IFCONFIG Command

Command Options

Notes:

¹ Each option or operand can be entered only once.
² The dash (–) is required at the beginning of each command option.

Interface Operands

Notes:

¹ This operand can be used to change previously defined devices.
² For virtual devices coupling to an existing guest LAN or VSWITCH, the default is the transport type of that guest LAN or VSWITCH.
³ PATHMTU is the default when the PATHMTU operand is specified on the ASSORTEDPARMS statement in the TCP/IP configuration file. Otherwise, NOPATHMTU is the default.

Interface Operands Continued

Purpose

Use the IFCONFIG command to configure network interfaces for the z/VM TCP/IP stack or to display the current configuration. It may be used instead of, or in conjunction with, the existing NETSTAT and OBEYFILE commands.

IFCONFIG does not make permanent changes to the network configuration, but it can provide data for this purpose that is compatible with the TCP/IP server configuration file.

Options

-All

Displays the status of all TCP/IP interfaces.

-DEBUG

Provides information for diagnosing problems associated with the use of this command, in consultation with the IBM® TCP/IP support group.

-Force

Bypasses the device consistency verification logic that is used by IFCONFIG when a new device is defined. The device is added to the z/VM TCP/IP configuration.

-Help

-?

Provides help information about the IFCONFIG command. You cannot specify the HELP parameter on the IFCONFIG command line with other parameters.

-Mdiskpw password

Specifies the read password, if required, of the first read/write minidisk on which an obey file generated by IFCONFIG is to reside. IFCONFIG uses the OBEYFILE command to facilitate network interface configuration changes, and in so doing creates a temporary obey file for this purpose.

-Remove

Removes the interface from the configuration. The option detaches a real device or destroys a virtual device. The interface must be inactive before -Remove is specified.

Note: -Remove cannot be specified with any command operands.

-Show

Displays the TCP/IP server configuration file statements that are required to change an existing or define a new interface, but does not change the running system. These statements are device-specific and limited in scope. Before using this information to apply permanent changes to the TCP/IP server configuration, ensure that all of the necessary data for a given statement is provided.

If no interface is specified with the -Show option, then information about all known, active interfaces is displayed.

-TCP userid

Applies this instance of the IFCONFIG command to a specific z/VM TCP/IP stack virtual machine. The IFCONFIG command communicates with the TCP/IP stack identified by any one of the following:

The user ID specified with the -TCP option
The TCPIPID C environment variable (established via the command):
```
GLOBALV SELECT CENV SETL TCPIPID userid
```
The TcpipUserid value from the TCPIP DATA file
User TCPIP

-Verbose

Displays any CP or NETSTAT commands that are used while changing the running system. To obtain a complete picture of what commands and TCP/IP configuration file statements are required to manually configure z/VM TCP/IP, the -Verbose option can be combined with the -Show option, but then no changes are made to the running system.

Operands

interface

Specifies the name of a network interface assigned to a particular TCP/IP virtual machine. This interface name is limited to 16 characters and cannot begin with a dash (-), end with a colon (:), or contain a semicolon (;).

The interface name corresponds to the link name that is defined on a LINK statement in PROFILE TCPIP.

ipv4_address

The primary IPv4 address of the interface.

masklength

The number of bits used to represent the subnet mask of the interface.

Example: 192.168.0.12/24 would indicate a subnet mask of 255.255.255.0
is to be used with an IPv4 address of 192.168.0.12.

If the ipv4_address/masklength format is used rather than simply the ipv4_address format, then the NETMASK or MASK operand cannot be used.

Note: The masklength must be between /1 and /30. The IP address must not be the subnet address or broadcast address for the network described by the IPv4 address/masklength pair (that is, it cannot be the first or last address in the subnet's range). For point-to-point links, a masklength of /30 is recommended.

ipv6_address/prefixlength

The primary IPv6 address of the interface, followed by the number of bits used to identify the prefix associated with the address.

Example: fe80:0:0:0:210:a4ff:fee3:956/64 indicates that a prefix of FFFF:FFFF:FFFF:FFFF:0:0:0:0 is to be used with an IP version 6 address of fe80:0:0:0:210:a4ff:fee3:956.

ADD ipv4_address/masklength

ADD ipv6_address/prefixlength

Adds an IPv4 address and subnet mask pair or IPv6 address and prefix pair to the home list of the interface.

CPU nn

Specifies the virtual processor to be used to run the device driver for the interface. nn must be an integer between 0 and 6.

CTC rdevno

Defines a real channel-to-channel interface.

DELete ipv4_address/masklength

DELete ipv6_address/prefixlength

Removes an IPv4 address and subnet mask pair or IPv6 address and prefix pair from the home list of the interface.

ETH rdevno routertype

Defines an LCS or QDIO Ethernet interface. ETH supports IPv4 and IPv6 router interface types. For IPv4, routertype can be PRImary, SECondary, or NONrouter. For IPv6, routertype can be IPV6PRImary, IPV6SECondary, or IPV6NONrouter. Only one IPv4 primary router interface (PRImary) can be defined for a QDIO device and only one IPv6 primary router interface (IPV6PRImary) can be defined for a QDIO device. While they can be the same interface, the QDIO devices do not have to be the same interface.

If the router type is specified for an LCS interface, the specification is ignored. OSA Support Facility (OSA/SF) is used to configure the router type for an OSA LCS interface. For more information about OSA/SF, see Open Systems Adapter-Express Customer's Guide and Reference.

HIPersockets rdevno

HS rdevno

Defines a real HiperSocket connection.

IP

ETHERNET

Indicates whether the transport for the link is ETHERNET or IP. An ETHERNET link operates at the Layer 2 level of the OSI model while an IP link operates at Layer 3. This operand can be specified only for real or virtual QDIO Ethernet devices.

Note: Router type is not supported for Layer 2.

IUCV userid

Defines an IUCV interface.

MASK mask

NETMASK mask

Defines or changes the subnet mask that is associated with the interface.

When defining an interface, the default value for the subnet mask is determined by the value of the first octet of the IP address:

If the value of the first octet is . . .	Then the default subnet mask is . . .
0-127	255.0.0.0
128-191	255.255.0.0
192-223	255.255.255.0

The default subnet mask applies only when defining an interface. Unless you use the mask option, changing the IP address of an existing interface leaves the mask unchanged.

Note: The mask must be between 128.0.0.0 and 255.255.255.252. The IP address must not be the subnet address or broadcast address for the network described by the IPv4 address/mask pair (that is, it cannot be the first or last address in the subnet's range). For point-to-point links, a subnet mask of 255.255.255.252 is recommended.

MTU mtusize

Defines or changes the Maximum Transmission Unit (MTU) size that is to be used on the interface. To determine the recommended MTU size, refer to the hardware documentation associated with the device.

If you specify 0 or omit this option, the TCP/IP stack selects an intelligent default. See Intelligent default MTU Values Based on the Device and Link Type.

NOFORWARD

NOFWD

Specifies that packets received on this link are not to be forwarded to another host (that is, packets destined for a foreign host are to be discarded) and that packets transmitted on this link must originate from the local host. Packets received for another host on this link are to be dropped, as are packets received for another host on any link and forwarded through this one. If you do not specify this option, packets received or transmitted on the link can be forwarded to another host.

PATHMTU

NOPATHMTU

Specifies the use of path MTU discovery on IPv4 routes for a given link. PATHMTU is the default when the PATHMTU operand is specified on the ASSORTEDPARMS statement in the TCP/IP configuration file. Otherwise, NOPATHMTU is the default. These operands have no effect on IPv6 routes. Path MTU discovery is always enabled for IPv6 and cannot be disabled.

POINTOPOINT ipv4_address

PTP ipv4_address

P2P ipv4_address

Defines or changes the IP address associated with the other end of a point-to-point interface.

PORTNAme portname

Specifies the Queued Direct I/O (QDIO) port name when it is being defined to be used by this interface. The portname is limited to a maximum of 8 characters and is optional. If you specify a port name, all TCP/IP stacks that share a QDIO device must specify the same port name. The port name is optional in all supported levels of the real or virtual OSA-Express® adapters.

PORTNUmber nn

Specifies the physical port or adapter number on the device when it is being defined to be used by this interface. This number depends on the device type:

For Channel-to-Channel (CTC) connections, specify 0 or 1.
For IBM Open Systems Adapter-Express operating in LCS mode, specify 0 or 1.
For IBM Open Systems Adapter-Express operating in QDIO mode, specify a decimal number in the range 0-15. The value of the port number depends on how many ports the OSA-Express adapter supports. If the port number is not specified, it will default to port 0.
Do not specify a port number for other devices.

UP

DOWN

Starts or stops the interface.

VCTC vdevno1 userid vdevno2

Defines a virtual channel-to-channel interface. A virtual CTC is defined and coupled to the specified user's virtual device.

VETH vdevno ownerid lanname

Defines a virtual QDIO Ethernet connection to the named guest LAN or virtual switch. If a VSWITCH name is specified, the ownerid must be SYSTEM. If no guest LAN or VSWITCH exists with the specified ownerid/lanname combination, a QDIO guest LAN will be created. The ownerid and lanname are limited to a maximum of 8 characters each.

VHIPersockets vdevno ownerid lanname

VHS vdevno ownerid lanname

Defines a virtual HiperSockets connection on the named guest LAN. If no guest LAN exists with the specified ownerid and lanname combination, a HiperSockets guest LAN will be created. The ownerid and lanname are limited to a maximum of 8 characters each.

VLAN ipv4vlan [ipv6vlan]

Specifies the identifier for a Virtual Local Area Network (VLAN). ipv4vlan and ipv6vlan are numbers from 1 to 4094. VLAN can be specified on QDIO Ethernet devices and HiperSockets devices.

For a QDIO Ethernet device, two VLANs may be specified. VLAN ipv4vlan specifies the IPv4 VLAN ID. You can optionally specify a separate VLAN ID for your IPv6 network by using ipv6vlan. If ipv6vlan is not specified, ipv4vlan is also used for the IPv6 network.

For a HiperSockets device, only one VLAN ID, ipv4vlan, may be specified.

Examples

To define an interface to a real HiperSocket adapter, enter the following:
```
ifconfig hsi0 10.1.0.1 mask 255.255.255.240 hs 3904 portname hs5a
```
Where:

hsi0 10.1.0.1

is the name and IP address of the HiperSocket interface

mask 255.255.255.240

is the subnet mask associated with the interface

hs 3904

is the real device address of the HiperSocket connection

portname hs5a

specifies the QDIO port name HS5A that is to be used by the interface

Note: A default Maximum Transmission Unit size of 4000 is used.
To define an interface to a virtual HiperSocket adapter that is connected to a z/VM guest LAN owned by SYSTEM and named PROD1, enter the following:
```
ifconfig vhsi0 10.2.0.1 vhs 3904 system prod1 mtu 8192
```
Where:

vhsi0 10.2.0.1

is the name and IP address of the virtual HiperSocket interface

vhs 3904 system prod1

defines the virtual HiperSocket connection at virtual device number 3904 on LAN name PROD1 of LAN owner SYSTEM.

mtu 8192

specifies that a Maximum Transmission Unit size of 8192 is to be used with this interface

Note: The default subnet mask (255.0.0.0) is used.
To define an IUCV interface to user TCPIP2, enter the following:
```
ifconfig iucv0 10.4.0.1/30 pointopoint 10.4.0.2 iucv tcpip2 mtu 9216
```
Where:

iucv0 10.4.0.1/30

is the name, IP address, and subnet mask of IUCV interface

pointopoint 10.4.0.2

defines the IP address at the other end of the interface

iucv tcpip2

defines the communication partner user ID as TCPIP2

mtu 9216

specifies that a Maximum Transmission Unit size of 9216 is to be used with this interface
To define an interface to a 1Gb Ethernet Open Systems Adapter Express at address 6904-6906 that will participate in a VLAN with an ID of 8, enter the following:
```
ifconfig eth0 192.60.25.6 eth 6904 primary mtu 1500 portname osa69 vlan 8
```
Where:

eth0 192.60.25.6

is the name and IP address of the Ethernet Open Systems Adapter Express interface

eth 6904 primary

specifies the QDIO interface with a real device number of 6904 and a router type of PRIMARY

mtu 1500

specifies that a Maximum Transmission Unit size of 1500 is to be used with this interface

portname osa69

specifies the QDIO port name OSA69 that is to be used by the interface

vlan 8

specifies the VLAN ID associated with the interface

Note: The default subnet mask (255.255.255.0) is used.
Now specify the IFCONFIG command with only the interface name, ETH0, to ensure the connection was properly defined:
```
ifconfig eth0
```
This displays the following:
```
ETH0     inet addr: 192.60.25.6 mask: 255.255.255.0                 
         UP MULTICAST MTU: 1500                                   
         vdev: 6904 rdev: 6904 type: QDIO ETHERNET portname: OSA69
         transport type: IP
         ipv4 router type: PRIMARY ipv6:DISABLED

         cpu: 0 forwarding: ENABLED ipv4 path MTU discovery: DISABLED
         RX bytes: 33932  TX bytes: 15534
```
To define an interface to an Ethernet Open Systems Adapter Express (OSA-Express2) at address 3000-3003 that will operate in layer 2 mode, enter the following:
```
ifconfig eth1 10.11.12.26 eth 3000 ethernet mtu 1500
```
Where:

eth1 10.11.12.26

is the name and IP address of the Ethernet Open Systems Adapter interface

eth 3000 ethernet

specifies the QDIO interface with a real device number of 3000 and a transport type of ethernet (layer 2)

mtu 1500

specifies that a Maximum Transmission Unit size of 1500 is to be used with this interface
Now specify the IFCONFIG command with only the interface name, ETH1, to ensure the connection was properly defined:
```
ifconfig eth1
```
This displays the following:
```
ETH1     inet addr: 10.11.12.26 mask: 255.0.0.0                    
         UP BROADCAST MULTICAST MTU: 1500                          
         vdev: 3000 rdev: 3000 type: QDIO ETHERNET portname: UNASSIGNED
         transport type: ETHERNET MAC address: 02-09-57-00-00-10        
         ipv6: DISABLED                                            
         cpu: 0 forwarding: ENABLED ipv4 path MTU discovery: DISABLED
         RX bytes: 110 TX bytes: 0                                 
```
To define an interface to IBM Ethernet Open Systems Adapter Express (OSA-Express2) running in LCS mode at address 3612-3613, enter the following:
```
ifconfig lcs0 10.59.12.5 mask 255.255.255.0 ethernet 3612 portnumber 1
```
Where:

lcs0 10.59.12.5

is the name and IP address of the Ethernet Open Systems Adapter Express interface

mask 255.255.255.0

is the subnet mask associated with the interface

ethernet 3612

specifies the LCS interface with a real device number of 3612

portnumber 1

specifies that port number 1 on the OSA adapter is to be used by this interface

Note: A default Maximum Transmission Unit size of 1500 is used.
Now specify the IFCONFIG command with only the interface name, LCS0, to ensure the connection was properly defined:
```
ifconfig lcs0
```
This displays the following:
```
 LCS0     inet addr: 10.59.12.5 mask: 255.255.255.0
          UP BROADCAST MULTICAST MTU: 1500
          vdev: 3612 rdev: 3612 type: LCS ETHERNET portnumber: 1
          cpu: 0 forwarding: ENABLED ipv4 path MTU discovery: DISABLED
          RX bytes: 13965 TX bytes: 38904
```

To display information about an interface that is not up, enter the following:

ifconfig lcs1

May appear as follows:

 LCS1     inet addr: 10.200.13.78 mask: ?
          DOWN BROADCAST MULTICAST MTU: ?
          vdev: 1F08 rdev: 1F08 type: LCS ETHERNET portnumber: 0
          cpu: 0 forwarding: ENABLED ipv4 path MTU discovery: DISABLED
          RX bytes: 0 TX bytes: 0

Note: Question marks (?) are displayed for the subnet mask and Maximum Transmission Unit size because they are not known.

To display the TCP/IP configuration file statements necessary to define a channel-to-channel (CTC) interface, enter the following:
```
ifconfig ctc0 10.14.6.1/30 vctc 800 tcpip2 3600 ptp 10.14.6.2 portnumber 0 -show
```
Where:

ctc0 10.14.6.1/30

is the name, IP address, and subnet mask of the CTC interface

vctc 800 tcpip2 3600

is the virtual CTC at virtual device number 800 that is coupled to virtual device number 3600 owned by user TCPIP2

ptp 10.14.6.2

is the IP address at the other end of the interface

-show

displays the TCP/IP server configuration file changes

Note: Because an MTU was not specified on the command, the LINK MTU is configured as 0, forcing the stack to choose an intelligent default according to Intelligent default MTU Values Based on the Device and Link Type.
The following is displayed:
```
; Generated by <IFCONFIG ctc0 10.14.6.1/30 vctc 800 tcpip2 3600 ptp 10.14.6.2
; portnumber 0 -show>
; 25 Mar 2005 12:16:57 
DEVICE DEV@800  CTC 800 
LINK CTC0 CTC 0 DEV@800  MTU 0 
HOME 
10.14.6.1 255.255.255.252 CTC0
START DEV@800
```
To display the TCP/IP configuration file statements necessary to define a virtual HiperSocket interface to another virtual HiperSocket connection, enter the following:
```
ifconfig vhs3 10.2.0.1 mask 255.255.0.0 vhs 3500 tcpip41 subnt96 -show
```
Where:

vhs3 10.2.0.1

is the name and IP address of the virtual HiperSocket interface.

mask 255.255.0.0

is the subnet mask associated with the interface.

vhs 3500 tcpip41 subnt96

defines the virtual HiperSocket connection at virtual device number 3500 on LAN name SUBNT96 owned by user TCPIP41.

-show

displays the TCP/IP server configuration file changes.

Note: Because an MTU was not specified on the command, the LINK MTU is configured as 0, forcing the stack to choose an intelligent default according to Intelligent default MTU Values Based on the Device and Link Type.
The following is displayed:
```
; Generated by <IFCONFIG vhs3 10.2.0.1 mask 255.255.0.0 vhs 3500 tcpip41 subnt96
; -show> 
; 25 Mar 2005 12:20:54 
DEVICE DEV@3500  HIPERS 3500 
LINK VHS3 QDIOIP DEV@3500  MTU 0 
HOME 
10.2.0.1 255.255.0.0 VHS3 
START DEV@3500
```
To connect a virtual QDIO device to an existing QDIO guest LAN named TEST1 that is owned by user TCPIP41, display any CP or NETSTAT commands that were used to change the system, and apply these changes to a specific TCP/IP stack virtual machine named TCPIP39, enter the following:
```
ifconfig eth0 10.1.1.1 veth 3400 tcpip41 test1 -v -tcp tcpip39
```
Where:

eth0 10.1.1.1

is the name and IP address of the virtual QDIO Ethernet interface

veth 3400 tcpip41 test1

is the existing QDIO connection at virtual device number 3400 named TEST1 that is owned by user TCPIP41

-v

specifies the -Verbose command option, which displays any CP or NETSTAT commands that were used to change the running system

-tcp tcpip39

applies these changes to a z/VM TCP/IP stack virtual machine named TCPIP39
The following is displayed:
```
* NETSTAT TCP TCPIP39 CP QUERY LAN TEST1 OWNER TCPIP41
* NETSTAT TCP TCPIP39 CP DEFINE NIC 3400 QDIO         
* NETSTAT TCP TCPIP39 CP COUPLE 3400 TCPIP41 SUBNT176 
* OBEYFILE IFCONFIG CMSUT1 A ( TCP TCPIP39            
```
To define a real HiperSocket connection, display any CP or NETSTAT commands that were used to change the system, and apply these changes to a specific TCP/IP stack virtual machine named TCPIP2, enter the following:
```
ifconfig hs0 10.1.2.1 hs fb00 -v -tcp tcpip2
```
Where:

hs0 10.1.2.1

is the name and IP address of the HiperSocket interface

hs fb00

is the real device address of the HiperSocket connection

-v

specifies the -Verbose command option, which displays any CP or NETSTAT commands that were used to change the running system

-tcp tcpip2

applies these changes to a z/VM TCP/IP stack virtual machine named TCPIP2
The following is displayed:
```
* NETSTAT TCP TCPIP2 CP ATTACH FB00 TCPIP2 FB00
* NETSTAT TCP TCPIP2 CP ATTACH FB01 TCPIP2 FB01
* NETSTAT TCP TCPIP2 CP ATTACH FB02 TCPIP2 FB02
* OBEYFILE IFCONFIG CMSUT1 A ( TCP TCPIP2      
```
To define a virtual CTC connection and display any CP or NETSTAT commands that were used to change the system, enter the following:
```
ifconfig ctc0 10.1.3.1/30 vctc 800 tcpip2 3600 ptp 10.1.3.2 portnum 1 -v
```
Where:

ctc0 10.1.3.1/30

is the name, IP address, and subnet mask of the CTC interface

vctc 800 tcpip2 3600

is the virtual CTC at virtual device number 800 that is coupled to TCPIP2 user's virtual device number 3600

ptp 10.1.3.2

defines the IP address at the other end of the interface

portnum 1

specifies the adapter number of the CTC device

-v

specifies the -Verbose command option, which displays any CP or NETSTAT commands that were used to change the running system
The following is displayed:
```
* NETSTAT TCP TCPIP CP DEFINE 3088 800       
* NETSTAT TCP TCPIP CP DEFINE 3088 801       
* NETSTAT TCP TCPIP CP COUPLE 800 TCPIP2 3600
* NETSTAT TCP TCPIP CP COUPLE 801 TCPIP2 3601
* OBEYFILE IFCONFIG CMSUT1 A ( TCP TCPIP     
```
To define an interface to a real Open Systems Adapter Express at address 5200-5202 using IP version 6, enter the following:
```
ifconfig eth0 1080:0:0:0:210:a4ff:fee3:956/64 eth 5200 secondary ipv6primary 
   portname osa52
```
```
ifconfig eth0 1080:0:0:0:210:a4ff:fee3:956/64 eth 5200 secondary  
   ipv6primary portname osa52
```
Where:

eth0 1080:0:0:0:210:a4ff:fee3:956/64

is the name, IPv6 address and prefix length of the Ethernet Open Systems Adapter Express interface

eth 5200 secondary ipv6primary

specifies the QDIO interface with a real device number of 5200 as a secondary IPv4 router and a primary IPv6 router

portname osa52

specifies the QDIO port name OSA52 that is to be used by the interface

Note: A default Maximum Transmission Unit size of 1500 is used.
To add the IPv4 address 192.168.0.9 with a subnet mask of 255.255.255.0 to interface eth1 (which must already be defined), enter the following:
```
ifconfig eth1 add 192.168.0.9/24
```
Where:

eth1

is the interface name

add 192.168.0.9/24

is the IPv4 address to be added to the interface followed by the number of high order bits specified by the subnet mask for the interface
To delete the IPv6 address 1080:0:0:0:AB32:800:FF83:10 with prefix length of 64 from interface eth3, enter the following:
```
ifconfig eth3 delete 1080:0:0:0:AB32:800:FF83:10/64
```
Where:

eth3

is the interface name

delete 1080:0:0:0:AB32:800:FF83:10/64

is the IPv6 address to be deleted from the interface followed by the prefix length associated with that address

In the following example eth0 and eth1 are both attached to the 9.60.59.0/26 subnet. The display below shows the IFCONFIG output after eth1 has suffered an outage:

ifconfig -all                                               
ETH0     inet addr: 9.60.59.6 mask: 255.255.255.192         
         UP BROADCAST MULTICAST MTU: 1500                   
         vdev: 0600 type: QDIO ETHERNET portname: UNASSIGNED
         transport type: IP
         ipv4 router type: NONROUTER ipv6: DISABLED         
         LAN owner: SYSTEM name: SUBNTA                     
         cpu: 0 forwarding: ENABLED ipv4 path MTU discovery: DISABLED
         RX bytes: 0 TX bytes: 0                            
                                                            
ETH1     inet addr: 9.60.59.7 mask: 255.255.255.192         
         DOWN MTU: 1500                                     
         vdev: 0700 type: QDIO ETHERNET portname: UNASSIGNED
         transport type: IP
         ipv4 router type: NONROUTER ipv6: DISABLED         
         LAN owner: SYSTEM name: SUBNTA                     
         cpu: 0 forwarding: ENABLED ipv4 path MTU discovery: DISABLED
         RX bytes: 0 TX bytes: 0                            
         IPv4 Takeover Link: ETH0

The IPv4 Takeover Link field in the eth1 output shows that IPv4 ARP responsibility for eth1's IP addresses has been taken over by eth0. For more information on interface takeover, see Interface Takeover for Local Area Networks.

Usage Notes

Entering the IFCONFIG command with no other parameters specified displays all active interfaces.
Use the IFCONFIG command to configure the following types of interfaces:
- LCS
- QDIO
- HiperSocket
- IUCV
- CTC
Once an interface is defined using IFCONFIG, the only operands that may be changed are the IP address, subnet mask, peer IP address and MTU size. The interface may also be started and stopped. A particular real device can be defined only once to TCP/IP.
There are certain LCS devices that have multiple network adapters, such as the IBM Open Systems Adapter. IFCONFIG does not permit a second interface to be defined that references a device number already in use by TCP/IP. Therefore, an additional device must be defined for each additional network adapter that you wish to use.
While IFCONFIG attempts to ensure that the chosen device number and interface type are compatible, there are circumstances where LCS and CTC devices are indistinguishable until TCP/IP actually starts using the device. In these cases the file StackID TCPERROR, which contains details of the error, is sent to the issuer of the IFCONFIG command. Depending on the exact nature of the error, it may be necessary to recycle the z/VM TCP/IP stack in order to delete the erroneous device from the TCP/IP configuration.
In order to use IFCONFIG to create a device that is enabled for IPv6, you must specify an IPv6 address either as the primary address or on the ADD operand of the initial command that is used to create the device. Otherwise, even though the device itself is IPv6 capable, it is not enabled in the TCP/IP stack and cannot be enabled later without recycling the stack.
VLAN configuration information can be found in Planning for Guest LANs and Virtual Switches in z/VM: Connectivity.
Be aware that the IFCONFIG command makes use of the NETSTAT and OBEYFILE commands to facilitate its operations. To use this command to make network interface changes, your user ID must be included in the OBEY list in the TCP/IP server configuration file.
Note also that one or more considerations regarding use of the NETSTAT and OBEYFILE commands might apply when you use the IFCONFIG command. For specific information, see the Usage Notes for these commands.
When running MPRoute, various defaults are taken when dealing with interfaces not defined in the MPRoute configuration file. This may cause undesirable routing scenarios when using IFCONFIG to configure new interfaces to the stack. In order to avoid this, ensure you have
```
GLOBAL_OPTIONS
IGNORE_UNDEFINED_INTERFACE=YES;
```
specified in the MPRoute configuration file if you plan on using IFCONFIG in this manner.
The amount of information returned on an IFCONFIG query may differ depending on whether or not the user issuing the command is in the OBEY list of the TCP/IP server.

Return Codes

Return Code: Description
0: The command completed successfully.
4: The command completed successfully, but a warning condition was detected.
8: The command was not specified correctly.
12: An error was encountered.
16: An unexpected condition was encountered.