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Bug#801507: openssh-server: Logins to SSH are slow (not DNS)

Package: openssh-server
Version: 1:6.0p1-4+deb7u2
Severity: normal

Dear Maintainer,

Here is timing (in seconds per line of debug output) log for login to
my SSHD server at host which I denote XXX.org.
Keys are replaced with YYY. It is way too slow.

$ ssh -v root@XXX.org 'echo -n' 2>&1| perl -MTime::HiRes=time -p -e '$oldtime//=time; print time-$oldtime, " "' 
4.05311584472656e-06 OpenSSH_6.9p1 Debian-2, OpenSSL 1.0.2d 9 Jul 2015
3.31401824951172e-05 debug1: Reading configuration data /etc/ssh/ssh_config
4.1961669921875e-05 debug1: /etc/ssh/ssh_config line 19: Applying options for *
0.0155961513519287 debug1: Connecting to XXX.org [] port 22.
0.17785906791687 debug1: Connection established.
0.178133964538574 debug1: identity file /home/porton/.ssh/id_rsa type 1
0.178153991699219 debug1: key_load_public: No such file or directory
0.178158044815063 debug1: identity file /home/porton/.ssh/id_rsa-cert type -1
0.17829704284668 debug1: identity file /home/porton/.ssh/id_dsa type 2
0.178317070007324 debug1: key_load_public: No such file or directory
0.178322076797485 debug1: identity file /home/porton/.ssh/id_dsa-cert type -1
0.178330183029175 debug1: key_load_public: No such file or directory
0.178335189819336 debug1: identity file /home/porton/.ssh/id_ecdsa type -1
0.178340196609497 debug1: key_load_public: No such file or directory
0.178344011306763 debug1: identity file /home/porton/.ssh/id_ecdsa-cert type -1
0.178415060043335 debug1: key_load_public: No such file or directory
0.178436040878296 debug1: identity file /home/porton/.ssh/id_ed25519 type -1
0.178440093994141 debug1: key_load_public: No such file or directory
0.178444147109985 debug1: identity file /home/porton/.ssh/id_ed25519-cert type -1
0.178505182266235 debug1: Enabling compatibility mode for protocol 2.0
0.178516149520874 debug1: Local version string SSH-2.0-OpenSSH_6.9p1 Debian-2
0.346481084823608 debug1: Remote protocol version 2.0, remote software version OpenSSH_6.7p1 Debian-5
0.34649395942688 debug1: match: OpenSSH_6.7p1 Debian-5 pat OpenSSH* compat 0x04000000
0.346500158309937 debug1: Authenticating to XXX.org:22 as 'root'
0.348556041717529 debug1: SSH2_MSG_KEXINIT sent
0.507776021957397 debug1: SSH2_MSG_KEXINIT received
0.507788181304932 debug1: kex: server->client chacha20-poly1305@openssh.com <implicit> none
0.507797002792358 debug1: kex: client->server chacha20-poly1305@openssh.com <implicit> none
0.51166296005249 debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
0.695590019226074 debug1: Server host key: YYY
0.699064970016479 debug1: Host 'XXX.org' is known and matches the ECDSA host key.
0.69907808303833 debug1: Found key in /home/porton/.ssh/known_hosts:30
0.705465078353882 debug1: SSH2_MSG_NEWKEYS sent
0.705478191375732 debug1: expecting SSH2_MSG_NEWKEYS
0.705487966537476 debug1: SSH2_MSG_NEWKEYS received
0.705492973327637 debug1: Roaming not allowed by server
0.705497026443481 debug1: SSH2_MSG_SERVICE_REQUEST sent
1.06489396095276 debug1: SSH2_MSG_SERVICE_ACCEPT received
1.23194813728333 debug1: Authentications that can continue: publickey,password
1.23197102546692 debug1: Next authentication method: publickey
1.23197507858276 debug1: Offering RSA public key: /home/porton/.ssh/id_rsa
1.39787101745605 debug1: Server accepts key: pkalg ssh-rsa blen 279
1.58550310134888 debug1: Authentication succeeded (publickey).
1.58552598953247 Authenticated to XXX.org ([]:22).
1.58553504943848 debug1: channel 0: new [client-session]
1.58554410934448 debug1: Requesting no-more-sessions@openssh.com
1.58556413650513 debug1: Entering interactive session.
1.74791097640991 debug1: Sending environment.
1.74793004989624 debug1: Sending env LC_PAPER = en_US.UTF-8
1.74793696403503 debug1: Sending env LC_MONETARY = en_US.UTF-8
1.74794602394104 debug1: Sending env LC_NUMERIC = en_US.UTF-8
1.74797606468201 debug1: Sending env LANG = en_US.utf8
1.74798607826233 debug1: Sending env LC_MEASUREMENT = en_US.UTF-8
1.74801111221313 debug1: Sending env LC_TIME = en_US.UTF-8
1.74802112579346 debug1: Sending command: echo -n
1.9185950756073 debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
1.91861510276794 debug1: client_input_channel_req: channel 0 rtype eow@openssh.com reply 0
1.91863608360291 debug1: channel 0: free: client-session, nchannels 1
1.91869902610779 debug1: fd 1 clearing O_NONBLOCK
1.91870999336243 Transferred: sent 3564, received 1788 bytes, in 0.3 seconds
1.91871905326843 Bytes per second: sent 10698.4, received 5367.2
1.91872715950012 debug1: Exit status 0

Note that this seems NOT to be a DNS issue as I have "UseDNS no" in

/etc/ssh/sshd_config follows:

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin yes
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile	%h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Subsystem sftp /usr/lib/openssh/sftp-server

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes

UseDNS no

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