Faking broadcast capability

SUSE Linux Enterprise Server 15 SP5 LPAR mode z/VM guest

It is possible to fake the broadcast capability for devices that do not support broadcasting.

Before you begin

You can fake the broadcast capability only on devices that do not support broadcast.
The device must be offline while you enable faking broadcasts.

About this task

For devices that support broadcast, the broadcast capability is enabled automatically.

To find out whether a device supports broadcasting, use the ip command. If the resulting list shows the BROADCAST flag, the device supports broadcast. This example shows that the device eth0 supports broadcast:

# ip -s link show dev eth0
3: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1492 qdisc pfifo_fast qlen 1000
    link/ether 00:11:25:bd:da:66 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast
    236350     2974     0       0       0       9
    TX: bytes  packets  errors  dropped carrier collsns
    374443     1791     0       0       0       0

Some processes, for example, the gated routing daemon, require the devices' broadcast capable flag to be set in the Linux® network stack.

Procedure

To set the broadcast capable flag for devices that do not support broadcast, set the fake_broadcast attribute of the qeth group device to 1. To reset the flag, set it to 0.

Issue a command of the form:

# chzdev <device_bus_id> fake_broadcast=<flag>

This setting persists across re-boots. For more details, see Persistent device configuration.

To apply this setting to the running system only, use the chzdev command with the -a option or the sysfs attribute fake_broadcast:

# echo <flag> > /sys/bus/ccwgroup/drivers/qeth/<device_bus_id>/fake_broadcast

Example

In this example, a device 0.0.a100 is instructed to pretend that it can broadcast.

# chzdev 0.0.a100 fake_broadcast=1

Or, for the running configuration using sysfs:

# echo 1 > /sys/bus/ccwgroup/drivers/qeth/0.0.a100/fake_broadcast