.
In the following video, Matt Cutts mentioned that interlinking several websites
Surprisingly, there is another video about this. He mentioned once again that when you have three interlinked websites it is not a lot. This implies that there is a penalty when numerous websites have many reciprocal links.