| Where allowed to run: All environments (*ALL) Threadsafe: No |
Parameters Examples Error messages |
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 default values for the keywords follow. These values are also used if *DFT is specified for the keyword.
Restriction:
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| Keyword | Description | Choices | Notes |
|---|---|---|---|
| TCPKEEPALV | TCP keep alive | 1-40320, *SAME, *DFT | Optional |
| TCPURGPTR | TCP urgent pointer | *SAME, *BSD, *RFC | Optional |
| TCPRCVBUF | TCP receive buffer size | 512-8388608, *SAME, *DFT | Optional |
| TCPSNDBUF | TCP send buffer size | 512-8388608, *SAME, *DFT | Optional |
| TCPR1CNT | TCP R1 retransmission count | 1-15, *SAME, *DFT | Optional |
| TCPR2CNT | TCP R2 retransmission count | 2-16, *SAME, *DFT | Optional |
| TCPMINRTM | TCP minimum retransmit time | 100-1000, *SAME, *DFT | Optional |
| TCPCLOTIMO | TCP time-wait timeout | 0-14400, *SAME, *DFT | Optional |
| TCPCNNMSG | TCP close connection message | *SAME, *THRESHOLD, *ALL, *NONE | Optional |
| UDPCKS | UDP checksum | *SAME, *YES, *NO | Optional |
| IPPATHMTU | Path MTU discovery | Single values: *SAME, *DFT, *NO Other values: Element list |
Optional |
| Element 1: Enablement | *YES | ||
| Element 2: Interval | 5-40320, *ONCE | ||
| IPDTGFWD | IP datagram forwarding | *SAME, *YES, *NO | Optional |
| IPSRCRTG | IP source routing | *SAME, *YES, *NO | Optional |
| IPRSBTIMO | IP reassembly time-out | 5-120, *SAME, *DFT | Optional |
| IPTTL | IP time to live (hop limit) | 1-255, *SAME, *DFT | Optional |
| IPQOSENB | IP QoS enablement | *SAME, *TOS, *YES, *NO | Optional |
| IPDEADGATE | IP dead gateway detection | Single values: *SAME, *DFT, *NO Other values: Element list |
Optional |
| Element 1: Enablement | *YES | ||
| Element 2: Interval | 1-60 | ||
| ARPTIMO | ARP cache timeout | 1-1440, *SAME, *DFT | Optional |
| ECN | Enable ECN | *SAME, *YES, *NO | Optional |
| NFC | Network file cache | Single values: *DFT, *CLEAR Other values: Element list |
Optional |
| Element 1: Enablement | *SAME, *YES, *NO | ||
| Element 2: Cached file timeout | 30-604800, *SAME, *NOMAX | ||
| Element 3: Cache size | 10-100000, *SAME | ||
| LOGPCLERR | Log protocol errors | *SAME, *YES, *NO | Optional |
| IPQOSBCH | IP QoS datagram batching | *SAME, *NORMAL, *MINDELAY | Optional |
| IPQOSTMR | IP QoS timer resolution | 5-5000, *SAME, *DFT | Optional |
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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 Sockets Programming information in the iSeries Information Center at http://www.ibm.com/eserver/iseries/infocenter.
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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.
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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. Decreasing this value may improve performance in situations where many retransmissions occur due to the overrunning of a network adapter.
Notes:
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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:
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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.
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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.
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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.
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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.
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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:
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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).
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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
Element 1: Enablement
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.
Notes:
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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 i5/OS 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.
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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.
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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.
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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.
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.
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Specifies whether Quality of Service (QoS), IP Type of Service (TOS), or neither of the two are in use.
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Specifies whether dead gateway detection will be enabled on this system. Dead gateway detection is a mechanism which involves polling all attached gateways. If no reply is received to the polls then all routes using that gateway are inactivated. Gateways marked as dead will continue to be polled and when they respond again all routes using that gateway will be reactivated.
Single values
Element 1: Enablement
Element 2: Interval
Specifies the amount of time, in minutes, that the TCP/IP protocol stack will wait between dead gateway detection polls. When the time interval is exceeded, the gateways are polled.
Notes:
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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.
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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.
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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
Element 1: Enablement
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.
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.
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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.
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This parameter is no longer supported. It exists solely for compatibility with releases earlier than Version 5 Release 3 Modification 0 of i5/OS.
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This parameter is no longer supported. It exists solely for compatibility with releases earlier than Version 5 Release 3 Modification 0 of i5/OS.
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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:
Example 3: Using Selected TCP Parameters
CHGTCPA TCPKEEPALV(100) TCPURGPTR(*RFC) TCPRCVBUF(16000)
This command indicates the following:
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:
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*ESCAPE Messages
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