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While hosting new service these days, what would be best decision. IPv4 or IPv6 ?

If we decided to launch it on IPv4 address:

  1. How easy/difficult to get IPv4 address (considering they getting exhausted out soon)?
  2. Can it be ported easily to IPv6 in coming future?
  3. How can existing IPv6 users be able to communicate with it?

If we decide to launch it on IPv6 address:

  1. How can existing IPv4 users be able to communicate with it?
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    @user2284570 Large scale NAT breaks applications which require end-to-end connectivity, such as VoIP, multiplayer gaming, and some others I've forgotten about. Which is why Xbox Live actually provides IPv6 tunnels (via Teredo) to people who don't have native IPv6.
    – Michael Hampton
    Jan 8, 2015 at 16:44
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    Related: Should I use IPv6 only or both IPv4 and IPv6 in my web server?
    – Michael Hampton
    Jan 8, 2015 at 16:50
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    @user2284570 Have you considered moving to a more civilised ISP (or country!)?
    – Michael Hampton
    Jan 8, 2015 at 18:00
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    @PeterHorvath Many of our internet standards turned out be quiet inefficent (take http, that thingy with backwards compatibility spoiles most innovations) and your are not even guaranteed that people follow it (see browser compatibilty for html5 elements and CSS 3). IPv6 may be a bad standard (I don't know, I didn't read that much about this topic), but at least it solves some problems we're facing like IPv4 exhaustion and especially the run for static ips (and ignorant programmers like Notch and many others who do not accept domain names as identification for their servers).
    – Sebb
    Jan 9, 2015 at 20:35
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    @PeterHorvath: you are just plain wrong. In many regions (RIPE, APNIC, LACNIC) the main supply of IPv4 addresses has run out. I'm co-chair of the RIPE Address Policy WG, so I'll focus on this region. Here every LIR (usually an ISP) can get a single block of 1024 IPv4 addresses and that's it. If they need anything more they'll have to buy it on the market from another ISP. Those 1024 are just to let them do something on the IPv4 internet, but are not nearly enough. NAT, virtual hosting etc are common, but we still run out. What you are seeing are existing ISPs using up their final supplies...
    – Sander Steffann
    Jan 10, 2015 at 11:50

3 Answers 3

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IPv4 and IPv6 are separate protocols that don't talk to each other. You'll have to support both protocols for now.

Getting IPv4 addresses is getting more difficult and expensive, but you'll have to make your service available over it because not all users will have IPv6. On the other side there will be users who don't have full IPv4 anymore. They might have to share their IPv4 address with many others, they only have IPv6 and need a translation service to reach IPv4 services etc. For those users and for future users you want to offer your service over IPv6 so that they can reach it in the most optimal way.

And hopefully in the not-so-distant future everybody will have IPv6 and we can get rid of IPv4 and the hacks and costs required to keep it working.

One way you could start your new service is to build everything for IPv6-only and put a translator (SIIT-DC or reverse proxy) next to it to translate incoming requests over IPv4 to IPv6. You'll be able to handle both protocols for now, and it will also be easy to clean up and remove the obsolete IPv4 stuff later.

This strategy is especially useful if your service runs on a cluster of servers. The whole cluster can run IPv6-only and you need only one IPv4 address on your translator. It's easier to only have to maintain one protocol on the majority of your machines and requiring less IPv4 addresses can also save you money. That's why companies like Facebook are doing this as well.

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  • And of course this single protocol translator will become the biggest single point of failure you will have, so you have to buy at least two, and configure as a ha cluster which of course is easy unless you have no idea how to do it.. but as you will be big as Facebook, believe me, it is really easy at this scale.
    – kakaz
    Oct 15, 2018 at 15:41
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    @kakaz A translator like described can be implemented in a completely stateless fashion, which will make it trivial to replicate. Of course since sites of that size need load-balancing, they may as well integrate the translator with load-balancing. Of course since the connection from load balancer to backend use an IP tunnel the need to translate can go away since the outer packet can be IPv6 even if the inner packet is IPv4.
    – kasperd
    Oct 15, 2018 at 17:02
  • But you know what is single point of failure?
    – kakaz
    Oct 15, 2018 at 17:21
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Both of course. IPv4 will stay a long time, and it's way past time to start with IPv6.

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    IPv4 will stay a long time: Sure, I’ve seen reports that some providers started to distribute private addresses to their subscriber instead of public ones. In the same time they don’t provide IPV6 acess (prefer GCN over ipv6 access).
    – user2284570
    Jan 8, 2015 at 13:16
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    @user2284570: That started a long time ago. I got DS-Lite with my home cable internet 2 years ago, which is the default for many providers now. Luckily, I could convince them I needed full DS.
    – Sven
    Jan 8, 2015 at 13:16
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    No, this different, there is no IPV6 parts. But maybe I’m too localized, in France every subscribers (whether private or companies) still get public ipv4 addresses
    – user2284570
    Jan 8, 2015 at 13:22
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    @user2284570: This is absolutely depending on the provider. It's also not really relevant as the important bit still is that IPv4 is here to stay for a long time.
    – Sven
    Jan 8, 2015 at 13:23
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    @user2284570 I think that happened to me in like 2002-2003 or so.
    – user
    Jan 8, 2015 at 15:14
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While hosting new service these days, what would be best decision. IPv4 or IPv6 ?

Assuming this is a service intended for use over the public internet by clients on machines or networks outside your control you should support both.

How easy/difficult to get IPv4 address (considering they getting exhausted out soon)?

For individual addresses you generally rent them from your hosting provider, most providers still include one with each server, but some are starting to charge extra for it. As the market price of IPv4 addresses rises we can expect the rental fees charged by service providers to rise too.

If you need blocks to run your own network things get harder. There is a market in IP blocks but AIUI it's more like buying real eastate than buying servers. In Europe it's also possible to register as a LIR and get a "final allocation" from RIPE, the downside of that approach is the ongoing fees (fees for a LIR are much higher than for "provider-independent" allocations).

Update: RIPE's pool for "final allocations" is now exhausted too.

Can it be ported easily to IPv6 in coming future?

IPv6 addresses are bigger than IPv4 ones so anything that stores IPs in a fixed-size field (whether text or binary) is problematic. Similarly IPv6 addresses in text form use colons rather than dots so anything that stores IP addresses in a structured text format is potentially problematic.

It is almost certainly easier to support both from the start than to try and track down every place IP addresses are stored and processed after the fact.

How can existing IPv6 users be able to communicate with it?

Currently a large proportion of the Internet is v4 only, so providers have to provide some means for their clients to access v4 only resources. Increasingly as IPv4 addreses get more expensive and harder to obtain they will be looking for mechanisms that allow them to do this without giving each customer a dedicated public IPv4 address.

There are a variety of approaches to this, including conventional IPv4 NAT at the ISP level, DS-Lite which tunnels IPv4 packets to a special IPv4 NAT over IPv6 and NAT64 which translates IPv6 packets to IPv4 packets. All of them will come at a cost in performance, reliability and ability to trace abuse.

How can existing IPv4 users be able to communicate with it?

Unlike in the previous case this is mostly your problem. Some clients may use teredo but windows disables teredo by default when it detects a domain controller and most other operating systems didn't support it out of the box at all. Even when teredo is enabled it's not exactly the most reliable mechanism.

So if you want your service to work for the majority of Internet users you need to offer it on IPv4.

That doesn't necessarily mean your servers have to support IPv4 though. For example if you front with a CDN like Cloudflare or Akamai then the CDN can receive the traffic over IPv4 and forward it to you over IPv6. I am also aware of one hosting provider that offers a free reverse proxy service for this customers. I expect such things to become more common as the price of IPv4 addresses and the proportion of clients supporting IPv6 both rise.

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