What will happen if server implement spdy/3 while browser only support spdy/2?

Question

What will happen if I add support for spdy/3 on my server, while my users only have spdy/2 in their browsers? Will the protocol degrade gracefully to spdy/2 or it will only use plain https?

Triboelectricity

I can no longer vote to re-open, but this is an important question for those implementing the SPDY protocol. I do not think it is off-topic at Stack Overflow. – Firsthand

Answer 1

Servers that supports SPDY such as Jetty advertise the protocols that they are able to support via NPN, and usually there always is "http/1.1" among them.

If your server advertises "spdy/3","http/1.1", and the browser only supports "spdy/2", then the browser (being a browser means it supports HTTP by default) will fallback to "http/1.1" over TLS.

There is no degradation to spdy/2 if the server does not support it (spdy/2 and spdy/3 are binary incompatible). If a protocol negotiation is not possible, the connection is closed.

Mccartan

Thanks for the answer. It really helps. Is it possible for a server to support more than one version of spdy? let's say it supports both spdy/2 and spdy/3 at the same time. – Triboelectricity

Sure, it would just advertise both spdy/2 and spdy/3 via NPN, and then use whichever version the client requests. – Firsthand