DIGITAL TCP/IP Services for OpenVMS

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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. Enter the DCL SET TERMINAL command.

3.3.7 Troubleshooting SLIP

See Section A.10.

Chapter 4
Configuring Routing

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 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 information about routes in routing tables. With DIGITAL TCP/IP Services for OpenVMS, 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 on the changes.

Routing daemons implement a routing policy, that is, the set of rules that decide 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.

DIGITAL TCP/IP Services for OpenVMS 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-de) 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 1388 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, 1654 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 hosts 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 execute the CREATE ROUTE command unless you intend to reconfigure your entire cluster. Manually Defining Routes (Static Routes)

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

The command requires the following information:

Compaq 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" 

Example 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" 

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 use 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 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.

Example 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.

Example 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. 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 address, specify either its address or a wildcard.

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

                             DYNAMIC database 
Type           Destination               Gateway 
AN   destin_host1   gate_host 
AH  destin_host2   gate_host_2 

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

Type           Destination               Gateway 

4.3 Enabling and Disabling Dynamic Routing

Use the configuration procedure TCPIP$CONFIG to enable dynamic routing and configure your host to receive routing protocol messages as follows:

  1. Select the "Routing" option from the CORE ENVIRONMENT menu.
  2. Answer "Yes" to the question "Do you want to reconfigure dynamic ROUTED or GATED routing [NO]:"
  3. If you choose to enable ROUTED, indicate whether you want your host to supply RIP updates to other hosts on the network (in addition to receiving RIP updates) and the default network route.
  4. If you choose to enable GATED, you must also configure the routing protocols in the GATED configuration file TCPIP$GATED.CONF. See Section 4.4 for more information about configuring GATED.

To disable dynamic routing:

  1. Select the "Routing" option from the CORE ENVIRONMENT menu.
  2. Answer "Yes" to the question "Do you want to enable GATED routing configuration [NO]:" or enter the command STOP ROUTING.

When you disable GATED routing, the GATED routes are preserved. To disable GATED and remove all GATED routes from the routing table, enter the command STOP ROUTING/GATED.

4.4 Configuring GATED

You must configure the GATED protocols before enabling GATED routing. Edit a copy of the sample file TCPIP$GATED.TEMPLATE (located in SYS$SYSDEVICE:[TCPIP$GATED]) to add statements that select routing protocols, manage routing information, manage independent system routing, and control tracing options.

After editing this file, save it to TCPIP$GATED.CONF, in SYS$SYSDEVICE:[TCPIP$GATED], and use TCPIP$CONFIG to enable GATED. If GATED is already running, you must stop it by entering the command STOP ROUTING/GATED then restart GATED (enter START ROUTING/GATED.)

If you do not format the configuration file correctly, GATED will terminate.

See DIGITAL TCP/IP Services for OpenVMS Management Command Reference for detailed descriptions of the SET GATED and START ROUTING/GATED commands.

4.4.1 Sample GATED Configuation File

A sample GATED configuration file follows. For a description of valid statements, statement syntax, and sample protocol configurations, see Appendix B.

#           Copyright (c) Digital Equipment Corporation, 1998 
#        TCPIP$GATED.CONF - Sample gateway routing daemon (GATED) 
#          configuration file, preconfigured for RIP v1. 
#   This file contains information that is read by the GATED daemon at 
#   initialization time.  This file contains statements that 
#    o  Control tracing options 
#    o  Select routing  protocols 
#    o  Manage routing information 
#    o  Manage idependent  system routing 
#   See the DIGITAL TCP/IP Services for OpenVMS Management guide for 
#   instructions on using this file. 
interfaces { 
        interface all passive ; 
# Protocols: 
rip on { 
        interface all ripin ripout version 1; 
redirect on; 
routerdiscovery server off; 
hello off; 
ospf off; 
egp off; 
bgp off; 
snmp off; 
# Static routes: 
#static { 
# mask gateway; 
#       default gateway; 
#       }; 
# Policy: 
#export proto rip { 
#       proto static { all metric 1; }; 
#       proto direct { all; }; 
#       proto rip { all; }; 
#       }; 

4.5 Configuring the Gateway Function (IP Forwarding)

By default, the startup procedure automatically sets IP forwarding.

To manually configure your system as an internet gateway, enter the following commands:

Identify the gateway for each client. For instructions, see the client's product documentation.

To disable the gateway function interactively, enter:


To disable the gateway at TCP/IP Services startup, type:


4.5.1 Datagram Reassembly Time

Reassembly is the process of reconstructing a complete data message from received fragments. The reassembly timer determines the length of time allowed for the reassembly process. You can modify the reassembly timer to ensure that IP datagram fragments are optimally reassembled at the destination host.

Consider the following when setting the reassembly timer:

Enter the following commands to reset the reassembly timer:

In the following example, the first command changes the IP reassembly time to 20 seconds on the running system. This new setting remains in effect until the next TCP/IP Services startup.

The second command makes the change permanent by modifying the configuration database, TCPIP$CONFIGURATION.DAT.


4.6 Subnetwork Routing

Subnetwork routing, also called subnetting, lets you extend the IP addressing scheme by organizing hosts within a network into logical groups. A network can be made up of several subnetworks.

If a gateway connects these networks, a host on another network can access a host on a subnetwork. Data from the host on the other network is routed as follows:

Subnetwork routing lets one network address span multiple physical networks. You can use local gateways and subnetwork addresses to each local physical network to make your network appear as one network to other systems.

For example, a company has one assigned IP address, even though it has several physical networks. Using local gateways, the network manager assigns a subnetwork address to each local physical network. This makes the company appear to have only one network to outside systems.

Subnetwork routing also works in the reverse. You can create multiple subnetworks (logical groups) on the same physical network. Use a network interface as a gateway between the multiple subnetworks. Setting up multiple subnets on one physical network has one disadvantage. Because the subnetworks are on the same broadcast medium, they receive broadcasts destined for other subnetworks, and these broadcasts must be discarded, except on the gateway.

4.6.1 Extending Subnetwork Routing

To use extended subnetwork routing, define pseudo-interfaces. A pseudo-interface is a data structure that extends subnetwork routing. The name of an internet pseudo-interface has the following characteristics:

For example, for an OpenVMS Alpha system with two Ethernet controllers --- EZA0 and EZB0 --- you can define the following internet interfaces and pseudo-interfaces:

To extend subnetwork routing, follow these steps:

  1. Define the pseudo-interfaces. Use the SET INTERFACE and SET CONFIGURATION INTERFACE commands. Enter:

    TCPIP> SET INTERFACE interface /HOST=host - 

    For example, to specify the pseudo-interface FFA0 on host KESTREL, with network mask and broadcast mask to, enter:


  2. Enter the same information into the configuration database to set up the interfaces at startup. Enter:


    To display information about the network interfaces, use the SHOW INTERFACE command.

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