Game over for IPv4
Multi-user game players find it difficult to connect with peers if one player is behind a CGNAT gateway. Connection problems are easily resolved by using IPv6, but only if gaming technology developers actually support the modern protocol.
Large-scale deployment of CGNAT to squeeze a little more life out of IPv4 creates particular problems for peer-to-peer applications, such as multi-user games and internet/video telephony. With CGNAT, internet users are not directly contactable from the internet, even by port forwarding. As a result, it isn't possible to establish connections for direct real-time data exchange. Meaning that multi-user games won't work properly, and that audio and video connections only support one-way traffic, for example. Sometimes it's possible to get around such issues using STUN/TURN/ICE, but often there's no workaround. Where IPv6 is used, such problems simply don't arise, because everyone – every device – has a unique, fully routable address block. However, the benefits of IPv6 are obviously available to gamers only if game and console developers support IPv6.
Late last year, NIC.br, the Brazilian registry for the .br domain, surveyed its registrars to investigate the problems faced by gamers. Of the 172 respondents, 90 per cent reported that their customers did encounter gaming problems, even though more than half of the respondents already supported IPv6. "We did the survey because we've seen a recent upturn in service providers contacting us about gaming issues," explains Antonio Moreiras, internet specialist and project manager at NIC.br. "They wanted our help because they were getting complaints from customers unable to play online games due to connection problems. The registrars involved were using both CGNAT and IPv6. So it was apparent to us that some gaming platforms can't really work with either technology."
Seven thousand internet access providers
Brazil has a rapidly expanding internet market, on which a lot of young, small-scale ISPs are active. "This country has more than 5,500 cities," continues Moreiras, "and fewer than 10 per cent of them are covered by the big operators. The rest are served by small, regional access providers, who together account for a quarter of the market. As a result, we have more than six thousand autonomous systems (ASs), and upward of seven thousand internet access providers. Of those, 70 per cent have fewer than a thousand customers. And, to be honest, not all the smaller providers have the technical knowledge you would ideally want." With the LACNIC RIR having allocated the last regular IPv4 block in June 2014, many Latin American ISPs are unable to obtain more IPv4 addresses and lack the financial muscle to buy them in. "The public IPv4 addresses that they have are generally reserved for business customers," Moreiras previously told the Internet Governance Forum (IGF) 2018 (video). "Nearly all ordinary users are behind CGNAT gateways. Consequently, if one IPv4 address is blocked, that can sometimes mean that an ISP's entire network is unreachable." Many of the internet professionals attending the Forum had stories of fanatical gamers doing things such as ordering DDoS attacks to frustrate their opponents. Such behaviour makes the ISPs involved extremely vulnerable. NIC.br's survey also showed that some online games were using up to a thousand ports per client. Therefore, if you reserve two thousand addresses per user, a single IPv4 address can support a maximum of thirty users. What's more, games appear to have difficulty distinguishing between sessions originating from the same front-end address.
According to Moreiras, every conceivable kind of problem crops up in the field:
gaming platform doesn't support NAT, because, for example:
It depends on inward connections
It can't distinguish between sessions originating from the same IPv4 address
Some IPv4 addresses in the ISP's NAT pool are blacklisted
The gaming platform doesn't support IPv6 either
The ISP's IPv6 or CGNAT-implementation is flawed
"Most of the complaints we receive relate to the Sony PlayStation," says Moreiras, "but we get them about Xbox, League of Legends, Tibia and Cabal Online as well." Sony doesn't yet support IPv6, which it refers to as a future technology, and fobs users off by telling them to contact their provider, who should give them an IPv4 address.
On that score, Microsoft seems to have a better approach: "Right from the first Xbox design, IPv6 was in the picture," Darrin Veit from Microsoft's Xbox network group told IGF 2018. Nevertheless, the rise of CGNAT has created connection problems. Games that have a pure client-server architecture and only need to connect to Microsoft's servers are fine. But applications that also or exclusively use peer-to-peer technology are liable to have difficulties. Veit says it's a common problem for their customers. Microsoft activated IPv6 for Party Chat (a chat application for gamers, similar to Mumble) at the end of 2016, and followed up by enabling it for various other applications hit by connection problems. A little over a year later, with roughly half of their users then using IPv6, Microsoft enabled IPv6 by default. For peer-to-peer connections, the IPv6 connection routine starts first, immediately followed by the IPv4 routine. The connection that's established first is the one that's used. If a peer-to-peer connection between two users can't be achieved at all, communication is via a relay server operated by Microsoft, but that obviously introduces a time lag. Communication is an important element of Microsoft's IPv6 strategy. The user receives a warning in the Xbox network settings if their client has (CG)NAT-related connection problems. If the user only has IPv4 available, they are advised to enable IPv6 as well. Microsoft is now working on IPv6 support in all Xbox applications.
Paperclips and tape
Moreiras would like to see access providers and gaming technology developers working together on the implementation of IPv6. "They have a shared interest in making it happen so as to create added value for their customers." The stumbling block is, of course, a mismatch in the way costs and benefits are spread. However, e-sports players already benefit from using IPv6. And the advantage is tempting enough to warrant switching service provider. But the incentive would be much greater if it weren't for the fact that most gaming platforms don't support IPv6. Until IPv6 becomes the norm, access providers and gaming technology developers should at least be exchanging information about the limitations of IPv4 and the problems associated with CGNAT. Moreiras emphasises that, while IPv4 remains more widely used, IPv6 is the current Internet Protocol and the version on which all development and innovation is based. "The internet is currently held together by paperclips and tape. Most internet access providers can't give their customers IPv4 addresses any more. So they're dependent on CGNAT. But the fact of the matter is that CGNAT is a makeshift solution."