You can do directory submissions for different websites even if they are on the same IP. This is perfectly fine. The problem is that if one of the sites with the IP does black hat SEO (buying text links, having links in bad neighborhoods, etc) then the other sites on the same IP can get penalized as well. Additionally, if the sites are linking to each other, it might not count as much towards page rank.

in my opinion submitting directories in same site(same IP)give only one backlinks and also consider as its better to submit in different sites having different IPs

It is always preferred to have different ip addresses. However if you use white hat methods you will be ok and get top placement.

Just use whitehat tecniques and normal backlinking strategies and you should be fine

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