| Network Working Group | S. Kerr |
| Internet-Draft | Beijing Internet Institute |
| Intended status: Informational | July 8, 2016 |
| Expires: January 9, 2017 |
A DNS Manifesto
draft-shane-dns-manifesto-00
The DNS protocol has many things to fix or improve, but this is difficult to do because changing the protocol is very hard. This paper explores the good and bad features of the protocol, and calls for an effort too make the protocol flexible enough that it can evolve in the future.
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The DNS protocol has been stretched in ways far beyond the original architecture. It continues to be pushed further, but at the same time is limited by old design decisions.
It is time to consider fundamental changes to the protocol. These changes should:
The DNS has gotten many things right.
[ talk about how the DNS is an old, successful protocol ]
The DNS name space is straightforward: labels separated by dots. EXAMPLE.COM. IP6.ARPA. IETF.ORG. This simple abstraction is easily understood by people, but also forms the basis that allows:
The name space has a few decisions which might be different if it was created today (such as being case-insensitive, and being limited to ASCII alphanumeric symbols and dash), but it is basically great. Any future protocol/scheme should keep the namespace in current use with the DNS.
Both the separation of responsibility and the hierarchy in the name space allow DNS to be massively scalable on both an organizational and a technological basis. Further, those responsible for any given name can use as many or as few resources to service that name as necessary.
Each label in the DNS name space is unique. However, within each label the way the data is maintained and published is completely redundant. This is achieved by having a set of servers, any of which can answer queries about the label.
This redundancy applies for every point in DNS. There is no single point of failure in the system.
The DNS architecture allows various components to re-use information for a period of time. This caching is a key part of scaling, as it moves the server load closer to where the data is consumed.
Because of this caching and because of the use of several different sources in data publication, potentially operated by independent and collaborating entities, different places of the Internet may have slightly different views of the DNS at any given time. This "loose consistency" is an explicit trade-off of exact answers for performance, and is key to the scaling of DNS today.
A relatively late addition to the DNS are the DNS Security Extensions (DNSSEC). This adds an authentication system to the data published in DNS. It is independent of how the data is published or accessed, meaning that it can be authenticated at any and every step as needed.
While the details of DNSSEC are more complicated than they would be if designed today, the principle of securing the data itself is good.
Open standards and open source implementations of the DNS have allowed it to be ported to every system on the Internet. Vendors have been able to provide solutions in many different ways, while at the same time dedicated individuals or organizations can solve problems on their own.
This also provides a low barrier to entry, which given the basic infrastructure nature of DNS, allows for a low barrier of entrance to deployment of new Internet services.
The DNS has a lot of cruft, which is not surprising for a technology more than 30 years old that has been changed every few months in that time.
The reason that this Manifesto is needed is at least partially because the DNS protocol itself is difficult to change.
There are few signaling within the protocol to specify versions or capabilities. The expectation is that systems will continue to run largely unmodified for many years, often only changing when hardware fails.
This limitation has had impact beyond the DNS itself, as the role of DNS in the larger Internet is limited by current capabilities.
In addition to making extensions or improvements to the protocol difficult, the inflexibility of DNS has had security implications. Vulnerabilities in the protocol itself are basically impossible to fix completely, resulting in long-lasting weaknesses in the wider Internet.
The new minimum requisite features must include the capability to communicate versions as well as capability negotiation between any two end-points.
Like any other service on the Internet the DNS is vulnerable to denial of service attacks today. However, it is both the target of these attacks and used as an unwilling accomplice by those launching attacks on other systems.
In order to defend against DoS attacks, DNS systems must be heavily over-provisioned, constantly monitored, or both. An ideal protocol would be able to defend itself against DoS and avoid being used as a vector to attack other systems. One feature to consider in this regard easing capability to provide end-point validation.
Since DNS is used to locate servers, it is used by CDN and anyone wishing to provide a better user experience. Protocols that perform services that users want can be delivered in customized to that user. For example, traffic can be routed to servers that are closer, less busy, or otherwise provide a faster response.
Recently the ability to include some information about the device network has been added, which provides part of this benefit. This is a very limited step, partially due to difficult privacy concerns.
Beyond this, devices have no way to describe the environment they are operating in. For example, the network of one mobile device may have different qualities than that of different mobile device or a fixed device. All queries are the same in the current DNS.
Currently there are no ways to express user preferences in the DNS. In addition to faster service, privacy concerns or other desires have no way to be declared and must be handled by later protocols.
These two aspects are often in conflict, so a solution must enable both under user control.
The DNS has almost no information about the DNS servers themselves. There is no way for authoritative servers to publish their capabilities. The recursive resolvers and stub resolvers have only minimal ability to declare what they can do (limited to UDP buffer sizes and DNSSEC support) or how they are configured.
This means that servers must infer how the various systems work, which is currently done by repeatedly scanning remote capabilities (for example EDNS buffer size adjustment). The lack of explicit information means that the process is inefficient and occasionally results in very sub-optimal behavior or even complete failure.
At no point is any DNS data encrypted. Queries and answers are cleartext, as is zone data replicated between servers. This means that both passive and active snooping of the DNS is almost trivial.
Certain kinds of traffic analysis will likely always be possible given that servers act as proxies in the DNS architecture. For example, caching resolvers see the queries of stub resolvers. Without proxies the traffic analysis risk is still present, although different since then queries would need to come directly from end users' devices.
To avoid errors derived from partial information publication the new unit of data transfer must be the equivalent of today's RRsets rather than individual records.
DNS has a protocol to share data between authoritative servers. This protocol has a number of limitations. It does not provide a way to add or remove servers within a given label. It provides very few ways for parent and child zones to synchronize. It scales quite poorly with large numbers of zones, and DNSSEC data can greatly increases the amount of data to periodically synchronize.
DNS has a very few tools for administrators to understand DNS problems. For example, the ServFail code is used to cover a huge number of possible problems without any details, meaning operators must try to infer the true problem. Likewise there are few methods that operators can use to figure out the state of the various servers, caches, and so on in the system.
Some things just don't make sense and can probably be removed with extreme prejudice.
There are other areas that might be explored.
Currently a single label is managed by a single organization. Protocols like Bitcoin have proven that distributed management is possible. This could be useful for politically contentious zones like the root zone, or act as an alternate model instead of a registry/registrar split for large zones.
Many name servers use anycasting today, where a single IP address is served from separate physical locations. There may be alternate ways to get DNS data closer to where it needs to be than relying on the routing system. Or, if DNS does interact with the routing world, perhaps there are smarter ways to do it.
Today the DNS always provides the latest & greatest versions of information. This matches the original intent of supporting other protocols need to map host names to IP addresses. However other uses may benefit from knowing prior values of DNS data.
DNS is an important part of the Internet. It may not be more important than the number system, or the routing system, or the servers or other devices on the network. However, the DNS has a few features that make it important in the business and political realms:
For the most part the business and political interests allow the technical folks in the DNS free reign, although this may not be true if technology changes appear to threaten their goals.
DNS can evolve.
DNS can be changed in ways that work with old servers and software, and still provide real benefits to organizations and individuals able and willing to upgrade.
DNS can be changed in steps. It can be experimented with. Mistakes can be made, and mistakes can be fixed.
Thanks to João Damas for review and suggestions.