ssh working with dialup, not through router

[Marco Fioretti]

Hello,

I can ssh to a server to update its web pages if I
connect via dialup / ppp0

If I try the same thing connecting via etho to an
ADSL router:

I can ping the server
I can browse its web pages

but ssh times out after asking the password. I
tried to ssh to another server: I got the message
saying (after my confirmation) that that host had
been added to ~/.ssh/hosts, so it seems to me
that ssh port is not being blocked. Or is it?
What could it be, and how could I figure it out?

TIA,
Marco F.