Are links between websites hosted on the same IP address less interesting?
In most cases, websites publishers host all their sites on the same server with a single IP address.
Being aware of the impact of links on SEO, it is therefore very tempting to make create multiple links between our different websites.
These links take then the shape of a self recommendation that should probably have less value that a complete external one.
Mutualized servers make possible to host lots of websites on a same server, it is very common to see several publishers sharing the same IP address. Not corrupted and perfectly legitimate links can therefore be issued.
An automatic penalty would then be unfair and irrelevant.
However, an other line of approach can enable to generate relevancy from IP addresses.
Most websites probably get links coming from different IP addresses. In that respect, a website with an overwhelming majority of links coming from a single IP address would become suspect.
The resulting good practice is therefore to obtain links from multiple IP addresses as it is supposed to happen naturally.