Terrain, distance, and property rights
often limit LAN cabling. Where coax is restricted, network connections
can be made by serial lines. Serial lines are relatively inexpensive
and easy to install. However, you need special software, such as
PPP, to run TCP/IP applications over a serial line.
Properly installed and configured, PPP and the HP-UX system's
serial port connections allow you to transmit data to remote locations
through a modem or null-modem cable. (HP-UX systems are equipped
with internal modems, although you can use a cable to connect an
external modem or other system to a serial port.)
PPP provides an easy and flexible means of creating wide-area
TCP/IP-based networks for transfering data among UNIX systems, and
between UNIX systems and other systems that implement the PPP or
SLIP protocols. You can use PPP to connect HP-UX systems to established
TCP/IP networks. You can also use PPP to connect your HP-UX systems
to a hub; this allows the HP-UX systems transparent, dial-in access
to the hub and other LAN-connected hosts. Because of the transparency
of TCP/IP internetwork routing, users may be unaware that remote
facilities are not directly connected to the local network.
PPP includes
a command program ( named pppd),
a startup script, and a number of sample configuration files. You
can use PPP to:
Dial-in to HP 9000 serial IP lines.
Dial-out from HP 9000 serial IP lines.
Direct connect to HP 9000 serial IP lines.
Dialing In to an HP 9000 |
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Users
at remote supported terminals or PCs can establish dial-in IP connections
with logins. For a login connection, the user establishes a modem
link to an HP 9000 and logs in as usual. After login, the Login
shell script is run. The script starts pppd
on the local system which will communicate with the pppd
on the peer. The two pppd's
will negotiate and establish a PPP connection.
For a connection without a login, the user simply dials in
to a preset HP 9000 serial line where the serial protocol is already
running on the line.
Dialing Out from an HP 9000 |
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HP
9000 users can establish dial-out IP connections with or without
login. This may be to any remote host that runs a supported serial
IP protocol.
For a login connection, the user simply invokes pppd
at the HP-UX shell prompt. pppd
establishes a modem link to the specified host and logs in. pppd
runs a command on the remote machine to initiate the specified serial
IP protocol and establish the connection.
For a connection without login, the user's action
is the same. After the user invokes pppd,
a preset line is assigned to that user. The user has full network
access to the remote host.
Direct Connections |
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You,
the system administrator, may set up a direct (hardwired) IP connection
between an HP 9000 and a remote host. In effect, this is simply
a long distance extension of the LAN.
HP-UX PPP Features |
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PPP
on HP-UX offers the following features:
On demand dial-up connections. PPP
can establish an asynchronous link over standard telephone lines
whenever traffic warrants a call. This is in contrast to network
routers that require an expensive leased line to provide a constant
connection. When the traffic has completed, PPP can hang up the
connection to save the telephone costs. User applications cannot
distinguish between an on-demand dialup link and one that is constantly
maintained, except by looking at the clock.
Link traffic control. The HP-UX system administrator
has complete control over the traffic that is allowed to traverse
the link. PPP can turn an HP-UX system into a selective-isolation
packet filtering "firewall" gateway, enhancing
the security provided to other systems on the local network.
Minimizes transmission overhead. PPP compresses
HDLC address control and protocol fields, as well as TCP headers.
This improves both throughput and interactive response on typical
modem connections. The PPP interface to HP-UX TCP/IP implements
Van Jacobson's TCP "fast queue" scheme,
whereby interactive packets have priority to transmission on a congested
link.
PPP does not support traffic encryption.
pppd
is the daemon process provided with PPP to manage connections to
other hosts via the point-to-point or SLIP protocols. It uses the
HP-UX native serial ports. The daemon communicates with the HP-UX
Kernel's TCP/IP stack via an IP network tunnel driver.
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