Subject: [Doh] DOH behind caching proxies

From: manu tman <[email-masked]>
Date: Thu, 18 Jan 2018 16:15:08 -0800

Hi list,

Should we clarify the behaviour of caching proxies?

When using a proxy in front of DOH servers and doing targeting based on
resolver IP or using ECS, the returned answer for a same query (body param)
may be different depending on the client, but if the caching proxy caches
based on GET parameters, there is chances to return answers that are
supposed to be correct for another client.

In draft-ietf-doh-dns-over-https-02

Section 5:
```Using the GET method

   is friendlier to many HTTP cache implementations.
```
and

```

In order to maximize cache friendliness, DNS API clients using media
   formats that include DNS ID, such as application/dns-udpwireformat,
   SHOULD use a DNS ID of 0 in every DNS request.

```

As much as we may instruct the client to cache the result, if there is
proxies in the middle, those should not cache the answer they received
from backend DOH servers.

Manu