ssl_ecdh_curve

This directive appeared in versions 1.1.0 and 1.0.6.

Specifies a curve for ECDHE ciphers.

When using OpenSSL 1.0.2 or higher, it is possible to specify multiple curves (1.11.0), for example:

The special value auto (1.11.0) instructs nginx to use a list built into the OpenSSL library when using OpenSSL 1.0.2 or higher, or prime256v1 with older versions.

Prior to version 1.11.0, the prime256v1 curve was used by default.