Re: [quicwg/base-drafts] introduce a version alias mechanism (#2573)

[Mike Bishop <[e-mail]>]

MikeBishop commented on this pull request.

Needs some of the extra text others have noted, plus some agreement issues.

While we will eventually need to write a full VN specification, it might also be worth mentioning some implications here.  While we're not specifying the generation algorithm, let's be pedantic and say that the server MUST NOT advertise as an alias a version number for some other version it actually speaks.  As a corollary, if the server advertises as an alias some version number that the client actually supports, the client SHOULD assume the server doesn't support that version.



> @@ -3246,7 +3246,21 @@ Implementors are encouraged to register version numbers of QUIC that they are
 using for private experimentation on the GitHub wiki at
 \<https://github.com/quicwg/base-drafts/wiki/QUIC-Versions\>.
 
-
+## Version Aliases
+
+In order to avoid ossification of the version number defined by this draft,
+servers announce a list of version numbers that they interpret as an alias for
+the version number used in this draft. Alias versions MUST NOT be a reserved
+version. Servers SHOULD send at least one version alias, and SHOULD frequently
+change the value that they announce. Each version alias contains a lifetime,
+which indicates how long the server will accept this version alias. It also
+contains an initial salt, which is used instead of the initial salt as defined
+in section 5.2 of {{QUIC-TLS}}. The list of version aliases is sent in the
+server's Transport Parameters (see {{transport-parameter-definitions}}).
+
+Clients SHOULD remember the aliases and use it for subsequent connections to the

Antecedent agreement.  Many possibilities:
- ...remember the aliases and use **them**
- ...remember the **list of** aliases and use it
- ...remember **one of** the aliases and use it

> @@ -4115,6 +4130,25 @@ preferred_address (0x000d):
 ~~~
 {: #fig-preferred-address title="Preferred Address format"}
 
+version_aliases (0x000e):
+
+: A list of version numbers that the server accepts as an alias for the
+  currently used versions. This transport parameter is only sent by the server.

```suggestion
  currently used version. This transport parameter is only sent by the server.
```

> @@ -4115,6 +4130,25 @@ preferred_address (0x000d):
 ~~~
 {: #fig-preferred-address title="Preferred Address format"}
 
+version_aliases (0x000e):
+
+: A list of version numbers that the server accepts as an alias for the

```suggestion
: A list of version numbers that the server accepts as aliases for the
```

> @@ -4115,6 +4130,25 @@ preferred_address (0x000d):
 ~~~
 {: #fig-preferred-address title="Preferred Address format"}
 
+version_aliases (0x000e):
+
+: A list of version numbers that the server accepts as an alias for the
+  currently used versions. This transport parameter is only sent by the server.
+  Every version alias contains a lifetime in milliseconds. The alias is only valid
+  for that lifetime, clients MUST NOT use it after expiry.

```suggestion
  for that lifetime. Clients MUST NOT use an expired alias.
```

Comma splice.

> @@ -3246,7 +3246,21 @@ Implementors are encouraged to register version numbers of QUIC that they are
 using for private experimentation on the GitHub wiki at
 \<https://github.com/quicwg/base-drafts/wiki/QUIC-Versions\>.
 
-
+## Version Aliases
+
+In order to avoid ossification of the version number defined by this draft,
+servers announce a list of version numbers that they interpret as an alias for

```suggestion
servers announce a list of version numbers that they interpret as aliases for
```

> @@ -3246,7 +3246,21 @@ Implementors are encouraged to register version numbers of QUIC that they are
 using for private experimentation on the GitHub wiki at
 \<https://github.com/quicwg/base-drafts/wiki/QUIC-Versions\>.
 
-
+## Version Aliases
+
+In order to avoid ossification of the version number defined by this draft,
+servers announce a list of version numbers that they interpret as an alias for
+the version number used in this draft. Alias versions MUST NOT be a reserved
+version. Servers SHOULD send at least one version alias, and SHOULD frequently
+change the value that they announce. Each version alias contains a lifetime,

This feature is being proposed to grease middleboxes; reserved versions exist to grease the peer endpoint.

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