Chapter 8 - Managing IP Interfaces and ARP Entries
This chapter discusses the Managing IP Interfaces menu. From this menu, you can perform the following tasks:
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Assign IP addresses to either a physical LAN interface or the logical VINES interface. The IP Interfaces Worksheet, discussed in Chapter 4, tells which interfaces you have to add, and the parameters they require. ![]()
Establish Address Resolution Protocol (ARP) dialogues with other machines in your network that implement ARP. The ARP Entries Worksheet, also discussed in Chapter 4, tells which interfaces require you to create ARP entries, or to enable or disable ARP.
If you are modifying IP interface definitions or ARP entries, carefully consider the modifications you plan to make. Refer to Chapter 2 and Chapter 4 if you need more information.
Throughout this chapter, information on the sample IP Interfaces Worksheet and the sample ARP Entries Worksheet in Chapter 4 is used in examples. These worksheets are repeated in Figures 8-1 and 8-2.
Accessing IP Interface Management Functions
The Manage Network Interfaces menu allows you to perform all IP interface management functions. To display this menu, choose Manage Network Interfaces from the TCP/IP main menu (see Chapter 7).
The menu displays entries for all the interfaces that have been added to the TCP/IP configuration. Each entry contains the following fields:
Interface - The name of the interface.
St - The interface's status. This field displays E if the interface is enabled, D if the interface was manually disabled, or SD if the system tried unsuccessfully to enable the interface (that is, if the interface was disabled because of a system failure, or if the server could not find the LAN card when it was booted). If defined, the VINES interface is always enabled.
Slt - The number of the slot in which the interface's LAN card resides. This field does not apply to the VINES interface.
IP address - The IP address assigned to the interface.
Subnetwork mask - The subnetwork mask specified for the interface's IP address.
Broadcast addr - The broadcast/destination address of the interface, which is used to send broadcasts over the attached physical medium. Typically, the address consists of the network and subnetwork number (if subnetting is used) in the IP address of the interface, and a host field in which the bits are either all zeros or all ones. This field does not apply to the VINES interface.
The functions you can perform from the menu are described in the sections that follow.
This section describes the following topics:
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Adding an IP interface ![]()
Modifying an IP interface ![]()
Deleting an IP Interface
The screens discussed in these sections are accessed from the Manage Network Interfaces menu.
When you add an IP interface, assign it an IP address and a subnetwork mask that defines the number of bits to be used for the network and subnetwork field.
You should complete an IP Interfaces Worksheet before adding interfaces.
To add an interface, follow these steps:
1. Choose ADD an interface.
2. At the next menu, choose a LAN card or the VINES interface.
Note: The VINES interface is available only if the Banyan Routing option is installed on your server.
3. If you choose the VINES interface, the configuration program prompts you to confirm your decision. You should choose the VINES interface only if workstations use VINES to route IP traffic to your server. These workstations need the VINES Transport version of FTP Software, Inc.'s PC/TCP. Choose YES to continue. Choose NO to cancel the addition.
4. At the IP Interface Address screen, assign an IP address to the selected interface. Using the sample worksheet in Figure 8-1, you would assign 160.134.1.1 to the first EtherLink interface.
5. At the Specify Subnetwork Mask screen, specify the subnetwork mask for the IP address. Use the default if the IP address is not subnetted. Using the sample worksheet, you would specify 255.255.255.0 for the IP address you assigned to the first EtherLink interface.
6. At the next screen, specify whether you want the interface to be enabled. YES is the default.
Caution: If you specify an IP network address with no subnetwork mask, routes elsewhere in your network will not be usable if they meet the following criteria:
- They have the same network number as the network you established.
- They use a subnetwork mask.
When you complete all steps, the interface is added to the TCP/IP configuration. The interface definition appears on the Manage Network Interfaces menu.
Before you modify any of the parameters that make up an IP interface, carefully consider whether your changes will adversely affect communications between your server and other hosts. For example, if you modify the network or subnetwork part of an IP address, any routes that the configuration program created using those numbers are modified as well.
When you modify an IP interface definition, the configuration program steps you through the same series of screens that were used to add the interface. Follow these steps:
1. At the Manage Network Interfaces menu, choose Modify an Interface.
2. Choose the interface you wish to modify. You then display the screens containing interface information. See the preceding section, "Adding an Interface," if you need information.
3. Modify the interface information.
4. After modifying information, return to the Manage Network Interfaces menu, which shows the new information you have entered for the interface.
Caution: If you specify an IP network address with no subnetwork mask, routes elsewhere in your network will not be usable if they meet the following criteria:
- They have the same network number as the network you established.
- They use a subnetwork mask.
To delete an IP interface, follow these steps:
Note: Deleting an IP interface removes the interface, as well as the ARP entries, adjacent networks, and routing entries associated with it, from the TCP/IP configuration.
1. At the Manage Network Interfaces menu, choose DELETE an Interface.
2. Choose the interface you wish to delete.
3. The configuration program prompts you for confirmation. Specify YES to delete the interface, or NO to cancel the deletion. YES is the default.
Enabling and Disabling an Interface
This function allows you to enable and disable IP interfaces. Follow these steps:
1. At the Manage Network Interfaces menu, choose ENABLE/DISABLE an interface.
2. Choose an interface from the list on the screen.
3. The configuration program asks you to confirm your decision. Specify YES or NO. (YES is the default.) For example, if the interface is enabled, specify YES to disable the interface, or NO to keep the interface enabled.
Note: If you disable an interface, any routes, ARP entries, and adjacent networks configured for that interface will be deleted by the system.
Changing an IP Broadcast Address
If the default IP broadcast address assigned by the configuration program does not match the address on the IP interfaces Worksheet, you should change the value in the configuration program. Chapter 4 discusses how to determine the IP broadcast address for an interface.
If you must change the IP broadcast address, follow these steps:
1. At the Manage Network Interfaces menu, choose CHANGE Broadcast Address.
2. Choose the interface for which you are changing the IP broadcast address.
3. At the next screen, enter the new IP broadcast address.
Address Resolution Protocol Management Tasks
This section discusses the following topics:
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The Manage ARP Entries Menu ![]()
Adding an Entry ![]()
Modifying an Entry ![]()
Deleting an Entry ![]()
Displaying System ARP Entries ![]()
Enabling and Disabling ARP ![]()
Enabling and Disabling Direct Mapping
Make sure that you have your ARP Entries Worksheet available for any interface whose ARP entries you need to manage. Refer to Chapter 2 for information on ARP, and Chapter 4 for information on filling out the ARP Entries Worksheet.
The Manage ARP Entries Menu allows you to perform all Address Resolution Protocol management functions for a particular LAN interface. To display the Manage ARP Entries menu, follow these steps:
1. At the Manage Network Interfaces menu, choose MANAGE ARP Entries.
2. Select the LAN interface for which you are managing ARP entries.
The Manage ARP Entries menu tells you whether ARP is enabled, and whether direct mapping is enabled. The menu lists all the ARP entries that are permanent, and those that are both permanent and published. Each entry contains the following fields:
IP Address - The IP address of the host.
LAN Address - The LAN address of the host.
Type - The entry type: Permanent (manually configured) or, if the entry is both permanent and published, perm/publish.
Status - The status of the entry: in use if the interface is enabled, or NOT in use.
The functions you can perform from the Manage ARP Entries menu are explained in the sections that follow.
When you add an ARP entry, specify an IP address/LAN address pair. You must also specify whether the entry is permanent or both permanent and published. See Chapter 4 for more information on permanent (manually configured) and published ARP entries.
You should complete an ARP Entries Worksheet before adding an ARP entry. This worksheet is discussed in Chapter 4.
To add an ARP entry, follow these steps:
1. At the Manage ARP Entries menu, choose ADD an Entry.
2. At the CONFIGURE an ARP Entry screen, specify the IP address of a host on the LAN and its LAN address. Using the sample worksheet in Figure 8-2, you would assign 160.134.2.2 as the IP address and 02608c313416 as the LAN address for a host on Ethernet.
3. At the next screen, the configuration program asks whether the entry should be published. Specify NO (the default) to make the entry permanent. Specify YES to make the entry both permanent and published. Also, specify YES if your server is implementing proxy ARP.
4. When you complete all steps, the Manage ARP Entries menu appears. It displays the ARP entry you just created, as well as entries that were added previously.
When you modify an entry, the configuration program steps you through the same series of screens that were used to add the entry. Follow these steps:
1. At the Manage ARP Entries menu, choose MODIFY an Entry.
2. Choose the entry you wish to modify. Display the screens that contain information on the entry, and modify the information accordingly. See the preceding section, "Adding an ARP Entry," for more information.
3. After modifying the information, return to the Manage ARP Entries menu. The menu shows the new information you entered.
Manually configured ARP transactions are displayed on the Manage ARP Entries menu. Your system also performs other ARP transactions that do not appear on the Manage ARP entries menu. All ARP transactions in progress, whether manually configured or automatic, are displayed on the Display System ARP Entries screen. To see this screen, choose Display System ARP Entries at the Manage ARP Entries menu.
You should use this function whenever you want to check the status of ARP entries for a particular interface. This is useful if you are troubleshooting problems in your network.
This screen shows the IP addresses known by the server, and the physical LAN addresses associated with those IP addresses. The following fields appear on the screen:
IP Address - The IP address of a destination reachable from this server through IP.
Link Address - The physical LAN address of the destination.
Status Flags - The status of the ARP transaction. Table 8-1 summarizes the status flags field.
Entries that are not manually configured are temporary entries. Temporary ARP entries are flushed from the ARP cache if they are not used after a certain period of time. For example, use of an entry stops, and the entry is eventually deleted, when a host associated with the entry is removed from the LAN.
An entry is updated if the host with which it is associated reappears on the LAN and is assigned a different IP address. In this event, the old entry contains the wrong IP address/Link address pair, and is updated. If an update occurs while you are displaying the screen, you must press F9 to see the updated status.
To delete an entry, perform the following steps:
1. At the Manage ARP Entries menu, choose DELETE an Entry.
2. Choose the entry.
3. The configuration program prompts you for confirmation. Specify YES if you want to delete the entry, or NO if you want to cancel the deletion. YES is the default.
ARP is enabled by default, except for ProNET-10 LANs where direct mapping is enabled. However, you may want to disable ARP in situations such as the following:
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Many of the hosts to which your server is connected on a LAN do not support ARP. You want to disable ARP to stop unnecessary traffic. ![]()
ARP does not correctly match IP addresses and LAN addresses. You want to disable ARP and begin troubleshooting the problem.
The Manage ARP Entries menu tells you whether ARP is enabled or disabled. To change the status, follow these steps:
1. At the Manage ARP Entries menu, choose ENABLE/DISABLE ARP.
2. The configuration program asks you to confirm your decision to enable or disable ARP. Specify YES or NO. YES is the default. For example, if ARP is enabled, specify YES to disable it, or NO to keep it enabled.
Caution: Disabling Direct Mapping does not enable ARP automatically.
Enabling and Disabling Direct Mapping
This function applies only to ProNET-10 LANs. If you enable direct mapping, ARP is disabled automatically.
The Manage ARP entries menu tells you whether direct mapping is enabled or disabled. To change the status, perform the following steps:
1. At the Manage ARP Entries menu, choose ENABLE/DISABLE Direct Mapping.
2. The configuration program asks you to confirm your decision. Specify YES or NO. YES is the default. For example, if direct mapping is enabled, specify YES to disable it, or NO to keep it enabled.