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I just signed up with DreamHost VPS, and their sign-up process offered an unique IP address for an additional ~$4/mo.

I know what IP addresses are. Why would this uniqueness matter? Visitors are accessing my website via URL addresses anyway.

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Are you sure that you signed up for a VPS and not a shared host? – MDMarra Nov 30 '11 at 18:24
@MarkM Yes, I chose VPS. I don't think I need an unique IP address anyway, so I'm not motivated to investigate this further... – Šime Vidas Nov 30 '11 at 18:40
According to it seems that DreamHost VPS comes with 1 unique IP address; DreamHost Shared has an IP address available as a $4 upgrade (and on the VPS you can purchase additional unique IP addresses (beyond the one) if you wanted to say host multiple sites each with unique IP on the your VPS). – dr jimbob Dec 1 '11 at 5:09
up vote 32 down vote accepted

The big one is that you need a unique IP address for some SSL/TLS implementations. As pointed out in the comments, no version of IE on XP can do this, which is the biggest offender.

Also, if you have an application that needs to reference an IP instead of a DNS name, you'd need it since your shared host is likely configured to ignore requests to an IP.

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+1 I don't have enough rep to up-vote :) – Šime Vidas Nov 30 '11 at 18:11
What they probably mean is that it's a static address - on a VPS it should always be "unique" (unless they're doing some crazy NAT silliness), but it may not be predictable - which is a problem for services which rely on DNS mapping your name to a specific address. – Shane Madden Nov 30 '11 at 18:15
@ShaneMadden I would hope that you'd get a static IP from a VPS provider. I'm inclined to believe that the OP has shared hosting, which would explain this option. – MDMarra Nov 30 '11 at 18:18
If you go run through you'll see a lot of small slice VPS hosts. Many/most of them give variable IP addresses. A lot run their own nameservers to compensate. – Driftpeasant Nov 30 '11 at 18:29
@Driftpeasant The confusion is that variable/static and unique/shared are separate qualities. – TessellatingHeckler Nov 30 '11 at 18:43

Blacklists (SEO, mailings etc.) are often based on IP, so having unique IP will reduce propability that you will suffer for someone's other actions.

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Another benefit is being able to point multiple domain names at your static IP address in order to run multiple stand-alone websites that each resolve to their own folders.

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If you don't know that you need a unique IP address, then you probably don't need one.

Some protocols and applications require a specific IP address, but for the ones most frequently used these days, host name alone is often sufficient.

Obviously, in the background, this must resolve to an IP address, but not necessarily a unique or fixed address. As long as the server understands enough to route the query appropriately, all the services could share the same pool of IP addresses without issue.

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Just because he doesn't know wether he needs a unique IP right now doesn't mean he won't need a unique IP later. Someone as a web developer may already understand a need to have SSL on login page but not necessarily understand reason to purchase unique IP from hosting service. – ra170 Dec 1 '11 at 2:51

I agree with Bill. If you don't know you need it, don't get it. You can always add it later if you find you need an ssl certificate (like for processing credit cards).

As for the comments you may hear online about security of having your site on a unique IP so that you are not lumped in with spammers, for example, almost everyone in the world is on shared servers. Most hosting companies now are good at responding to spam issues and making sure they get rid of bad clients.

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