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