Change TCP/IP Interface (CHGTCPIFC)

The Change TCP/IP Interface (CHGTCPIFC) command is used to change an existing interface in the Transmission Control Protocol/Internet Protocol (TCP/IP) configuration. The interfaces defined by the CHGTCPIFC command are logical interfaces. They are not physical interfaces. Each interface is associated with a line description. The line description is the physical connection from the system to the TCP/IP network.

The i5/OS TCP/IP implementation supports multihoming. This allows you to specify either a single interface or multiple interfaces per line description. You can have your system appear as any one or combination of the following:

A single host on a network over a communications line
Multiple hosts on the same network over the same communications line
Multiple hosts on different networks over the same communications line
Multiple hosts on the same network over multiple communications lines
Multiple hosts on different networks over multiple communications lines

Notes:

If you attempt to change a value for an interface that will invalidate a route or remote system information (RSI) associated with the interface, the change will not be allowed.
In SNMP, an interface is a physical interface. The physical interface relates directly to an input/output processor (IOP).
The interface table is shipped with a default interface of 127.0.0.1. The line description value associated with the 127.0.0.1 interface is *LOOPBACK. The host table is also shipped with an entry that has an internet address of 127.0.0.1 and host names of LOOPBACK and LOCALHOST.

Attention: Before attempting to start an X.25 interface, ensure that the remote system information (RSI) for non-DDN X.25 interfaces that use a permanent virtual circuit (PVC) is configured. Use the Add TCP/IP Remote System Information (ADDTCPRSI) command to do this. Incoming data from a remote system on the X.25 network is not processed unless an RSI entry for the PVC is configured on the X.25 interface before the interface is started.

Restrictions:

You must have input/output system configuration (*IOSYSCFG) special authority to run this command.
Only certain values can be changed using this command. The values that can be changed depend on the status of the interface, the status of the dependent routes, and the remote system information configured.

Parameters

Keyword	Description	Choices	Notes
INTNETADR	Internet address	Character value	Optional, Positional 1
ALIASNAME	Alias name	Simple name, SAME, NONE	Optional
LIND	Line description	Name, SAME, VIRTUALIP, LOOPBACK, OPC	Optional, Positional 2
SUBNETMASK	Subnet mask	Character value, SAME, HOST	Optional, Positional 3
LCLIFC	Associated local interface	Character value, SAME, NONE	Optional
TOS	Type of service	SAME, MINDELAY, MAXTHRPUT, MAXRLB, MINCOST, NORMAL	Optional
MTU	Maximum transmission unit	576-16388, SAME, LIND	Optional
AUTOSTART	Autostart	SAME, YES, *NO	Optional
PVCLGLCHLI	PVC logical channel identifier	Values (up to 64 repetitions): Character value, SAME, NONE	Optional
IDLVCTTIMO	X.25 idle circuit timeout	1-600, *SAME	Optional
MAXSVC	X.25 maximum virtual circuits	0-64, *SAME	Optional
DDN	X.25 DDN interface	SAME, YES, *NO	Optional
BITSEQ	TRLAN bit sequencing	SAME, MSB, *LSB	Optional

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Internet address (INTNETADR)

Specifies the internet address. The internet address is specified in the form nnn.nnn.nnn.nnn, where nnn is a decimal number ranging from 0 through 255. An internet address is not valid if it has a value of all binary ones or all binary zeros for the network identifier (ID) portion or the host ID portion of the address. If the internet address is entered from a command line, the address must be enclosed in apostrophes.

Note: If an internet address is not provided with the command, the alias name must be provided and it will be used as the key value for the command.

Alias name (ALIASNAME)

Specifies a name that can be used in place of the internet address. The name must be unique among all of the interfaces on the system.

Note: If an internet address is not provided with the command, the alias name will be the key for the command. If an internet address is provided, the alias name can be changed from its current value.

*SAME: The current alias name is used.
*NONE: No alias name is associated with the TCP/IP interface you are currently defining.
simple-name: Specify a name for the interface. The alias name must be 25 characters or less.

Line description (LIND)

Specifies the name of the line description associated with the to be changed interface. The following conditions are based on the interface type that the user defines:

Token-ring: The name must be previously defined on the Create Line Description (Token-Ring Network) (CRTLINTRN) command.
X.25: The name must be previously defined on the Create Line Description (X.25) (CRTLINX25) command.
Ethernet: The name must be previously defined on the Create Line Description (Ethernet) (CRTLINETH) command.
DDI: The name must be previously defined on the Create Line Description (DDI Network) (CRTLINDDI) command.
Frame relay: The name must be previously defined on the Create Line Description (Frame Relay Network) (CRTLINFR) command.
Wireless: The name must be previously defined on the Create Line Description (Wireless Network) (CRTLINWLS) command.
Twinax (TDLC): The name must be previously defined on the Create Line Description (TDLC) (CRTLINTDLC) command.

TCP/IP can also be used on certain line descriptions attached to these network interfaces (NWI):

A frame relay NWI using a frame relay, token ring, Ethernet, or DDI line description.
- The frame relay NWI is created using the Create Network Interface Frame Relay Network (CRTNWIFR) command.
- The line description is created using the appropriate Create Line command and attached to the frame relay NWI by specifying the NWI and NWIDLCI parameters.

*SAME

The same line description existing for this interface is used.

*VIRTUALIP

The virtual interface is a circuitless interface. It is used in conjunction with the associated local interface (LCLIFC) when adding standard interfaces. This special value is used to accommodate any of the following cases:

Load balancing. This is the means of having a fixed source IP address regardless of which interface the traffic is being distributed.
Frame-relay multi-access network to define the local network IP address. This allows for multiple virtual circuits to share the same IP network.
Alternate method of network access translation (NAT). This eliminates the need for a NAT box by assigning a globally unique single IP address directly to the box without the need to define an entire network.
Unnumbered networks. This provides a means of associating a local source IP address for an unnumbered point-to-point network.

*OPC

This special value is used if you are adding an OptiConnect interface over TCP/IP. This interface is attached to the optical bus (OptiConnect).

*LOOPBACK

The interface being changed by this command is the loopback or LOCALHOST interface. Because processing associated with loopback does not extend to a physical line, there is no line description associated with a loopback address. This special value must be used for any internet address that has a first octet value of 127.

name

Specify the name of the line description to be used for this interface.

Subnet mask (SUBNETMASK)

Specifies the subnet mask, which is a bit mask that defines the part of the network where this interface attaches. The mask is a 32-bit combination that is logically ANDed with the internet address to determine a particular subnetwork. The bits of the mask set to the value one (1) determine the network and subnetwork portions of the address. The bits set to the value zero (0) determine the host portion of the address.

The bits that identify the subnetwork are not required to be adjacent in the address. However, if this subnet mask value is changed, it might invalidate or affect the routes using this interface. To prevent this, keep the subnet bits contiguous and located in the most significant bits of the host address.

Note: The network portion must be equal to one bits in the subnetmask. The host portion of an address must be at least two bits wide.

*SAME: The same subnetmask existing for this interface is used.
*HOST: The subnet mask value used will be 255.255.255.255. Specify this value for use with Proxy ARP (Address Resolution Protocol).
character-value: Specify the subnet mask for the network field and host address field of the internet address that defines a subnetwork. The subnet mask is in the form nnn.nnn.nnn.nnn, where nnn is a decimal number ranging from 0 through 255. The subnet mask must mask off all bits of the network class's network ID portion of the internet address. For more detailed information on subnet masks and an example, see the help for the Add TCP/IP Interface (ADDTCPIFC) command.

Associated local interface (LCLIFC)

Use this parameter to associate the interface you are currently defining with an existing local TCP/IP interface.

The associated local interface (LCLIFC) is used to allow 'transparent subnetting' (also known as 'Proxy Arp') between the associated interfaces, to define Frame Relay unnumbered networks or for load balancing.

Condition for using the LCLIFC for unnumbered networks:

The line type of the interface you are changing MUST be Frame Relay.

Conditions for using LCLIFC for transparent subnetting:

The network of the associated local interface must be broadcast capable.
The interface you are changing must be defined as a subnet of the network you are associating it with (using LCLIFC).

Condition for using the LCLIFC for load balancing:

This is the means of having a fixed source IP address regardless of which interface the traffic is being distributed.
The line type of the associated local interface must be *VIRTUALIP.

Note: You can only use LCLIFC to associate this interface to another interface that is already defined. Once associated, the interface defined in LCLIFC must always be started prior to starting this interface.

*SAME: The current associated local interface is used.
*NONE: No TCP/IP interface is associated with the interface you are currently defining.
character-value: Specify the internet address of the interface you want to associate with the interface you are currently defining.

Type of service (TOS)

Specifies the type of service to be used. The type of service defines how the internet hosts and routers should make trade-offs between throughput, delay, reliability, and cost.

*SAME

The type of service does not change.

*NORMAL: Normal service is used for delivery of data.

*MINDELAY: Minimize delay means that prompt delivery is important for data on this connection.

*MAXTHRPUT: Maximize throughput means that a high data rate is important for data on this connection.

*MAXRLB: Maximize reliability means that a higher level of effort to ensure

*MINCOST: Minimize monetary cost means that lower cost is important for data on this connection.

Maximum transmission unit (MTU)

Specifies the maximum size (in bytes) of IP datagrams that can be transmitted through this interface. A datagram is a basic unit of information passed over an internet network. The minimum size of any maximum transmission unit value is 576 bytes. If this value is changed it affects the MTUs of routes using this interface.

*SAME

The existing maximum transmission unit value for this interface is used.

*LIND

The MTU is determined by the information specified in the line description. If *LIND is specified, the MTU is equal to the largest amount of data that can be transmitted on the line.

maximum-transmission-unit

Specify a value for the maximum transmission unit in bytes. The maximum MTU that can be specified for this interface depends on the type of physical connection to the network. The following table lists the maximum MTU values that can be specified based on the line type:

X.25: 4096
Token ring (4 meg): 4060
Token ring (16 meg): 16388
Ethernet 802.3: 1492
Ethernet Version 2: 1500
DDI: 4352
Frame relay: 8177
Wireless 802.3: 1492
Wireless Version 2: 1500
Twinax (TDLC): 4105

Notes:

It is suggested that the same MTU values be used for all interfaces on the same network.
The actual MTU value used for an interface is resolved during interface activation. This value is the minimum of either the specified MTU value for the interface or the largest amount of data that can be transmitted on the line.
The same MTU value does not need to be specified for all interfaces defined on the same subnet. However, all interfaces must have an MTU that does not exceed the value used when *LIND is specified for the interface MTU.
To view the MTU value actually used for an interface, do the following:
1. Use the ADDTCPIFC command to add the interface.
2. Use the Start TCP/IP Interface (STRTCPIFC) command to activate the interface.
3. Use the Work with TCP/IP Status (WRKTCPSTS or NETSTAT) command to view the actual MTU value of the interface in bytes.

PVC logical channel identifier (PVCLGLCHLI)

Specifies the permanent virtual circuit (PVC) logical channel identifiers that can be established on an X.25 interface by the TCP/IP protocol stack. Up to 64 unique channel identifiers may be specified. These logical channel identifiers must exist in the X.25 line description.

With this parameter you can share the line with other communications software, such as Systems Network Architecture (SNA). It prevents the TCP/IP protocol stack from monopolizing the PVCs defined for the line.

Notes:

This parameter is valid only for an interface defined on an X.25 line description.
PVCs cannot be used in a DDN network.
When specifying PVCs for an X.25 interface, all interfaces on the same X.25 network must have this same set of PVC logical channel identifiers specified. This is especially important if one or more remote system information (RSI) entries will use a PVC to connect to the RSI entry's remote system on the X.25 network.
If the RSI entries are defined such that two or more remote internet addresses can be reached across the same PVC, that PVC is shared.
The sum of the maximum switched virtual circuits (MAXSVC) and the number of PVCs cannot exceed 64.

*SAME: The existing PVC logical channel identifier values for this interface are used.
*NONE: All existing PVC logical channel identifier values for this interface are removed. If no PVC values are defined, *NONE is shown.
001-FFF: Specify the PVC logical channel identifier value. Up to 64 PVC logical channel identifiers can be specified.

X.25 idle circuit timeout (IDLVCTTIMO)

Specifies the duration (in seconds) that the TCP/IP Network Access Manager (NAM) waits before clearing an idle virtual circuit established on an X.25 link. Clearing an idle virtual circuit frees resources on the network. TCP/IP automatically reestablishes virtual circuits when required to send or receive data. Virtual circuits are transparent to a TCP/IP client and have no noticeable effect on TCP connections.

Note: This parameter is valid only for switched virtual circuits (SVCs) on an interface defined on an X.25 line description. It is not valid for permanent virtual circuits (PVCs).

*SAME: The existing idle virtual circuit timeout value for this interface is used.
1-600: Specify the number of seconds to be used for the idle virtual circuit timeout.

X.25 maximum virtual circuits (MAXSVC)

Specifies the maximum number of concurrent switched virtual circuits (SVC) that can be established on an X.25 interface by the TCP/IP protocol stack.

Note: The sum of the maximum switched virtual circuits (MAXSVC) and the number of PVCs cannot exceed 64.

*SAME: The existing maximum SVC value for this interface is used.
0-64: Specify the number of SVCs that the TCP/IP protocol stack can use simultaneously. If 64 is specified, the number of SVCs that are configured is calculated by adding the number of *SVCIN, *SVCOUT and *SVCBOTH SVCs defined for the line description (LIND) being used by this interface. This is the maximum number of SVCs that can be authorized for processing by the TCP/IP protocol stack.

X.25 DDN interface (DDN)

Specifies whether the X.25 interface is connected to the Defense Data Network. The DDN network is a special type of X.25 network used by TCP/IP customers with special security needs.

Note: This parameter is valid only for switched virtual circuits (SVCs) on an interface defined on an X.25 line description. It is not valid for permanent virtual circuits (PVCs).

Warning:

If you specify multiple interfaces to the same X.25 network, the DDN value should be equal for all of those interfaces. This is not enforced by the ADDTCPIFC or CHGTCPIFC commands.

If the X.25 network is the DDN network, do not define the remote system information for any of the remote systems on the network. The remote system information for the DDN X.25 network is determined from the destination IP address.

*SAME: The existing DDN value for this interface is used.
*NO: The X.25 interface is not connected to the Defense Data Network.
*YES: The X.25 interface is connected to the Defense Data Network.

TRLAN bit sequencing (BITSEQ)

Specifies the order, most or least significant bit first, in which the Address Resolution Protocol (ARP) places the bits in the hardware address. This parameter is valid only for a token-ring local area network (TRLAN) line.

Note: All interfaces defined to a single token-ring line must have the same BITSEQ value. This is checked by the CHGTCPIFC code to ensure consistent values.

*SAME: The existing bit sequence value for this interface is used.
*MSB: The most significant bit is placed first.
*LSB: The least significant bit is placed first.

Examples

Example 1: Changing Autostart Value

CHGTCPIFC   INTNETADR('130.14.3.5')  AUTOSTART(*NO)

Assuming that an interface identified by 130.14.3.5 exists, this command changes the autostart value from *YES to *NO. The interface is not automatically started when the STRTCP command is entered.

Example 2: Changing MAXSVC and IDLVCTTIMO

CHGTCPIFC   INTNETADR('8.77.0.21')  INDLVCTTIMO(45)  MAXSVC(15)

This command changes the idle virtual circuit time-out to 45 seconds and the maximum number of concurrent SVCs allowed to be used by TCP/IP on this interface to 15.

Example 3: Change an Interface for a Twinax Line that is Using an Associated Local Interface

CHGTCPIFC   INTNETADR('199.1.1.99')  LCLIFC('199.1.1.1')

This command will change the TCP/IP interface for the twinax line named TDLCLINE. This interface will be associated with local interface 199.1.1.1. This means that the devices attached to twinax line 199.1.1.99 can take advantage of 'appearing' to be on the same network as the local 199.1.1.1 interface (transparent subnetting). No special routing is required to ensure packets from the twinax connnected hosts can travel to the local 199.1.1.0 network. Also, hosts on the 199.1.1.0 network can also reach the twinax hosts without any additional routing on the host systems.

Example 4: Changing ALIASNAME

CHGTCPIFC   INTNETADR('132.15.7.32')  ALIASNAME(TEST_NETWORK)

This command changes the alias name for this interface to TEST_NETWORK.

Example 5: Changing the interface using the ALIASNAME

CHGTCPIFC   ALIASNAME(TEST_NETWORK)  AUTOSTART(*YES)

This command changes the auto start value for the interface named TEST_NETWORK.