Not just different IP, also it's recommended different C class IP, so as
@sashilover pointed out, different hosting is sometimes needed (not always, for example OVH have different C-class).
Personally, I don't believe in the full footprint idea.
There are reasonable things and unreasonable things
For example:
- Registrar: Namesilo have millions of domains. There is no manual review for this. In case you had a really good PBN with really good content, it won't even matter if blogs are in the same IP, because G would consider it the a real BN (not PBN)
- WHOIS: Nowadays, most registrars offer private WHOIS. Some people believe that going private with 100% of the domains is clearly a footprint. I don't believe so. Unless you use the exact same private mechanism for all the domains. This could only justify using different registrars (for using different whois private services). Personally I don't really believe that Google looks domains WHOIS at that level. At best non-private WHOIS
Remember that the footprint only makes Google flag your domains and send them to reviewers (meanwhile is true that it could outrank in SERPS for several months. When your domain (for example, a single site lets say:
yourpbndomain.com/method-to-buy-whatever) is under review (and consider that only pages with a high level of traction in terms of SERPs are flagged, because each review costs A LOT of $ to G), reviewers will only look at your content, not the footprint (the server and all that). So if you create decent quality content in your PBN (not spinned or shitty-translated), then it may pass the quality review system.
So essentially, a lot of people is over-obsessed with the PBN footprint. For a rule of thumb, my suggestion is: If you find REALLY good domains for a PBN, create a little ecosystem for them apart (their own quality hosting, their own registrar, their own everything, even their own non-private WHOIS), specially if you are going to fulfill them with really shit/thin content.
But for average PBN domains, just keep it simple. Follow a 80/20 rule: For 500 Domains, treat the top 100 domains with care, and the other 400 domains less carefully (unless you have spent $500 for each domain, then treat them all carefully!

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