ALPN
Application-Layer Protocol Negotiation (ALPN) is a TLS extension which indicates what application layer protocol is negotiating the encrypted connection without requiring additional round trips.
| Protocol | Identification sequence |
|---|---|
| HTTP/1.1 | 0x68 0x74 0x74 0x70 0x2F 0x31 0x2E 0x31 ("http/1.1") |
| HTTP/2 | 0x68 0x32 ("h2") |
| HTTP/2 over cleartext TCP | 0x68 0x32 0x63 ("h2c") |
Specifications
| Specification | Status | Notes |
|---|---|---|
| RFC 7301 | IETF RFC | Initial definition. |