Understanding LAN Failover

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HP OpenVMS System Manager's Manual, Volume 2:...

Managing the Local Area Network (LAN) Software

Managing the LAN MOP Downline Load Service

Managing InfoServer Systems

Understanding LAN Failover

LAN Failover is a mechanism for protecting your system from a LAN device failure. LAN Failover does this by integrating multiple LAN devices into a single virtual interface, called a LAN Failover set.

A failover set consists of one active LAN device and a number of inactive LAN devices. If the active adapter fails, transmit and receive operations transfer automatically and transparently to one of the inactive devices. You can create a failover set with just one LAN device, although failover will not occur until an additional device is added to the set.

Software: Logical LAN Driver

The Logical LAN driver, SYS$LLDRIVER.EXE, implements LAN failover by managing the operation of the LAN Failover set and channelling I/O requests to the active LAN device driver. When the active LAN device fails, LLDRIVER switches to another LAN device, selecting it according to its assigned priority and its link state.

Hardware: Logical LAN Device

A logical LAN device, LLc0, is created for each LAN Failover Set (where c is a user-specified alphabetic character uniquely identifying the logical LAN device). This is a pseudo LAN device or virtual LAN device. Applications direct I/O requests to the logical LAN device. The Logical LAN driver channels these requests to the active LAN device.

Software - LAN Failover Management

The system manager defines and creates a LAN Failover set using the LANCP and LANACP utilities. LAN Failover set context is maintained in the permanent LAN device database. At system startup and when LANACP is restarted, LANACP reads the permanent device database and sets up any LAN Failover set described in the database.

During system operation, you can look at failover status and configuration data. You can also change the characteristics of a failover set, both in the permanent device database and its current instantiation as maintained in the volatile device database.

Network Configuration and Hardware Requirements

LAN Failover requires that the LAN devices in the failover set be on the same extended LAN. This requirement ensures that LAN communications between arbitrary nodes can continue after a failover event.The LAN devices that support LAN Failover are the DE500-BA, DE504-BA, DE600, and variants on Alpha systems; the Intel 82559, A5230A, and A5506B on I64 systems; and all Gigabit devices on Alpha and I64 systems. The embedded Intel 82559 chip on the AlphaServer DS25 is supported as well.

Detecting Network Connectivity Failures

Typically, a LAN device is connected to a network switch. The state of the connection is described as either 'link up' or 'link down'. A 'link up' condition means there is a valid connection from the LAN device to the switch that allows transmission of network data between the LAN device and the switch. A 'link down' condition means there is no valid connection, either because the cable has failed or been disconnected, or because one side of the connection has failed. If the switch is powered off or reset, the link is 'down' until the switch is running again. If the LAN device is reset, the link is 'down' until the LAN driver has completed reset and the LAN device has been reinitialized.

LAN Failover protects against failure of the LAN device, the cable connecting it to the switch, and failure of the switch. LAN Failover does not protect against failures beyond the switch, that is, failure of parts of the LAN that are not visible to the LAN devices in the failover set.Each LAN device in a failover set monitors the link state and reports the state of the link to LLDRIVER. LLDRIVER tracks the link state and performs a failover when the active LAN device reports a 'link down' condition.

LAN Failover Restrictions

Restrictions for LAN Failover are the following:

LAN Failover is not supported on cluster satellites.

Point-to-point connections are not supported. In a point-to-point configuration containing more than the LAN devices, LLDRIVER cannot guarantee that the same point-to-point device is selected as the next active device after a failure. For configurations with just two LAN devices, there is sufficient variability in link state timing that predictable operation of the failover set cannot be assured.

Failures beyond the scope of the LAN device and its connection to the switch cannot be detected.

When jumbo frames are enabled, all LAN devices in the failover set must support jumbo frames, and the network infrastructure must also be set up accordingly. For example, if the path from one LAN device to another node supports jumbo frames, the paths from all other LAN devices in the failover set to the same node must also support jumbo frames.

Managing LAN Failover

The LAN volatile and permanent device databases contain an entry for each LAN device that exists on the system. The logical LAN device LLc is added to these databases through LANCP and LANACP when the system manager creates a LAN Failover Set.To enter the LLc device into the LAN permanent device database or to modify an existing entry, enter the LANCP command DEFINE DEVICE LLc using the following syntax:DEFINE DEVICE LLc[/qualifiers]

This command allows the settings to take effect on subsequent boots.

To enter the LLc device into the LAN volatile device database or to modify an existing failover set, enter the LANCP command SET DEVICE LLc using the following syntax;SET DEVICE LLc[/qualifiers]

This command changes the settings immediately.The LAN device priority is managed on the LAN devices individually, rather than on the logical LAN device.

Creating a LAN Failover Set

The logical LAN device is created when you create a LAN Failover set. To create a LAN Failover set, enter the LANCP command SET DEVICE LLc using the following syntax:SET DEVICE LLc/FAILOVER_SET=(device-name[,...])

In this command, supply the LAN physical device name for the device-name; for example:

LANCP> SET DEVICE LLA/FAILOVER_SET=(EWA,EIA,EWB)

This command fails if any specified LAN devices have active users. You can show any active users by entering the LANCP command SHOW CONFIG/USERS. Note that users are channels assigned to the device by an application. One application can assign multiple channels.You can also use LANCP DEFINE DEVICE commands to set up a failover set in the LAN permanent device database. When the system boots, the failover set is initialized before any users (applications) are started. If LANACP is stopped and restarted, LANACP attempts to set up any failover sets defined in the LAN permanent device database. In this case, you must stop any existing users so that LANACP can successfully set up a failover set.

Adding a Device to a LAN Failover Set

You can add LAN devices to an existing failover set by specifying additional LAN devices; for example, to add EWC to the failover set above, enter the following command:

LANCP> SET DEVICE LLA/FAILOVER_SET=EWC

Removing a Device from a LAN Failover Set

To delete a device from a LAN Failover set, enter the LANCP command SET DEVICE using the following syntax:SET DEVICE LLc/NOFAILOVER_SET=(device_name[,...])

In this command, supply the LAN device name to be removed; for example:

LANCP> SET DEVICE LLA/NOFAILOVER_SET=EWB

This command fails if one of the specified devices is the active LAN device.

Enabling a LAN Failover Set

Enabling a LAN Failover set activates it. LLDRIVER selects one of the LAN devices according to priority and link state, and allows I/O from users to the logical LAN device.To enable a LAN Failover Set, enter the LANCP command SET DEVICE using the following syntax:SET DEVICE LLc/ENABLE

Disabling a LAN Failover Set

Disabling a LAN Failover set deactivates the logical LAN device. When the logical LAN device is deactivated, user I/O requests are completed with error status. When disabled, LAN devices can be added and removed from the failover set.Note that a LAN device can be removed from an enabled LAN Failover Set, as long as the device is not the active device. A device can be added as long as it has no active users.To disable a LAN Failover set, enter the LANCP command SET DEVICE using the following syntax:SET DEVICE LLc/DISABLE

This command fails if the logical LAN device has active users.

Setting the Priority of a LAN Failover Device

To give preference to a physical LAN device when LLDRIVER selects the active LAN device for a LAN Failover Set, enter the LANCP command SET DEVICE/PRIORITY using the following syntax:SET DEVICE device-name/PRIORITY=value

In this command, supply the LAN device name for the device-name and an integer for the value parameter; for example:

LANCP> SET DEVICE EIA/PRIORITY=20

When selecting the active participant, LLDRIVER selects the device with the highest priority that is in the 'link up' state.

Setting the Packet Size of a LAN Failover Set

The default maximum packet size of a LAN Failover set is the standard Ethernet maximum packet size of 1518 bytes. When all LAN devices in the failover set support jumbo frames, you can enable use of jumbo frames to select the standard Ethernet maximum packet size or the jumbo packet size. To do so, enter the LANCP SET DEVICE/SIZE command using the following syntax:

SET DEVICE LLc/SIZE=STANDARD

SET DEVICE LLc/SIZE=JUMBO

Note that the LAN_FLAGS system parameter is usually used to enable the use of jumbo frames on Gigabit LAN devices. Alternatively, you can enable or disable jumbo frames on specific devices using the LANCP command SET DEVICE/[NO]JUMBO. The size selection for the logical LAN device overrides the jumbo setting of the LAN devices in the failover set. The setting can be changed when the failover set is in the disabled state.

Displaying LAN Failover Characteristics

To display LAN Failover status, enter the LANCP command SHOW DEVICE LLc using the following syntax:SHOW DEVICE LLc/CHARACTERISTICS

The display shows the characteristics that are specific to LAN Failover for a particular node, as shown in the following example:

Device Characteristics LLAO:

Value   Characteristic
             . . .

          Disabled  Jumbo frames
         "EIA"      Failover device (active)
         "EWA"      Failover device
 
    Enabled/Active  Logical LAN state
                 0  Failover priority

Displaying LAN Failover Counters

LLDRIVER redirects I/O requests from the logical LAN device to the active LAN device. The LANCP commands to display device counters or driver internal counters are redirected to the active LAN device.

Validating a LAN Failover Set

The network devices associated with a LAN Failover set must provide physically redundant paths on the same local network for LAN Failover to function correctly. Since networks are usually stable, the active member of a LAN Failover set might not change often. However, when the active member does change, it is crucial that the idle NICs have been set up properly. The system manager can validate each member of the failover set by simulating LAN failures using the LANCP qualifier /SWITCH. The /SWITCH qualifier simulates a network failure on the active device and selects another device from the failover set to be the active device.

To simulate a LAN failure, enter the LANCP command SET DEVICE LLc using the following syntax:

SET DEVICE LLc/SWITCH

Illustration of LAN Failover

LAN Failover illustrates LAN Failover.

Figure 1 LAN Failover

Managing the LAN MOP Downline Load Service

Managing InfoServer Systems