Activating an interface

Red Hat Enterprise Linux 8.6 LPAR mode z/VM guest

Use the ip command or equivalent to activate an interface.

Before you begin

You must know the interface name of the qeth group device.
You must know the IP address that you want to assign to the device.

About this task

The MTU size defaults to the correct settings for HiperSockets devices. For OSA-Express CHPIDs in QDIO mode, the default MTU size depends on the device mode, layer 2 or layer 3.

For layer 2, the default MTU is 1500 bytes.
For layer 3, the default MTU is 1492 bytes.

In most cases, the default MTU sizes are well suited for OSA-Express CHPIDs in QDIO mode. If your network is laid out for jumbo frames, increase the MTU size to a maximum of 9000 bytes for layer 2, or to 8992 bytes for layer 3. Exceeding the defaults for regular frames or the maximum frame sizes for jumbo frames might cause performance degradation. See Open Systems Adapter-Express Customer's Guide and Reference, SA22-7935 for more details about MTU size.

For HiperSockets, the maximum MTU size is restricted by the maximum frame size as announced by the Licensed Internal Code (LIC). The maximum MTU is equal to the frame size minus 8 KB. Hence, the possible frame sizes of 16 KB, 24 KB, 40 KB, or 64 KB result in maximum corresponding MTU sizes of 8 KB, 16 KB, 32 KB, or 56 KB.

The MTU size defaults to the correct settings for both HiperSockets and OSA-Express CHPIDs in QDIO mode. As a result, you do not need to specify the MTU size when you activate the interface.

Procedure

You activate or deactivate network devices with ip or an equivalent command. For details of the ip command, see the ip man page.

Examples

This example activates a HiperSockets CHPID with broadcast address 192.168.100.255:
```
# ip addr add 192.168.100.10/24 dev enca1c0
# ip link set dev enca1c0 up
```
This example activates an OSA-Express CHPID in QDIO mode with broadcast address 192.168.100.255:
```
# ip addr add 192.168.100.11/24 dev encf500
# ip link set dev encf500 up
```
This example reactivates an interface that was already activated and subsequently deactivated:
```
# ip link set dev encf500 up
```