< HTTP/1.1 506 Variant Also Negotiates

TL;DR: 506 means the server’s content negotiation is circular: a variant it wants to serve is itself negotiated. It comes from RFC 2295 (transparent content negotiation), is almost never produced by modern stacks, and when it does show up the cause is a misconfigured Apache type map or MultiViews setup.

What it means

Content negotiation picks one representation of a resource (for example /doc as doc.en.html or doc.fr.html) based on Accept-Language and similar request headers. RFC 2295 defined a protocol for doing this transparently across caches, with a Negotiate header and variant lists. A resource used to choose among variants must point at concrete variants. If a chosen variant is itself a negotiating resource, the process can recurse, so the server answers 506 (RFC 2295 §8.1).

GET /docs/guide HTTP/1.1
Host: example.com
Accept-Language: fr

HTTP/1.1 506 Variant Also Negotiates
Content-Type: text/html

Where you might see it

Apache’s mod_negotiation returns it with an error message to the effect that a variant for the resource is itself a negotiable resource, which indicates a configuration error. That happens when:

• a type-map file (.var) lists a URI that itself resolves through another type map, or
• MultiViews picks a file that Apache then treats as a negotiated resource again, for example because a handler maps the matched name back into a negotiated path.

Check the Apache error log for the exact message, then follow the variant’s target. A flat type map looks like this:

# type map for /docs/guide
URI: guide.en.html
Content-type: text/html
Content-language: en

URI: guide.fr.html
Content-type: text/html
Content-language: fr

Every URI: should be a concrete file. If guide.fr.html were itself a .var file with more variants, you would be in 506 territory.

Fix

1. Identify the resource and open its type map or look at the files MultiViews would match.
2. Replace nested type maps with a flat list of concrete files.
3. If the negotiation involves rewrites, make sure a rewrite does not send the chosen variant back through the negotiated path.
4. Disable what you do not use: Options -MultiViews makes Apache stop negotiating by filename.

Try it with curl

506 Variant Also Negotiates comes from transparent content negotiation (RFC 2295), which is almost never deployed, so you cannot trigger it on demand. If a server sends one, curl -i shows it; the cause is a server misconfiguration, not something your request did.

curl -i -H 'Accept: text/html' https://example.com/resource

Related

• 406 Not Acceptable: no variant matches the request.
• 300 Multiple Choices: the server offers variants.
• 500 Internal Server Error
• Accept-Language and Vary