I just upgraded two machine from 1.5E -> 1.5S
I therefore changed from ssh 1.2.27 to the in-tree one.
AFAICT all I needed to do was add /etc/ssh{,d}.conf and
umask 022
/usr/bin/ssh-keygen -d -f /etc/ssh_host_dsa_key -N ''

On one machine all was OK, but the other gives:

OpenSSH_2.5.1 NetBSD_Secure_Shell-20010219, SSH protocols 1.5/2.0, OpenSSL 0x0090581f
debug: Reading configuration data /home/prlw1/.ssh/config
debug: Reading configuration data /etc/ssh.conf
debug: Rhosts Authentication disabled, originating port will not be trusted.
debug: ssh_connect: getuid 1234 geteuid 1234 anon 1
debug: Connecting to john [111.222.333.444] port 22.
debug: Connection established.
debug: identity file /home/prlw1/.ssh/identity type 3
debug: identity file /home/prlw1/.ssh/id_dsa type 3
ssh_exchange_identification: Connection closed by remote host
debug: Calling cleanup 0x8057184(0x0)

The next lines would have been:

debug: Remote protocol version 1.99, remote software version OpenSSH_2.5.1 NetBSD_Secure_Shell-20010219
debug: match: OpenSSH_2.5.1 NetBSD_Secure_Shell-20010219 pat ^OpenSSH
debug: Local version string SSH-1.5-OpenSSH_2.5.1 NetBSD_Secure_Shell-20010219

if it had been working. Any clues as to where to look?

Cheers,

Patrick