Re: Slow PPP/SLIP bug: Found change that caused problem

Arnt Gulbrandsen (
Thu, 4 Apr 1996 16:09:26 +0200 (Christoph Lameter)
> Alan Cox ( wrote:
> : > telnet connections using TCP/IP are slow, but if I use
> : > ssh (secure telnet) all is fine.
> : >
> : > ssh has its own packet handling and bypasses TCP.
> : No
> Yes. SSH uses TCP socket number 20 to establish the connection but then
> switches to something they call the "binary protocol" to do the
> actual transmissions in a secure way.

No. SSH uses TCP port number 22, first to authenticate the user,
negotiate encryption and s on, then as a transport for the "packet
based binary protocol" you talk about.

FYI, most modern TCP-based protocols I've seen use more or less the
same technique, line-based protocols like SMTP are a little old hat.

And port 20 is used for FTP data connections.