HP TCP/IP Services for OpenVMS

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3.3.4 Connecting a Host to the LAN

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 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.

At the terminal server, enter the TCP/IP management command SHOW PORT SLIP. Verify that:

3.3.5 Setting Up a SLIP Gateway with Proxy ARP

It is also possible to set up your host as a SLIP gateway with proxy ARP. You might prefer this approach if your dialin 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:

  1. Create a SLIP interface in another network or subnetwork, for example:


  2. Add a host route for the remote system. For example:


  3. Configure an ARP entry for the remote host, listing your own Ethernet address (as shown in TCPIP SHOW INTERFACE /FULL). For example:

    $ TCPIP SET ARP 08-00-2B-2C-4F-46 FINCH /PUBLIC 

  4. Enable IP packet forwarding, if not already done. Enter:


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:

  1. Return the associated terminal port to general use. Enter:


  2. If you added special route and proxy entries in conjunction with the SLIP line, remove them.
  3. If you changed any terminal settings in preparation for SLIP, restore them using the SET TERMINAL command.

3.4 Solving Serial Line Problems

If you have problems dialing in to an OpenVMS system using SLIP or PPP after following the instructions in this chapter, perform the following steps to isolate the cause of the problem:

  1. Check the equipment used by both the client and the dialin provider:
    After a software upgrade, be sure to reboot and restart TCP/IP Services.
  2. Make sure the SET HOST attempts have not exceeded the OpenVMS security level. To check and then delete, if necessary, any information about these attempts, enter the following commands. Note that SECURITY privilege must be enabled to use these commands.


  3. Make sure that IP forwarding is enabled using the following command:


  4. Make sure the terminal characteristics for the terminal device associated with the interface are set up as follows:


    Make sure you specify the /TYPE_AHEAD qualifier when you enter the SET TERMINAL command to set up an asynchronous port.

  5. Enter the SET HOST/DTE command to make sure you can log in to the system:


    If you cannot log in to or communicate with the system, you may be using the wrong terminal device name (TTnx).

  6. Set up OPCOM to receive messages using the DCL command REPLY/ENABLE. You need OPER privileges to use OPCOM.
  7. You need NETMBX and OPER privileges to establish a successful connection. If these privileges are not enabled when you enter the CONNECT command, you will see messages similar to the following:

    $ PPPD 
    \}`}"}(}"6~ <CTRL/@> 
    %PPPD-I-CONNECTTERM, converting connection on device _TTA0: to a 
    Point-to-Point connection 
    %PPPD-E-CALLBACKERR, error calling network callback 
    %SYSTEM-F-NOPRIV, insufficient privilege or object protection violation 
    %PPPD-F-ABORT, fatal error encountered; operation terminated 

    Note that the extraneous data in this sample is an ASCII representation of IP packets transmitted over the open line.
    PPP sets up a default route on the client if one did not exist. Typically, a default route exists if another interface exists on the client.

  8. Attempt to ping the remote system:

    TCPIP> PING host-name

    Watch the modem's LED display as you attempt to communicate using the PING command.
    You might not be able to ping the system if the serial line is tied up with a large FTP operation.

  9. Use the TCPTRACE command to see packets going in and out of the local system. For information about using TCPTRACE, enter:


  10. Display a count of the packets being sent and received on the problem interface, in full screen format, updated every second. For a SLIP problem, enter:


    To display the packet counts for PPP problem, enter:


    In these commands, n is the interface number.

3.4.1 Solving PPP Problems

Keep the following in mind for PPP-specific problems:

Chapter 4
Configuring and Managing Routing

Routing allows traffic from your local network to reach its destination elsewhere on the internet. Hosts and gateways on a network use routing protocols to exchange and store routing information. Routing is the act of forwarding datagrams based on information stored in a routing table.

The TCP/IP Services product provides two types of routing: static and dynamic. This chapter reviews key routing concepts and describes:

4.1 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 information about routes in routing tables. With TCP/IP Services, routing tables are maintained in both dynamic and permanent memory.

You can define routes manually (static routing), or you can enable routing protocols that exchange information and build routing tables based on the information exchanged (dynamic routing).

4.1.1 Static Routing

Because static routing requires manual configuration, it is most useful when the number of gateways is limited and where routes do not change frequently. For information on manually configuring routing, see Section 4.2.

4.1.2 Dynamic Routing

Complex environments require a more flexible approach to routing than a static routing table provides. Routing protocols distribute information that reflect changing network conditions and update the routing table accordingly. Routing protocols can switch to a backup route when a primary route becomes unavailable and can determine the best route to a given destination.

Dynamic routing tables use information received by means of routing protocol updates; when routes change, the routing protocol provides information about the changes.

Routing daemons implement a routing policy, that is, the set of rules that specify which routes go into the routing table. A routing daemon writes routing messages to a routing socket, causing the kernel to add a new route, delete an existing route, or modify an existing route.

The kernel also generates routing messages that can be read by any routing socket when events occur that may be of interest to the process, for example, the interface has gone down or a redirect has been received.

TCP/IP Services implements two routing daemons: the Routing Daemon (ROUTED) and the Gateway Routing Daemon (GATED). The following sections provide more information. Routing Daemon (ROUTED)

This daemon (pronounced route-dee) supports the Routing Information Protocol (RIP). When ROUTED 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 ROUTED uses the information to update its routing table.

To configure dynamic routing with ROUTED, see Section 4.3. Gateway Routing Daemon (GATED)

This daemon (pronounced gate-de) supports interior and exterior gateway protocols. It obtains information from several routing protocols and selects the best routes based on that information. You can configure GATED to use one or more of the protocols described in Table 4-1.

Table 4-1 GATED Routing Protocols
Protocol RFC Description
Routing Information Protocol (RIP) Versions 1 and 2 RFC 1058, RFC 1723 RIP is a commonly used interior protocol that selects the route with the lowest metric (hop count) as the best route.
Open Shortest Path First (OSPF) Version 2 RFC 1583 Another interior routing protocol, OSPF is a link-state protocol (shortest path first) and better suited than RIP for use in complex networks with many routers.
Exterior Gateway Protocol (EGP) RFC 904 EGP exchanges reachability information between autonomous systems. An autonomous system is usually defined as a set of routers under a single administration, using an interior gateway protocol and common metric to route packets. Autonomous systems use exterior routing protocols to route packets to other autonomous systems.
Border Gateway Protocol (BGP) RFCs 1163, 1267, 1771 Like EGP, BGP exchanges reachability information between autonomous systems but supports nonhierarchical topologies. BGP uses path attributes to provide more information about each route. Path attributes can include, for example, administrative preferences based on political, organizational, or security considerations.
Router Discovery RFC 1256 This protocol is used to inform hosts of the availability of routers that it can send packets to, and to supplement a statically configured default router.

These routing protocols are configured in the GATED configuration file TCPIP$GATED.CONF. This file contains statements that control tracing options, select routing protocols, manage routing information, and manage independent system routing.

For information on configuring dynamic routing with GATED, see Section 4.4.

4.2 Configuring Static Routes

The first time you run the configuration procedure, TCPIP$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$COMMON:[SYSEXE]TCPIP$ROUTE.DAT. To specify a different name, define the systemwide logical name TCPIP$ROUTE.


Do not enter the CREATE ROUTE command unless you intend to reconfigure your entire cluster.

4.2.1 Creating a Default Route

When TCP/IP is sending a packet, it consults the routing table to determine which interface is connected to the destination network. If the packet has a destination network address that is unknown, the packet is sent to the default router. The default route points at the default router. For example, if a router with address is designated to route all packets between the local network and the rest of the world, then the default route can be set with the following command:


If TCP/IP Services is active, this affects the active routes database. To ensure this default route is available next time TCP/IP Services is started, the /PERMANENT qualifier must be used. For example:


Use the SET NOROUTE command to remove a route.

Or you can define the default route using the route UNIX command. In this case, to ensure the default route is recreated next time TCP/IP Services is started, add the command to SYS$STARTUP:TCPIP$SYSTARTUP.COM. For example, to create the same default route as defined above, use the following UNIX style command:

$ route add default 

To remove the route, enter the following command:

$ route delete default 

4.2.2 Manually Defining Static Routes

To create a static route, use the SET ROUTE command. The command has the following effects:

The SET ROUTE command requires the following information:

HP strongly recommends that you do not specify alias names with the destination parameter or the /GATEWAY=host qualifier.

To define a route to any host on a specific network, enter:

TCPIP> SET ROUTE network_IP_address /GATEWAY="gateway" /NETWORK 

To define a route to a specific host on a specific network, enter:

TCPIP> SET ROUTE remote_host /GATEWAY="gateway" Examples

  1. In the following example, the network is active. The SET ROUTE command adds a route to the volatile routes database. TCPIP starts directing communication for flamingo through gateway francolin .

    TCPIP> SET ROUTE "flamingo" /GATEWAY="francolin" 

  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 uses gateway francolin .


  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 the product starts up, packets for NENE will go through a gateway called bird.of.paradise .

    TCPIP> SET ROUTE NENE /GATEWAY="bird.of.paradise" 

    At startup, the information in the permanent routes database, if any exists, is loaded into the volatile routes database. You can add permanent routes while the product is stopped or while it is running. If it is running, use the /PERMANENT qualifier.

  4. The following command permanently sets routing for host albatross to go through gateway birdygate .

    TCPIP> SET ROUTE "albatross" /GATEWAY="birdygate" /PERMANENT 

    A default route is a route used to direct data that is addressed to an unidentifiable network address. To define a default route, use the /DEFAULT qualifier.

  5. The following command sets a default route. NIGHTINGALE is the default gateway.


    To check that your routes are set up correctly, use either the LOOP or PING command.

4.2.3 Displaying Manually Defined Routes

To display static routes, use the SHOW ROUTE command. To see the permanent database, specify the /PERMANENT qualifier.

The display shows the following types of routes:

To display a route that was defined by an address, specify either its address or a wildcard.

Some examples of displaying routes are listed below.

  1. The following example displays information about all the manually defined routes.

    Type           Destination               Gateway 
    AN   destin_host1   gate_host 
    AH  destin_host2   gate_host_2 

  2. The following example displays the permanent static routes that were defined with SET ROUTE/PERMANENT.

    Type           Destination               Gateway 
    PN              pterodactyl.extinct.com 

Another way to display route information is by using the netstat UNIX command. For example, to display the routes, and suppress conversion of network numbers to names, enter the following commands:

$ netstat -rn 
Routing tables 
Destination      Gateway            Flags     Refs     Use  Interface 
Route Tree for Protocol Family 26: 
Route Tree for Protocol Family 2: 
default        UG          0        0  WE1 
default        UG          0        0  WE0 
16.20/16      U           2       56  WE1 
16.20/16      U           1        9  WE0      UHL         0        0  WE0      UHL         0        0  WE1          UHL         1        1  LO0 

This example shows a multihomed host with two interface adapters. For more information about the netstat utility, enter the following command:


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