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I see that most dedicated hosting providers provide 3-4 secondary IP Addresses for free.
I wish to know what are the possible benefits of these secondary IP Addresses.

One would be to host different domains on different IPs. Other might be if I need to setup my own DNS Server.

What else?

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primary and secondary dns server on the same box? not so good idea...

some possible usage:

  • multiple separate ftp sites. in ftp there is no concept of vhost unless you have couple of ips.
  • multiple separate https sites. for https each site requires separate ip
  • maybe virtualization and couple of completly independent servers running on the same platform.
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  • Presuming that FTP usernames are unique, don't you kind of have vhosts that way? i.e the FTP server serves the correct directory depending on the username you login with?
    – JamesHannah
    Jun 15, 2009 at 21:39
  • @JamesHannah well.. and what about situation when you provide service to couple of customers and all of them insist on having anonymous account. each of them separate one. sure you can add prefix with customer name to the user name but it's not always feasible.
    – pQd
    Jun 16, 2009 at 6:29
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If you are using https, you need an IP per website. The secure connection is formed before the webserver can see data, so the correct certificate is selected on the the basis of IP address (unless you have a wildcard cert for a single domain).

You might want to split services across the IP's so that you can control access with different firewalling or apply some sort of QoS rules.

You could assign services to different IP's to allow you to split those services to different machines easily, at a later date.

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  • On your last point, if I wish to add more machines and use my existing IPs, I would need to stay with the same hosting provider, right? I can't buy a machine from a separate provider and assign it my IPs from the current provider?
    – Sanjay
    Jun 20, 2009 at 18:46
  • Correct. The clients are working with domain names as a layer over the actual IP's which allows you to manage this kind of thing. Multiple IP's are mostly a tool for managing traffic or allowing mutiple copies of certain services to run on the same machine.
    – John McC
    Jun 22, 2009 at 0:47
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SSL requires one IP per vhost with older browsers, so having multiple IP addresses allows you to host multiple HTTPs sites.

Multiple IPs could also make traffic control easier depending on how you segregate DNS names/services between them. You could make it easier to move a service to another machine, or apply a ratelimit/firewall to just one IP.

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    That is not perfectly true, it is very well possible to host multiple SSL sites (even totally different domains) on a single port. You basically need to specify subjectAltName in the certifiacate to do that. There are some more field to correctly fill out but that is the most basic one to use..
    – Martin M.
    Jun 15, 2009 at 20:30
  • @Server Horror - can you point some tutorials / documentation ? it'll be interesting lecture. thanks.
    – pQd
    Jun 15, 2009 at 20:40
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    This might be ok if the sites are related. But if you host completely distinct sites on the same box, you really want to also seperate the SSL certificates. SNI (Server Name Indication) might be a possiblity for hosting multiple HTTPS sites on the same machine, though.
    – joschi
    Jun 15, 2009 at 20:40
  • @pQd: IIS6 can do multiple SSL sites on the same IP/port as per: microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/…. I haven't much current experience with Apache or anything else, but I'm sure there are equivalent HOWTOs to be found.
    – ThatGraemeGuy
    Jun 15, 2009 at 21:09
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    @pQd wiki.cacert.org/wiki/VhostTaskForce is a nice starting point
    – Martin M.
    Jun 15, 2009 at 21:13
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SSL/TLA and virtual hosts always used to be a problem. Chicken and egg problem, resulting in a one to one relationship between IP address and virtual host. This has now 'gone away' thanks to SNI, although it's still generally unknown. SNI is in a TLA extensions rfc from 6 years ago, but still isn't in widespread use.

There is a little bit of a write up on the gentoo wiki. Unfortunately due to lack of support with IE on XP and lack of support in IIS, it isn't going to get anywhere fast.

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In addition to the comments above, if you are running your own DNS servers you need 2 IPs for 2 nameservers, you can not share an IP with them.

The other IPs, as others have said, are good for hosting sites on a dedicated IP with SSL certificates.

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  • well.. in fact you can run dns server on one ip. not every domain reseller will accept such a config but it's doable. but what's the point of running two copies of dns server on same physical box? it's missing the point... there are free secondary dns services - it's much better to use one of those rather then get illusion of redundancy when you use two different ips bound to the same box.
    – pQd
    Jun 15, 2009 at 20:54
  • Totally agree with you - with regard to the illusion of redudancy. Much better to run 1 dns server, and use everydns.net as your backups with axfr.
    – Dave Drager
    Jun 16, 2009 at 12:22
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You can run a hypervisor and resell virtual machines with dedicated IPs, in addition to several other suggestions in this thread.

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