Network Address Translation (NAT) presents significant challenges for battery-powered IoT devices aiming for low power consumption. Because devices behind NAT can't be directly addressed from the outside, they must maintain persistent outbound connections to receive data, negating the power-saving benefits of sleep modes. Techniques like keep-alive messages or frequent polling to maintain these connections consume significant energy. This post advocates for solutions that bypass NAT, such as IPv6 with its vast address space enabling globally routable unique addresses for each device, or by employing intermediaries like a message broker positioned outside the NAT. These approaches allow devices to initiate communication only when necessary, drastically reducing power consumption and extending battery life.
The blog post "NAT Is the Enemy of Low Power Devices" on golioth.io elaborates on the significant challenges Network Address Translation (NAT) presents to Internet of Things (IoT) devices, particularly those operating under low-power constraints. The core argument revolves around the inherent incompatibility between NAT's design, which assumes client-initiated connections, and the operational requirements of many battery-powered IoT devices that need to receive inbound data efficiently.
The author meticulously explains that conventional internet communication relies on devices having globally unique IP addresses. NAT, commonly implemented in home and enterprise networks, allows multiple devices to share a single public IP address, conserving the limited pool of IPv4 addresses. This is achieved by mapping internal private IP addresses to the public IP address and maintaining a translation table to route incoming traffic correctly. However, this mechanism typically requires the internal device to initiate an outbound connection first, establishing a mapping entry in the NAT table, before external services can reach it.
This poses a serious problem for low-power devices, as maintaining an active connection for inbound data consumes considerable energy. Keeping the radio active and regularly sending "keep-alive" messages to maintain the NAT mapping defeats the purpose of power-saving sleep modes. The article highlights the trade-off between responsiveness and battery life, forcing developers to choose between promptly receiving data and extending battery longevity.
The blog post further explores the difficulties in implementing workarounds like port forwarding and hole punching. Port forwarding, while a viable solution, requires manual configuration on the router and exposes security vulnerabilities. Hole punching, a technique involving both the device and a server connecting to a third-party rendezvous server to establish a direct connection, is described as complex and unreliable, especially behind symmetric NATs.
As a potential solution, the article advocates for protocols specifically designed for constrained devices, such as CoAP and MQTT, which operate over UDP and offer features like publish-subscribe messaging, reducing the need for constant connections. These protocols, combined with cloud services designed for IoT, can bypass the limitations of NAT by leveraging always-on cloud servers as intermediaries. The server maintains a persistent connection, acting as a bridge between external services and the low-power device, relaying messages efficiently while allowing the device to remain in a low-power state. In conclusion, the author emphasizes that addressing the NAT problem is crucial for the widespread adoption and efficient operation of low-power IoT devices, urging for greater consideration of NAT's implications in the design and deployment of such devices.
Summary of Comments ( 83 )
https://news.ycombinator.com/item?id=43003999
Several commenters on Hacker News discussed the challenges of NAT traversal for low-power devices, agreeing with the article's premise. Some suggested solutions like using a TURN server or a lightweight VPN, while others pointed out the benefits of IPv6 in eliminating the need for NAT entirely. One commenter highlighted the trade-offs between power consumption and complexity when implementing these workarounds, and another mentioned the difficulty of managing NAT keepalives with devices that sleep frequently. The issue of scaling these solutions for a large number of devices was also raised. Several users shared personal anecdotes of struggling with similar NAT issues. One commenter proposed a simpler approach involving a central server that all devices could communicate with, bypassing direct peer-to-peer communication and thus avoiding NAT complications altogether.
The Hacker News post "NAT Is the Enemy of Low Power Devices" generated several comments discussing the challenges of Network Address Translation (NAT) for low-power, battery-operated IoT devices.
Several commenters agreed with the article's premise. One highlighted the inherent difficulty in establishing inbound connections to devices behind NAT, emphasizing the power consumption overhead associated with maintaining persistent connections or using techniques like keep-alives. They also mentioned the complexities introduced by Carrier-grade NAT (CGNAT), where multiple layers of NAT further complicate inbound connections.
Another commenter pointed out the security implications of opening ports on a home router for these devices, suggesting that it exposes the entire local network to potential vulnerabilities. They advocated for cloud-based solutions like the one offered by Golioth (the article's author), where devices initiate outbound connections to a central server, eliminating the need for inbound port forwarding.
The discussion also touched upon alternative approaches to circumvent NAT limitations. One commenter suggested using protocols designed for peer-to-peer communication, like WebRTC, which can establish connections even behind NAT. However, another commenter countered that WebRTC still requires a signaling server and might not be suitable for all low-power applications due to its relatively high overhead.
Some commenters questioned the framing of NAT as the "enemy." They argued that NAT is a crucial part of the current internet infrastructure and that the real challenge lies in developing efficient protocols and architectures for IoT devices that can work within the constraints of NAT. They proposed solutions like using UDP hole punching or having devices establish outgoing connections to a central server.
One commenter explored the specific challenges posed by CGNAT, noting the scarcity of IPv4 addresses and the consequent widespread deployment of CGNAT by internet service providers. They mentioned techniques like STUN (Session Traversal Utilities for NAT) and TURN (Traversal Using Relays around NAT) but acknowledged their limitations and complexity, particularly for low-power devices.
Finally, a few commenters mentioned specific technologies and protocols, like MQTT and CoAP, which are commonly used in IoT and are designed to be efficient in low-power and bandwidth-constrained environments. They discussed how these protocols can be used in conjunction with cloud-based services to overcome the challenges posed by NAT.