# Shepherd Writeup for Alt-Svc
## 1. Summary
Mike Bishop is the document shepherd; Barry Leiba is the responsible
This document specifies a method to provide clients authoritative access
to HTTP origins at a different network location and/or using a different
The requested publication type is Proposed Standard.
## 2. Review and Consensus
The document started as an individual draft which provided a potential
solution to several related problems in the HTTP space, helping clients
become aware of multiple network or protocol endpoints for an origin
that could serve the same content in different ways. It drew inspiration
from an existing proprietary solution, Alternate-Protocol, used by
Chromium during SPDY development.
There was implementation interest from Mozilla Firefox and Akamai, along
with willingness from Google Chrome to migrate from Alternate-Protocol
to Alt-Svc. Other implementers were less interested, but as the behavior
is fully optional for clients, the consensus was to adopt the document.
During the HTTP/2 standardization process, the Alt-Svc document was
discussed and worked on in parallel; HTTP/2-specific pieces were
originally added to the HTTP/2 specification at the time of adoption,
but were moved into this document after HTTP/2's extension story was
There has been some interest in defining additional ways to discover
Alternative Services, and this document intentionally does not close the
door on that. It discusses client behavior when dealing with
Alternatives of which it is aware, and defines two possible ways a
client can learn about Alternatives. Future drafts may define additional
ways, such as DNS.
Technical discussions involved a broad section of the working group,
with the most focus from a few client and proxy implementers. There has
been some back and forth about the right balance between utility and
security, but the document now reflects general consensus. This is
reflected by a thoroughly-discussed Security Considerations section,
which covers ways in which Alt-Svc could be used to track clients or
persist attacks, and gives guidance to implementations on ways to
minimize the potential impacts.
## 3. Intellectual Property
Each author has stated that their direct, personal knowledge of any IPR
related to this document has already been disclosed, in conformance with
BCPs 78 and 79.
No disclosures have been submitted regarding prior work in this space.
## 4. Other Points
There are no downward references. The IANA Considerations are clear, and
the Expert Reviewers for the existing registries have been actively
involved in the draft process. A new registry is also created for
parameters modifying properties of Alt-Svc listings.
There was some discussion over whether parameters would be
mandatory-to-understand (ignoring the entire entry otherwise), or always
optional. In the end, parameters were made optional-to-understand in all
cases, to avoid exploding the list of alternatives when multiple
optional parameters were used.