Change TCP/IP Attributes (CHGTCPA)

The Change TCP/IP Attributes (CHGTCPA) command is used to change the TCP, UDP, IP, and ARP protocol layer attributes. The changes take effect immediately.

The protocols (IPv4, IPv6, or both) affected by the following keywords and the default values for the keywords follow. These values are also used if *DFT is specified for the keyword.

Keyword

Affected Protocols and Default Value

TCPKEEPALV

IPv4 and IPv6; 120 minutes

TCPURGPTR

IPv4 and IPv6; *BSD

TCPRCVBUF

IPv4 and IPv6; 65535 bytes

TCPSNDBUF

IPv4 and IPv6; 65535 bytes

TCPR1CNT

IPv4 and IPv6; 3

TCPR2CNT

IPv4 and IPv6; 16

TCPMINRTM

IPv4 and IPv6; 250 milliseconds

TCPCLOTIMO

IPv4 and IPv6; 120 seconds

TCPCNNMSG

IPv4 and IPv6; *THRESHOLD

UDPCKS

IPv4 only; *YES

IPPATHMTU

IPv4 and IPv6; *YES, 10 minutes

IPDTGFWD

IPv4 and IPv6; *NO

IPSRCRTG

IPv4 only; *YES

IPRSBTIMO

IPv4 only; 10 seconds

IPTTL

IPv4 only; 64

IPQOSENB

IPv4 only; *NO

IPDEADGATE

IPv4 and IPv6; *YES, 2 minutes

ARPTIMO

IPv4 only; 15 minutes

ECN

IPv4 only; *NO

NFC

IPv4 only; *YES, 300 seconds, 10MB

LOGPCLERR

IPv4 only; *NO

DHCPUNQID

IPv4 and IPv6; If the system has not generated a DHCP unique identifier, by default one will be generated the first time it is needed.

IP6ERRLMT

IPv6 only; 10

IP6ERRRATE

IPv6 only; 10 messages per second

IP6HOPLMT

IPv6 only; 64

IP6DUPRTLS

IPv6 only; *RTR

IP6TMPAVL

IPv6 only; 7 days

IP6TMPAPL

IPv6 only; 1 day

IP6TMPAXP

IPv6 only; *DFT

Restriction:

• You must have input/output system configuration (*IOSYSCFG) special authority to run this command.

Parameters

TCP keep alive (TCPKEEPALV)

Specifies the amount of time, in minutes, that TCP waits before sending out a probe to the other side of a connection. The probe is sent when the connection is otherwise idle, even when there is no data to be sent.

The transmission of keep-alive packets is controlled by individual sockets applications through use of the SO_KEEPALIVE socket option. For more information see the Socket programming topic collection in the IBM i Information Center at http://www.ibm.com/systems/i/infocenter/.

*SAME

The value does not change.

*DFT

The keep-alive time interval value of 120 minutes is used.

1-40320

Specify a keep-alive time interval in minutes. Valid values range from 1 through 40320 minutes (28 days).

TCP urgent pointer (TCPURGPTR)

Specifies which convention to follow when interpreting which byte the urgent pointer in the TCP header points to. The urgent pointer in the TCP header points to either the byte immediately following the last byte of urgent data (BSD convention) or the last byte of the urgent data (RFC convention).

Note: This value must be consistent between the local and remote ends of a TCP connection. Socket applications that use this value must use it consistently between the client and server applications. This value is set on a system basis. All applications using this system will use this value.

*SAME

The value does not change.

*BSD

Use the BSD defined convention. The TCP urgent pointer points to the byte immediately following the last byte of urgent data. This is the initial value.

*RFC

Use the RFC defined convention. The TCP urgent pointer points to the last byte of the urgent data.

TCP receive buffer size (TCPRCVBUF)

Specifies what to allocate for the default receive buffer size. The TCP receive window size is based on this value. Decreasing this value decreases the amount of data that the remote system can send before being read by the local application.

Notes:

1. The default User Datagram Protocol (UDP) receive buffer size is 65535. If the TCP receive buffer size is specified as greater than 65535 then the UPD receive buffer size will be changed to equal the TCP receive buffer size. If the TCP receive buffer size is specified as less than 65535 then the default UDP buffer size will be used.
2. This value is also used as the default receive buffer size by IP over SNA processing.
3. This value is the default TCP receive buffer size. An individual application can override this value by using the SO_RCVBUF socket option. For more information see the Socket programming topic collection in the IBM i Information Center at http://www.ibm.com/systems/i/infocenter/.

*SAME

The value does not change.

*DFT

The default TCP receive buffer size of 65535 (64K - 1) is used.

512-8388608

Specify the number of bytes to be used for the TCP receive buffer size.

TCP send buffer size (TCPSNDBUF)

Specifies the TCP send buffer size. This parameter informs TCP what to use for the default send buffer size. The TCP send buffer size provides a limit on the number of outgoing bytes that are buffered by TCP. Once this limit is reached, attempts to send additional bytes may result in the application blocking until the number of outgoing bytes buffered drops below this limit. The number of outgoing bytes buffered is decremented when the remote system acknowledges the data sent.

Notes:

1. This value is used also as the default send buffer size by IP over SNA processing.
2. The default UDP send buffer size is 65535..
3. This value is the default TCP send buffer size. An individual application can override this value by using the SO_SNDBUF socket option. For more information see the Socket programming topic collection in the IBM i Information Center at http://www.ibm.com/systems/i/infocenter/.

*SAME

The value does not change.

*DFT

The default TCP send buffer size of 65535 (64K - 1) is used.

512-8388608

Specify the number of bytes to be used for the TCP send buffer size.

TCP R1 retransmission count (TCPR1CNT)

Specifies the TCP R1 retransmission count value. This parameter is a counter that specifies the number of TCP retransmissions that will be attempted before TCP requests a different network route from IP.

Note: The R1 retransmission count value must be less than the R2 retransmission count value.

*SAME

The value does not change.

*DFT

The default TCP R1 retransmission count value of 3 is used.

1-15

Specify the TCP R1 retransmission count value.

TCP R2 retransmission count (TCPR2CNT)

Specifies the TCP R2 retransmission count value. This parameter is a counter that specifies the number of TCP retransmissions that will be attempted before TCP assumes that the connection has been lost and stops retransmitting.

Note: The R2 retransmission count value must be greater than the R1 retransmission count value.

*SAME

The value does not change.

*DFT

The default TCP R2 retransmission count value of 16 is used.

2-16

Specify the TCP R2 retransmission count value.

TCP minimum retransmit time (TCPMINRTM)

Specifies the TCP minimum retransmit time value which is the lowest amount of time (expressed in milliseconds) to elapse before TCP decides that a transmitted packet is lost and needs to be sent again. After each unsuccessful attempt to transmit a packet, this value will be doubled until it reaches a maximum value of 2 minutes.

*SAME

The value does not change.

*DFT

The default TCP minimum retransmit time value of 250 milliseconds is used.

100-1000

Specify the number of milliseconds to be used for the TCP minimum retransmit time value.

TCP time-wait timeout (TCPCLOTIMO)

This parameter indicates the amount of time, in seconds, for which a socket pair (client IP address and port, server IP address and port) cannot be reused after a connection is closed.

Note: Setting the TCP time wait timeout value to 0 means that a timer will not be used.

*SAME

The value does not change.

*DFT

The default TCP time wait timeout value of 120 seconds is used.

0-14400

Specify the number of seconds to be used for the TCP time wait timeout value.

TCP close connection message (TCPCNNMSG)

Specifies whether abnormally closed TCP connections will be logged via messages to the QTCP message queue. TCP connections could be abnormally closed for the following reasons:

• TCP connection closed due to the 10 minute Close_Wait_timeout.
• TCP connection closed due to the R2 retry threshold being exceeded.
• TCP connection closed due to the keepalive time-out value being exceeded.

*SAME

The value does not change.

*THRESHOLD

At most, one abnormally closed TCP connection message per minute will be logged. TCPCNNMSG(*THRESHOLD) is the initial value.

*ALL

All abnormally closed TCP connections will be logged. Note that there are some conditions that could cause MANY closed connection messages to be logged at the same time.

*NONE

Abnormally closed TCP connections will not be logged.

UDP checksum (UDPCKS)

Specifies whether UDP processing should generate and validate checksums. It is strongly recommended that you specify UDPCKS(*YES) to use UDP checksum processing. If you are concerned about obtaining the best possible performance and are not concerned with the protection provided by UDP checksum processing, specify UDPCKS(*NO).

*SAME

The value does not change.

*YES

Checksum protection is provided for UDP data. UDPCKS(*YES) is the initial value.

*NO

Checksum protection is not provided for UDP data.

Path MTU discovery (IPPATHMTU)

Specifies whether the Path Maximum Transmission Unit (MTU) discovery function will be enabled on this system. Path MTU discovery allows for dynamic MTU adjustment, on a per connection basis, in order to maximize network throughput.

Single values

*SAME

The value does not change.

*NO

Path MTU discovery is not enabled for this system.

*DFT

The default path MTU discovery enablement status is *YES and the default path MTU discovery time interval is 10 minutes.

Element 1: Enablement

*YES

Path MTU discovery is enabled for this system.

Element 2: Interval

Specifies the amount of time, in minutes, that the TCP/IP protocol stack will cache the results of a path MTU discovery. When the time interval is exceeded, the path MTU is rediscovered.

*ONCE

Once a path MTU is discovered, it is not recalculated.

5-40320

Specify a path MTU discovery interval in minutes. Valid values range from 5 through 40320 minutes (28 days).

Notes:

1. In order for the path MTU discovery interval element to be specified, the first element must be set to *YES.
2. Path MTU discovery, if enabled, is only done over routes with a MTU value of *IFC.
3. The use of Path MTU discovery for UDP applications is controlled by individual sockets applications through the use of the SO_PATHMTU socket option.

IP datagram forwarding (IPDTGFWD)

Specifies whether the IP layer forwards Internet Protocol (IP) datagrams between different networks. It specifies whether the IP layer is acting as a gateway.

Note: IP does not forward datagrams between interfaces on the same subnet.

The IBM i implementation of TCP/IP does not include full gateway function as defined in RFC1009. A subset of the gateway functions are supported. One of the gateway functions supported is IP datagram forwarding capabilities.

*SAME

The value does not change.

*NO

IP datagrams are not forwarded. IPDTGFWD(*NO) is the initial value.

*YES

IP datagrams are forwarded.

IP source routing (IPSRCRTG)

The default setting for IP Source Routing (IPSRCRTG) is *YES or on. Some firewalls will not pass datagrams that have IP Source Routing switched on. This parameter allows you to switch IP Source Routing on or off as required for your situation.

*SAME

The value does not change.

*NO

The value *NO switches IP Source Routing off.

*YES

The value *YES switches IP Source Routing on. IPSRCRTG(*YES) is the initial value.

IP reassembly time-out (IPRSBTIMO)

Specifies, in seconds, the IP datagram reassembly time. If this time is exceeded, a partially reassembled datagram is discarded and an ICMP time exceeded message is sent to the source host.

*SAME

The value does not change.

*DFT

The default assembly time of 10 seconds is used.

5-120

Specify the number of seconds to be used for an IP reassembly time.

IP time to live (hop limit) (IPTTL)

Specifies the default TTL value. The IP datagram time-to-live value specifies a relative limit on the number of hops across which an IP datagram remains active. The time-to-live value acts as a "hop count" that is decremented by each gateway to prevent Internet routing loops.

Note: Even though this parameter is specified as a time-to-live value, it is not used as a time value. It is used as a counter. The standard description is time to live as specified in RFCs.

*SAME

The value does not change.

*DFT

The default time-to-live value of 64 is used.

Note: This default IP datagram time-to-live value is not used for datagrams sent to an IP multicast group address. The default IP datagram time-to-live value for datagram sent to an IP multicast group is always 1 as specified by the Internet standards. Individual multicast applications may override this default using the IP_MULTICAST_TTL socket option.

1-255

Specify an IP time-to-live value.

IP QoS enablement (IPQOSENB)

Specifies whether Quality of Service (QoS), IP Type of Service (TOS), or neither of the two are in use.

*SAME

The value does not change.

*TOS

Use TOS byte in the IP header.

*YES

Use QoS.

*NO

Do not use QoS or TOS. This is the initial value.

IP dead gateway detection (IPDEADGATE)

Specifies whether dead gateway detection will be enabled on this system. If traffic sent though the gateway is not acknowledged, the gateway will be polled to determine if it is active. If no reply to the polls is received then all routes using that gateway are deactivated. Gateways marked as dead will continue to be polled and when they respond again all routes using that gateway will be reactivated.

Single values

*SAME

The value does not change.

*NO

Dead gateway detection is not enabled for this system.

*DFT

The default dead gateway detection enablement status is *YES and the default dead gateway detection time interval is 2 minutes.

Element 1: Enablement

*YES

Dead gateway detection is enabled for this system.

*LINE

Dead gateway detection is enabled and operates independently for each line on this system.

Element 2: Interval

Specifies the amount of time, in minutes, that the TCP/IP protocol stack will wait between dead gateway polls. When the time interval is exceeded, the gateways are polled.

1-60

Specify a dead gateway poll interval in minutes.

Notes:

1. In order for the dead gateway detection interval element to be specified, the first element must be set to *YES.

ARP cache timeout (ARPTIMO)

Specifies, in minutes, the ARP cache time-out value. The time-out value's purpose is to flush out-of-date cache entries from the ARP cache.

*SAME

The value does not change.

*DFT

The default ARP cache time-out interval of 15 minutes is used.

1-1440

Specify an ARP cache time-out interval in minutes.

Enable ECN (ECN)

Specifies whether explicit congestion notification (ECN) is enabled.

If ECN is enabled, routers can notify end-nodes of congestion before queues overflow. Without ECN, end-nodes can only detect congestion when packets are lost due to queues overflowing.

*SAME

The value does not change.

*NO

ECN is not enabled for the system.

*YES

ECN is enabled for the system.

Network file cache (NFC)

Specifies whether the Network File Cache (NFC) function will be enabled on this system. The Network File Cache is used for the support of FRCA (Fast Response Cache Accelerator). FRCA dramatically improves the performance of serving non-secure static content by Web and other TCP servers.

Single values

*DFT

The default NFC enablement status is *YES with a default cache size of 10MB and a cache timeout of 300 seconds.

*CLEAR

Specifies to immediately clear the entire network file cache. After the cache is cleared, the previous Network File Cache values will be retained.

Element 1: Enablement

*SAME

The value does not change.

*YES

The Network File Cache is enabled for this system.

*NO

The Network File Cache is not enabled for this system.

Element 2: Cached file timeout

Specifies the maximum amount of time, in seconds, that a file can be cached in the Network File Cache. This ensures that a file is refreshed at a regular interval.

Note: A cache time can be specified when NFC is not enabled; however, the cache time will not take affect until NFC is enabled.

*SAME

The value does not change.

*NOMAX

The cached file entries will NOT timeout.

30-604800

Specify a file cache time in seconds. The maximum value of 604800 seconds equals 1 week.

Element 3: Cache size

Specifies the maximum amount of storage that may be used by the NFC for the entire system. This is the accumulative storage used by all TCP servers for loading files.

Note: A cache time can be specified when NFC is not enabled; however, the cache size will not take affect until NFC is enabled.

*SAME

The value does not change.

10-100000

Specify the number of megabytes to be used for the file cache size.

Log protocol errors (LOGPCLERR)

Specifies log protocol errors. This parameter enables a user to log protocol errors that occur during the processing of TCP/IP data. These TCP/IP stack layer functions use this parameter to determine if they log protocol-specific errors: IP, ICMP, ARP, and NAM. TCP and UDP do not log protocol errors.

The 7004 error reference code is logged when the LOGPCLERR(*YES) option is specified and inbound datagrams are silently discarded. Silently discarded means that an ICMP message is not returned to the originating host when a datagram is discarded because of header errors. Examples of such datagrams include those with invalid checksums and invalid destination addresses.

The error reference code is for information only. No action should be taken as a result of this error reference code. It is generated to assist with remote device or TCP/IP network problem analysis.

Note: These error conditions cannot be processed using an APAR.

The log protocol errors parameter should be used when error conditions require the logging of TCP/IP data, such as datagrams, to determine network problems.

The data is logged in the system error log. This error log is available through the Start System Service Tools (STRSST) command.

*SAME

The value does not change.

*NO

Protocol errors are not logged.

*YES

Protocol errors are logged.

DHCP unique identifier (DHCPUNQID)

Specifies the Dynamic Host Configuration Protocol (DHCP) unique identifier (refer to RFC 3315). This is a globally unique identifier used to identify clients and servers.

Single values

*SAME

The value does not change.

*GEN

The system will generate a new DHCP unique identifier. The system uses a link-layer address plus a timestamp to generate the identifier.

*DUID

*DUID indicates that Element 2 Current value is the current value of the DHCP unique identifier.

Element 1: Action

character-value

Specify *SAME to keep the system generated DHCP unique identifier or *GEN to have the system generate a new one.

Element 2: Current value

*PENDING

A DHCP unique identifier has not been generated yet. A new identifier will be generated the next time the system needs one.

hexadecimal-value

Displays the current value of the DHCP unique identifier. Changes to this value are ignored.

ICMPv6 error msg burst limit (IP6ERRLMT)

Specifies the maximum number of Internet Control Message Protocol for IPv6 (ICMPv6) error messages sent in a single burst.

*SAME

The value does not change.

*DFT

A maximum of 10 ICMPv6 error messages (the default) are sent in a single burst.

1-255

Specify the maximum number of ICMPv6 error messages to be sent in a single burst.

ICMPv6 error msg send rate (IP6ERRRATE)

Specifies the average rate limit of sending ICMPv6 error messages (in messages/second).

*SAME

The value does not change.

*DFT

An average of 10 ICMPv6 error messages per second are allowed to be sent.

1-255

Specify the average rate limit of sending ICMPv6 error messages.

IPv6 hop limit (IP6HOPLMT)

Specifies the limit on the number of hops across which an IPv6 datagram remains active.

*SAME

The value does not change.

*DFT

The maximum number of hops is 64.

1-255

Specify the maximum number of hops.

IPv6 dup route load sharing (IP6DUPRTLS)

Specifies how data traffic is distributed (load sharing) over duplicate IPv6 routes.

*SAME

The value does not change.

*DFT

The default value is used (*RTR).

*NONE

No load sharing is performed.

*RTR

Load sharing is done across routers on the same physical interface (line description).

IPv6 temp addr valid lifetime (IP6TMPAVL)

Specifies the valid lifetime (in days) of temporary addresses created as a result of privacy extensions for IPv6 stateless address auto-configuration.

*SAME

The value does not change.

*DFT

The default value is used (7 days).

.1-30

Specify the valid lifetime (in days).

IPv6 temp addr pref lifetime (IP6TMPAPL)

Specifies the preferred lifetime (in days) of temporary addresses created as a result of privacy extensions for IPv6 stateless address auto-configuration.

Note: IP6TMPAPL must specify a value less than or equal to IP6TMPAVL.

*SAME

The value does not change.

*DFT

The default value is used (1 day).

.1-30

Specify the preferred lifetime (in days).

IPv6 temp addr excluded prefix (IP6TMPAXP)

Specifies the IPv6 address prefixes that should not be used by stateless address auto-configuration when generating temporary addresses. Up to 5 prefixes and their associated lengths may be specified.

Single values

*SAME

The value does not change.

*DFT

The default value is used. Prefixes are not restricted.

Element 1: IPv6 prefix

character-value

Specify the IPv6 prefix to be excluded. The prefix is specified using the same syntax as an IPv6 address.

An IPv6 internet address is specified in the form x:x:x:x:x:x:x:x, where x is a hexadecimal number ranging from 0 through X'FFFF'. "::" may be used once in the IPv6 address to indicate one or more groups of 16 bits of zeros. The "::" may be used to compress leading, imbedded, or trailing zeros in the address.

If the prefix is entered from a command line, it must be enclosed in apostrophes.

Element 2: Address prefix length

1-64

Specify the length of the IPv6 prefix to be excluded.

IP QoS datagram batching (IPQOSBCH)

This parameter is no longer supported. It exists solely for compatibility with operating system releases earlier than Version 5 Release 3 Modification 0.

IP QoS timer resolution (IPQOSTMR)

This parameter is no longer supported. It exists solely for compatibility with operating system releases earlier than Version 5 Release 3 Modification 0.

Examples

Example 1: Using TCP/IP with UDP Checksum Verification

CHGTCPA   UDPCKS(*YES)

This command indicates that UDP checksumming is done for UDP data.

Example 2: Using Selected IP Parameters

CHGTCPA   IPDTGFWD(*YES)  IPTTL(5)  IPRSBTIMO(60)

This command indicates that TCP/IP has the following characteristics:

• IP datagrams are forwarded between interfaces on different subnets.
• IP time to live (TTL) is set to 5.
• IP reassembly time-out is set to 60 seconds.

Example 3: Using Selected TCP Parameters

CHGTCPA   TCPKEEPALV(100)  TCPURGPTR(*RFC)  TCPRCVBUF(16000)

This command indicates the following:

• TCP probes the other side of a connection every 100 minutes.
• The TCP urgent pointer in the TCP header points to the last byte of the urgent data (RFC convention).
• The TCP default receive buffer size is 16000 bytes.

Example 4: Turning Off IP Source Routing

CHGTCPA   IPSRCRTG(*NO)

This command indicates that IP source routing will no longer be allowed. Any IP datagrams found with IP source routing turned on will be rejected.

Example 5: Changing R1/R2 Counts and QoS Attributes

CHGTCPA   TCPR1CNT(3)  TCPR2CNT(10)  TCPCLOTIMO(300)
          IPQOSENB(*YES) IPDEADGATE(*YES)

This command indicates the following:

• TCP is set to request a different network route after 3 unacknowledged transmissions.
• TCP is set to stop retransmitting an unacknowledged packet after 10 unsuccessful attempts.
• TCP is set to wait 300 seconds (5 minutes) before reusing a closed connection socket pair.
• Quality of Service (QoS) is enabled.
• Dead gateway detection is enabled.

Error messages

*ESCAPE Messages

CPF9801

Object &2 in library &3 not found.

CPF9802

Not authorized to object &2 in &3.

CPF9803

Cannot allocate object &2 in library &3.

CPF9807

One or more libraries in library list deleted.

CPF9808

Cannot allocate one or more libraries on library list.

CPF9810

Library &1 not found.

CPF9820

Not authorized to use library &1.

CPF9830

Cannot assign library &1.

TCP1D03

&1 member record length not correct.

TCP1D04

Error occurred processing member &1 of &2/&3.

TCP15A3

TCP/IP attributes not changed.

TCP15A5

Error accessing member &3

TCP15A6

Attribute file keyword &4 missing

TCP15A7

Attribute file keyword &4 not valid.

TCP8050

*IOSYSCFG authority required to use &1.

TCP9503

File &3 in library &2 not available.

TCP9999

Internal system error in program &1.