1Notes:
2
3NONE CIPHER:
4  To use the NONE option you must have the NoneEnabled switch set on the server
5  and you MUST have *both* NoneEnabled and NoneSwitch set to yes on the client.
6  The NONE feature works with ALL ssh subsystems (as far as we can tell)
7  as long as there is no tty allocated.
8  If a user uses the -T switch to prevent a tty being created the NONE cipher
9  will be disabled. 
10
11
12PERFORMANCE:
13  The performance increase will only be as good as the network and TCP stack
14  tuning on the reciever side of the connection allows.  As a rule of thumb a
15  user will need at least 10Mb/s connection with a 100ms RTT to see a doubling
16  of performance.
17  The HPN-SSH home page  http://www.psc.edu/networking/projects/hpn-ssh
18  describes this in greater detail. 
19
20
21BUFFER SIZES:
22- if HPN is disabled the receive buffer size will be set to the OpenSSH default
23  of 64K.
24
25- if a HPN system connects to a non-HPN system the receive buffer will
26  be set to the HPNBufferSize value. The default is 2MB but user adjustable.
27
28- If a HPN to HPN connection is established a number of different things might
29  happen based on the user options and conditions. 
30
31  Conditions: HPNBufferSize NOT Set, TCPRcvBufPoll enabled, TCPRcvBuf NOT Set 
32  Result: HPN Buffer Size = up to 64MB 
33    This is the default state.  The HPN buffer size will grow to a maximum of
34    64MB as the TCP receive buffer grows.  The maximum HPN Buffer size of 64MB
35    is geared towards 10GigE transcontinental connections. 
36
37  Conditions: HPNBufferSize NOT Set, TCPRcvBufPoll disabled, TCPRcvBuf NOT Set
38  Result: HPN Buffer Size = TCP receive buffer value. 
39    Users on non-autotuning systesm should disable TCPRcvBufPoll in the 
40    ssh_cofig and sshd_config
41
42  Conditions: HPNBufferSize SET, TCPRcvBufPoll disabled, TCPRcvBuf NOT Set
43  Result: HPN Buffer Size = minmum of TCP receive buffer and HPNBufferSize. 
44    This would be the system defined TCP receive buffer (RWIN).
45
46  Conditions: HPNBufferSize SET, TCPRcvBufPoll disabled, TCPRcvBuf SET
47  Result: HPN Buffer Size = minmum of TCPRcvBuf and HPNBufferSize. 
48    Generally there is no need to set both.
49
50  Conditions: HPNBufferSize SET, TCPRcvBufPoll enabled, TCPRcvBuf NOT Set
51  Result: HPN Buffer Size = grows to HPNBufferSize
52    The buffer will grow up to the maximum size specified here. 
53
54  Conditions: HPNBufferSize SET, TCPRcvBufPoll enabled, TCPRcvBuf SET
55  Result: HPN Buffer Size = minmum of TCPRcvBuf and HPNBufferSize. 
56    Generally there is no need to set both of these, especially on autotuning 
57    systems. However, if the users wishes to override the autotuning this would
58    be one way to do it.
59
60  Conditions: HPNBufferSize NOT Set, TCPRcvBufPoll enabled, TCPRcvBuf SET
61  Result: HPN Buffer Size = TCPRcvBuf. 
62   This will override autotuning and set the TCP recieve buffer to the user
63   defined value.
64
65
66HPN SPECIFIC CONFIGURATION OPTIONS:
67
68- HPNDisabled=[yes/no] client/server
69  In some situations, such as transfers on a local area network, the impact 
70  of the HPN code produces a net decrease in performance.  In these cases it is 
71  helpful to disable the HPN functionality. By default HPNDisabled is set to no. 
72
73- HPNBufferSize=[int]KB client/server
74  This is the default buffer size the HPN functionality uses when interacting
75  with non-HPN SSH installations.  Conceptually this is similar to the TcpRcvBuf
76  option as applied to the internal SSH flow control.  This value can range from 
77  1KB to 64MB (1-65536).  Use of oversized or undersized buffers can cause
78  performance problems depending on the roud trip time of the network path.
79  The default size of this buffer is 2MB.
80
81- TcpRcvBufPoll=[yes/no] client/server
82  Enable or disable the polling of the TCP receive buffer through the life 
83  of the connection.  You would want to make sure that this option is enabled 
84  for systems making use of autotuning kernels (linux 2.4.24+, 2.6, MS Vista,
85  FreeBSD 7.x and later). Default is yes.
86
87- TcpRcvBuf=[int]KB client
88  Set the TCP socket receive buffer to n Kilobytes.  It can be set up to the 
89  maximum socket size allowed by the system.  This is useful in situations where 
90  the TCP receive window is set low but the maximum buffer size is set higher
91  (as is typical).  This works on a per TCP connection basis.  You can also use
92  this to artifically limit the transfer rate of the connection.  In these cases
93  the throughput will be no more than n/RTT.  The minimum buffer size is 1KB. 
94  Default is the current system wide TCP receive buffer size.
95
96- NoneEnabled=[yes/no] client/server
97  Enable or disable the use of the None cipher.  Care must always be used when
98  enabling this as it will allow users to send data in the clear.  However, it
99  is important to note that authentication information remains encrypted even
100  if this option is enabled.  Set to no by default.
101
102- NoneSwitch=[yes/no] client
103  Switch the encryption cipher being used to the None cipher after
104  authentication takes place.  NoneEnabled must be enabled on both the client
105  and server side of the connection.  When the connection switches to the NONE
106  cipher a warning is sent to STDERR.  The connection attempt will fail with an
107  error if a client requests a NoneSwitch from the server that does not
108  explicitly have NoneEnabled set to yes.
109  Note: The NONE cipher cannot be used in interactive (shell) sessions and it
110  will fail silently.  Set to no by default.
111
112
113CREDITS:
114
115  This patch was conceived, designed, and led by Chris Rapier (rapier@psc.edu)
116  The majority of the actual coding for versions up to HPN12v1 was performed
117  by Michael Stevens (mstevens@andrew.cmu.edu).
118  The MT-AES-CTR cipher was implemented by Ben Bennet (ben@psc.edu).
119  This work was financed, in part, by Cisco System, Inc., the National Library
120  of Medicine, and the National Science Foundation. 
121