PPP uses a frame format that includes a protocol field. The protocol
field identifies the protocol (for example, IP, DECnet, or OSI) to be
used for communication between the two hosts. PPP defines the network
frame in a 5-byte header and 3-byte trailer. The PPP frame starts and
ends in the control byte 7E hex (126 decimal). The address and control
bytes are constant. The 2-byte protocol field indicates the contents of
the PPP frame.
3.2 Setting Up a PPP Interface
Use the following commands to configure the PPP interface:
Table 3-1 shows the command qualifiers used for configuring PPP interfaces.
| Qualifier | Description |
|---|---|
| /COMPRESS=[ON|OFF|AUTO] | Optional. Default=ON. Use to negotiate header compression. |
| /DESTINATION= host_name| IP_address |
Optional. Default: No destination host. If you do not specify the
remote host's address, PPP will obtain the correct address from the
remote host.
If the local host is used as a dialup provider, this command is used to specify an IP address for a remote client. In this case, you must also specify your local host address with the /HOST qualifier. |
| /HOST=[ host_name | IP_address] | Required when setting up a host as a dialup provider. Optional otherwise. Local host name or IP address using the interface. If your host is multihomed, specify an address. If not specified, PPP obtains the correct address from the remote host. |
| /NETWORK_MASK= IP_address | Optional. The subnet mask of the local PPP interface in dotted-decimal notation. |
| /SERIAL_DEVICE= device | Required for hard-wired or dedicated modem connections. Identifies the OpenVMS device name assigned to the PPP interface, for example, TTA1. |
Your OpenVMS Alpha system provides a PPP utility (PPPD) that lets you initiate and control a PPP connection from an OpenVMS Alpha host. After configuring a PPP interface, you can use the PPP utility to
Use the DCL command PPPD to invoke the PPP utility. The PPPD commands listed in Table 3-2, allow users to set and display device characteristics, connect and disconnect a PPP session, and establish a connection with a new system. For more detailed information about PPPD commands, see the TCP/IP Networking on OpenVMS manual in the OpenVMS documentation set.
| Command | Function |
|---|---|
| CONNECT | Establishes a network connection through the current physical port or a specified remote port. |
| DIAL_OUT | Allows direct access to a device in order to dial out over a modem or link to an external device. |
| DISCONNECT | Terminates the network connection and returns control to the terminal driver. |
| EXIT | Leaves the utility and returns you to the DCL command prompt ($). |
| HELP | Displays help text for PPPD commands. |
| SET | Determines the device and line characteristics for the specified terminal. |
| SHOW | Displays the device and line characteristics of the specified terminal. |
You can configure your host to answer calls, assign IP addresses, and establish connections initiated by users on remote hosts or PCs. To set up your host as a PPP provider, configure your interface for PPP with the /HOST, /SERIAL_DEVICE, /NETWORK_MASK and /DESTINATION qualifiers to the SET INTERFACE command. For example:
$ SET TERMINAL TTA2 /PERMANENT /DISCONNECT
SET INTERFACE PPn /SERIAL_DEVICE=TTn /HOST=IP_address /DESTINATION=IP_address
UCX> SET PROTOCOL IP /FORWARD UCX> SET CONFIGURATION PROTOCOL IP /FORWARD
UCX> START ROUTING /SUPPLY UCX> SET CONFIGURATION START ROUTING /SUPPLY
You can establish a PPP connection with a remote terminal server without specifying its IP address or configuring the serial interface on your local system. In such a case, the remote server will provide your host with an IP address after the connection is established.
The following example shows how to use the PPP utility (PPPD) to dial out to a terminal server.
$ PPPD DIAL_OUT TTA1
Type control-~ to send a break
control-\ to disconnect
control-@ to switch to a Point-to-Point connection.
atd 8671234
#
LOCAL> CONNECT PPP
Local -561- Starting SLIP or PPP datalink session
%PPPD-I-CONNECTTERM, converting connection on device _TTA1: to a
Point-to-Point connection
To terminate a PPP connection, follow these steps:
After the connection is terminated, and OPCOM message displays. For example:
%%%%%%%%%%% OPCOM 23-APR-1997 15:44:32.10 %%%%%%%%%%% Message from user XYZnet on JONES %UCX-S-PPPDISCONN, Disconnected PPP Interface PP1 on TTA1
Configuring the network interface for SLIP is equivalent to configuring the interface for Ethernet connections. In this case, the network interface is the modem connection. Remember, before configuring a SLIP line, you must choose an IP address for the interface at each end of the line and establish a physical connection.
Use the following commands to set up the SLIP interface:
Table 3-3 shows the command qualifiers used for configuring SLIP interfaces.
| Qualifier | Description |
|---|---|
| /[NO]AUTO_START | Optional. Default: /AUTO_START. Automatically creates the interface upon UCX startup. |
/COMPRESS=
|
Optional. Default: No compression. Enables or disables TCP header compression (CSLIP). With /COMPRESS=AUTOMATIC, compression remains off unless the remote host begins to use it. |
| /[NO]FLOWCONTROL |
Optional. Default: No flow control. Enables the special handling of XON
and XOFF characters to work properly with modems that are configured to
interpret these characters locally.
Specify /FLOWCONTROL only if the host at the other end of the line is another host running DIGITAL TCP/IP Services for OpenVMS. If you cannot use /FLOWCONTROL, configure your modem to pass all the XON and XOFF characters through transparently. |
| /HOST=( host_name, IP_address) | Required. Host name or IP address of the local host. If your host is multihomed, you must specify an address in dotted-decimal notation. |
| /NETWORK_MASK= subnet_address | Required. The subnet mask of the local SLIP interface in dotted-decimal notation. |
| /SERIAL_DEVICE= device |
Required for hard-wired or dedicated modem connections. Optional for
dynamic connections.
Identifies the OpenVMS device name assigned to the SLIP interface, for example, TTA1. |
For example, the following command configures SLIP interface SL5, using the local IP address assigned to host CROW, with a subnetwork mask of 255.255.255.0. The interface uses the terminal device TTA3:. /COMPRESS enables TCP header compression (CSLIP). /FLOWCONTROL enables special handling of XON and XOFF characters.
UCX> SET INTERFACE SL5 /HOST=CROW /NETWORK_MASK=255.255.255.0 - _UCX> /SERIAL_DEVICE=TTA3 /COMPRESS=ON /FLOWCONTROL
To configure SLIP with hard-wired lines, follow these steps:
You can configure either a terminal server port or an OpenVMS system itself to answer dial-in calls.
Follow these steps:
$ SET TERMINAL TTA2 /PERMANENT /MODEM /NOHANGUP
$ SET TERMINAL TTA2 /PERMANENT /NOTYPEAHEAD
$ SET TERMINAL TTA2 /PERMANENT /NOAUTOBAUD /SECURE_SERVER
$ SET HOST /DTE terminal_name
ATDT telephone_number
The following example shows a user named SLIP-USER, at a PC named ROBIN and with a 9600-baud modem, using terminal device TTA2 and connecting it to the port of a terminal server. In this example:
$ SET HOST /DTE TTA2 %REM-I-TOQUIT, connection established Press Ctrl/\ to quit, Ctrl/@ for command mode ATDT 2222222 CONNECT 9600 # hootowl (not echoed) Network Access SW V1.5 for DS700-16 (c) Copyright 1994, Digital Equipment Corporation - All Rights Reserved Please type HELP if you need assistance Enter username> SLIP-USER Local> CONNECT SLIP Ctrl/\ $ UCX SET INTERFACE SL2 /HOST=1.2.3.4 /NETWORK_MASK=255.255.255.0 - _UCX> /SERIAL_DEVICE=TTA1: /COMPRESS=ON
You can configure your host to answer calls and establish connections initiated by users on remote hosts.
To set up your host as a SLIP provider:
$ UCX SET INTERFACE SL5 /HOST=192.208.35.5 /SERIAL_DEVICE=TT
As soon as you log out, your terminal port becomes a SLIP interface. Without causing the modem to hang up, start SLIP on the remote system.
To facilitate connection setup for end users, create a dedicated user name for each remote host that dials in. These users need to have a LOGIN.COM procedure that issues appropriate SET TERMINAL and UCX SET INTERFACE commands, terminating with a LOGOUT command. Every user should specify a different SLIP interface name and host name (or IP address). These users require the OPER privilege in order to create interfaces.
You can enable IP forwarding on the SLIP provider host and start dynamic routing. As appropriate, issue:
$ UCX SET PROTOCOL IP /FORWARD $ UCX SET CONFIGURATION PROTOCOL IP /FORWARD
To send notifications automatically on all connected LANs when new hosts or networks become reachable, use dynamic routing with the /SUPPLY option. For example, every time a SLIP connection is set up to a new remote subnetwork, RIP (Routing Information Protocol) advertises a corresponding route. As appropriate, issue:
$ UCX START ROUTING /SUPPLY $ UCX SET CONFIGURATION START ROUTING /SUPPLY
You can make your SLIP-connected host appear as if it were directly connected to the LAN. This is possible using a proxy ARP server --- usually the same host that is acting as a SLIP gateway into the LAN.
To use proxy ARP (Address Resolution Protocol), assign to the remote host an IP address in the same subnetwork as the LAN. As other hosts on the LAN attempt to communicate with the remote host, the SLIP gateway answers ARP queries for the remote host by giving its own LAN address. The gateway then forwards packets across the SLIP line.
Many DIGITAL DECserver terminal server products support SLIP connections and implement proxy ARP. If you dial in from an OpenVMS host to a terminal server, the terminal server automatically detects your IP address and begins responding to ARP queries, forwarding packets as necessary.
To use proxy ARP with a DECserver terminal server, assign an IP address in the same subnetwork as the terminal server.
On the terminal server, issue the SHOW PORT SLIP command. Verify that:
It is also possible to set up your host as a SLIP gateway with proxy ARP. You might prefer this approach if your dial-in modems are attached directly to an OpenVMS system, rather than to a terminal server.
Follow these steps on the host to become a SLIP gateway:
$ UCX SET INTERFACE SL0 /HOST=10.1.2.3 /SERIAL_DEVICE=TTA2
$ UCX SET ROUTE FINCH /GATEWAY=10.1.2.3
$ UCX SET ARP 08-00-2B-2C-4F-46 FINCH /PUBLIC
$ UCX SET PROTOCOL IP /FORWARD
When your host is set up as a SLIP gateway, create an interface on the remote host at the other end of the serial line. Specify an address in the same subnetwork as the LAN.
Although the two ends of the SLIP line are in different subnetworks,
traffic can flow properly due to the interface route you added with the
SET ROUTE command.
3.3.6 Shutting Down SLIP
To terminate a SLIP connection, follow these steps:
$ UCX SET NOINTERFACE interface
See Section A.10.
Routing allows traffic from your local network to reach its destination elsewhere on the internet. All hosts and gateways on a network use routing protocols to exchange and store routing information. Routing is simply the act of forwarding datagrams based on information stored in a routing table.
The DIGITAL TCP/IP Services for OpenVMS product provides two types of
routing: static and dynamic. This chapter reviews key routing concepts
and describes how to configure static or dynamic routing on your system.
4.1 Reviewing Key Concepts
If the hosts on your network need to communicate with computers on other networks, a route through a gateway must be defined. All hosts and gateways on a network store routing information in routing tables. With DIGITAL TCP/IP Services for OpenVMS, routing tables are implemented in dynamic and permanent databases.
You can define routes manually (called static routing) or you can enable the Routing Information Protocol (RIP), which builds route information based on information received by means of RIP updates from remote hosts. This is called dynamic routing.
The following sections serve as a review only. If you are not familiar
with routing concepts, see DIGITAL TCP/IP Services for OpenVMS
Concepts and Planning or other introductory documentation for more
information.
4.1.1 Static Routing
Static routing tables are most useful when the number of gateways is
limited. Static routing does not adjust to changing network conditions;
each change is made manually by the network manager. Because static
routing tables do not adjust to network changes, use static routing
only where routes do not change.
4.1.2 Dynamic Routing
Complex environments require a more flexible approach to routing than a static routing table provides. Routing protocols handle complex routing situations more quickly and accurately. Dynamic routing tables use information received by means of RIP updates; when routes change, RIP updates provide information on the changes.
DIGITAL TCP/IP Services for OpenVMS software implements RIP in its dynamic routing server. This server, similar to the UNIX routing daemon routed, sends and receives RIP messages. Using this information, the server dynamically builds the routing table based on the information received through RIP updates.
When the server starts, it issues routing update requests then listens
for responses. A system configured to supply RIP information responds
to the request with an update packet. The update packet contains
destination addresses and routing metrics associated with each
destination. After receiving a RIP update, the routing server uses the
information to update its routing table.
4.2 Setting Up Routing
If you select to enable dynamic routing during the UCX configuration procedure, the routing software does not require any management.
However, the routing function requires manual management if you do not
enable dynamic routing and you want to communicate outside of your
local subnetwork. In addition, you can optionally monitor and
reconfigure routing.
4.2.1 Routing Management Commands
To create routes manually, reconfigure routing, and monitor routing, use the following commands:
To start and stop dynamic routing, use the commands listed in Table 4-1.
| Command | Function |
|---|---|
| START ROUTING | Starts dynamic routing and configures your host to receive RIP messages. |
| START ROUTING /SUPPLY | Starts dynamic routing and configures your host to both receive and supply RIP messages. |
| STOP ROUTING | Stops your hosts from receiving RIP messages. |
| SET CONFIGURATION START ROUTING | Same as START ROUTING; starts dynamic routing at UCX startup. |
The first time you run the configuration procedure, UCX$CONFIG.COM, static routing is configured automatically. To manually configure static routing, use the CREATE ROUTE command to create an empty routes database file. The default file name is SYS$COMMON:[SYSEXE]UCX$ROUTE.DAT. To specify a different name, define the systemwide logical name UCX$ROUTE. When the routes database file is created, it is assigned a version number of existing_file +1.
Important
Do not execute the CREATE ROUTE command unless you intend to reconfigure your entire cluster.
To create a static route, use the SET ROUTE command. The command has the following effects:
The command requires the following information:
DIGITAL strongly recommends that you do not specify alias names with the destination parameter or the /GATEWAY=host qualifier.
If you are running dynamic routing, you cannot use SET NOROUTE to remove a route that is maintained by the routing server. In such an instance, issue the command STOP ROUTING before executing the SET NOROUTE command.
To define a route to any host on a specific network, issue:
UCX> SET ROUTE network_IP_address /GATEWAY="gateway" /NETWORK
To define a route to a specific host on a specific network, issue:
UCX> SET ROUTE remote_host /GATEWAY="gateway"
Example 1:
In the following example, the network is active. The SET ROUTE command
adds a route to the volatile routes database. UCX starts directing
communication for flamingo through gateway francolin.
UCX> SET ROUTE "flamingo" /GATEWAY="francolin"
Example 2:
In the following example, the network is active. The SET ROUTE command
defines a routing path in the volatile routes database. The command
specifies that traffic for the network with IP address 128.30.0.0 use
gateway francolin.
UCX> SET ROUTE 128.30.0.0 /NETWORK /GATEWAY="francolin"
Example 3:
In the following example, the network is not active. The SET ROUTE
command adds the new route to the permanent routes database. The next
time UCX starts up, packets for NENE will go through a gateway called
bird.of.paradise.
UCX> SET ROUTE NENE /GATEWAY="bird.of.paradise"
At UCX startup, the information in the permanent routes database, if any exists, is loaded into the volatile routes database. You can add permanent routes while UCX is stopped or while it is running. If it is running, use the /PERMANENT qualifier.
Example 4:
The following command permanently sets routing for host
albatross to go through gateway birdygate.
UCX> SET ROUTE "albatross" /GATEWAY="birdygate" /PERMANENT