eG Monitoring
 

Measures reported by CtxNsTcpRetTest

Due to network congestion, traffic load balancing, or other unpredictable network behavior, IP packets can be lost. TCP detects these problems, and requests retransmission of lost data. Most often TCP retransmissions have a significant impact on application performance, and will hence have to be kept at a minimum. Using this test, you can determine how often packets sent to/sent by the NetScaler were retransmitted, and can promptly detect the following:

  • What type of packets (Client, Server, SYN, FIN, etc.) were retransmitted the most?
  • What is causing the retransmissions - is it a bad network link between the NetScaler appliance and the virtual server? is it a poor network connection between the client and the NetScaler appliance? or is it due to an improperly set timeout value for TCP connections?
  • Were the retransmissions successful?

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
Clt_retrans Indicates the number of packets that were retransmitted by a client during the last measurement period. Number The packets are retransmitted when the acknowledgment from the NetScaler has not reached the client.
Svr_retrans Indicates the number of packets that were retransmitted by a server during the last measurement period. Number The packets are retransmitted when the acknowledgment from the NetScaler has not reached the server.
Full_packet_retrans Indicates the number of full packets (i.e., the packets as it was originally transmitted) retransmitted by the client or the server during the last measurement period. Number  
Partial_packet_retrans Indicates the number of partial packets that were retransmitted by a client or server during the last measurement period. Number Some packets may be lost/dropped during transmission due to network congestion or due to a possible connection failure. When retransmission takes place, the remaining packets will alone be sent by the client/server and such remaining packets are termed as partial packets.
Syn_packets_retries Indicates the number of SYN (synchronize) packets resent to a server during the last measurement period. Number  
Fin_packets_retries Indicates the number of FIN packets resent to a server or client during the last measurement period. Number  
Syn_packets_timeout Indicates the number of SYN packets that were not retransmitted during the last measurement period. Number The SYN packets may not be retransmitted due to the timeout that occurred while establishing a connection on the NetScaler.
Fin_packets_timeout Indicates the number of FIN packets that were not retransmitted even after four attempts during the last measurement period. Number The FIN packets may not be transmitted due to the connection timeout that may have occurred because of not receiving the ACK packet after retransmitting the FIN packet four times.
Tcp_retrans Indicates the number of TCP packets retransmitted during the last measurement period. Number Ideally, the value of this measure has to be low.
Tcp_retrans_timeout Indicates the number of times the NetScaler terminates a connection due to non-retransmission of the packets even after seven attempts on that connection during the last measurement period. Number If the value of this measure is high, you may want to check what is causing the repeated transmission failures.
Fast_retrans Indicates the number of TCP packets on which the NetScaler performs a fast retransmission in response to three duplicate acknowledgements or a partial acknowledgement during the last measurement period. Number Fast retransmission occurs because the NetScaler assumes that the packet is lost and retransmits the packet before its time-out.
Tcp_level_cip_fail Indicates the number of times the TCP level client header insertion failed during the last measurement period. Number  
First_retrans Indicates the number of packets that were retransmitted in the first attempt by the NetScaler during the last measurement period. Number If a large number of packets take too long to be successfully retransmitted, you may have to figure out what is causing the repeated retransmission failures and fix it before more packet loss occurs.
Second_retrans Indicates the number of packets that were retransmitted in the second attempt by the NetScaler during the last measurement period. Percent
Third_retrans Indicates the number of packets that were retransmitted in the third attempt by the NetScaler during the last measurement period. Number
Forth_retrans Indicates the number of packets that were retransmitted in the fourth attempt by the NetScaler during the last measurement period. Number
Fifth_retrans Indicates the number of packets that were retransmitted in the fifth attempt by the NetScaler during the last measurement period. Number
Sixth_retrans Indicates the number of packets that were retransmitted in the sixth attempt by the NetScaler during the last measurement period. Number
Seventh_retrans Indicates the number of packets that were retransmitted in the seventh attempt by the NetScaler during the last measurement period. Number
Bad_check_sum Indicates the number of packets that are received with TCP checksum errors. Number  
Data_after_fin Indicates the number of bytes received following a connection termination request. Number This error is usually caused by reordering packets during transmission.
Syn_in_syn_rcvd Indicates the number of SYN packets received on a connection that is in the SYN_RCVD state. Number A connection goes into the SYN_RCVD state after receiving a SYN packet.
Syn_in_est Indicates the number of SYN packets received on a connection that is in the ESTABLISHED state. Number A SYN packet is not expected on an ESTABLISHED connection.
Syn_sent_bad_ack Indicates the number of incorrect ACK packets received on a connection that is in the SYN_SENT state. Number An incorrect ACK packet is the third packet in the three-way handshake that has an incorrect sequence number.
Tcp_rst Indicates the number of reset packets received from a client or a server. Number  
Tcp_rst_non_est Indicates the number of reset packets received on a connection that is not in the ESTABLISHED state. Number  
Rst_out_of_window Indicates the number of reset packets received on a connection that is out of the current TCP Window. Number  
Rst_in_time_wait Indicates the number of reset packets received on a connection that is in the TIME_WAIT state. Number Typically, packets cannot be transferred on a connection in the TIME_WAIT state. Therefore, the value of this measure is desired to be very low.
Clt_out_of_order Indicates the number of out of order TCP packets received from a client. Number Typically, packets cannot be transferred on a connection in the TIME_WAIT state. Therefore, the value of this measure is desired to be very low.
Svr_out_of_order Indicates the number of out of order TCP packets received from a server. Number
Clt_hole Indicates the number of TCP holes created on a client connection. Number TCP holes are created on the NetScaler appliance for each group of missing packets when out of order packets are received from a client.
Svr_hole Indicates the number of TCP holes created on a server connection. Number TCP holes are created on the NetScaler appliance for each group of missing packets when out of order packets are received from a server.
Cookie_pkt_seq_rej Indicates the number of SYN cookie packets rejected due to an incorrect sequence number. Number  
Cookie_pkt_sig_rej Indicates the number of SYN cookie packets rejected due to an incorrect signature. Number  
Cookie_pkt_seq_drop Indicates the number of SYN cookie packets dropped because the sequence number specified in the packets is outside the current Window. Number  
Cookie_pkt_mss_rej Indicates the number of SYN cookie packets rejected due to the incorrect maximum segment size (MSS) specified in the packets. Number  
Ip_port_fail Indicates the number of port allocations failed on a mapped IP address. Number These failures occur when the maximum limit of 65536 has exceeded or the mapped IP address is not configured.
Any_port_fail Indicates the number of port allocations that failed on a subnet IP address or virtual server IP address. Number These kind of failures occur when the maximum limit of 65536 has exceeded.
Stray_pk Indicates the number of packets received on a connection whose state is not maintained on the NetScaler appliance. Number  
Sent_rst Indicates the number of reset packets that are sent to a client or a server. Number  
Bad_state_conn Indicates the number of connections that are not in a valid TCP state. Number  
Rst_threshold Indicates the number of reset packets dropped due to the violation in default threshold. Number If the value of this measure increases gradually/suddenly, administrators should reconfigure the default threshold value using the set rate Control command.
Out_of_window_pkts Indicates the number of packets received which are out of the current advertised Window. Number  
Syn_dropped_cong Indicates the number of SYN packets dropped due to network congestion. Number