Network Visibility Agents can calculate an extensive set of metrics based on the TCP flows observed by the Network Agents. In addition to KPI, PIE, and Troubleshooting metrics, you can view advanced metrics for network elements of interest (tiers, nodes, links, and connections) in the Metric Browser. Using time-based charts, you can detect and analyze these behavior traits: To view advanced network metrics, open the Metric Browser and navigate to Application Infrastructure Performance. The Metric Browser shows connection/flow metrics for the following aggregations (highlighted in red): # Client Limited The number of TCP window updates sent by a client node indicating that it is receiving data at a faster rate than the application can process # Client Zero Window If a client's TCP buffer is full, it sends Zero as the TCP receive window size to indicate that it cannot receive more data. The data transfer then stops until the client can process the data in its buffer. A high rate of Client TCP Zero Window messages indicates a problem with either: # Connection Errors The sum of Syn Resets + Syn Blackholes + TCP Resets - Established # Connection Requests # Current Established Connections # Data Retransmits # Delayed Acks (Data Piggy Back) # Delayed Acks (Timeouts) The average number of times a receiving node sent an ACK (acknowledgment) because the Delayed ACK timer expired This is a "worst-case" delay for the Delayed ACK algorithm and occurs most often when Nagle's algorithm and Delayed ACK are enabled on the sending and receiving node, respectively. A high rate of delayed ACKs may contribute significantly to the average Latency on a Connection. # Errors # Fin Errors The number of errors generated while tearing down the connections (TCP FIN errors). Many connections in FIN wait states can cause delays in creating new connections. # Flows (<1KB) # Flows (1k - 10k) # Flows (10k - 100k) # Flows (100k-1MB) # Flows (1MB - 10MB) # Flows (>10MB) Use these metrics to analyze the distribution of flows by throughput # Flows - Handshake (1SD) # Flows - Handshake (2SD) # Flows - Handshake (3SD) Under ideal conditions, all flows should be within 1SD of the average # Flows - Lifetime (1SD) # Flows - Lifetime (2SD) # Flows - Lifetime (3SD) Under ideal conditions, all flows should be within 1SD of the average. 2SD or 3SD flows indicate inconsistent flow treatment along the network path. These inconsistencies can occur when a network service decreases the available bandwidth intentionally (bandwidth throttling) or prioritizes some types of traffic over others (traffic shaping). Short-lived connections, even if they are intermittent, may indicate an issue worth investigating. The more short-lived connections get generated, the more resources are spent setting up and tearing down these connections. # Flows - RTT (1SD) # Flows - RTT (2SD) # Flows - RTT (3SD) Number of flows whose Round Trip Times are 1, 2, or 3 Standard Deviations higher than the average for all flows in the parent group. Under ideal conditions, all flows should be within 1SD of the average. High-RTT connections, even if they are intermittent, may indicate an issue worth investigating. If the average response time for an eCommerce web app is two seconds (acceptable), but 5% of transactions are 20 seconds or higher (not acceptable), this can result in a significant number of unhappy customers and lost revenue. # Flows - TCP Data Rxmt # Flows - TCP Resets The average number of flows that were closed by a TCP Reset # Flows - w/o TCP SACK Number of flows with the TCP Selective Acknowledgment (SACK) option disabled. With SACK enabled, a receiver can send SACK packets to acknowledge receipt of multiple data packets in the case of lost segments. This improves network performance by reducing the number of retransmissions. With SACK disabled, the receiver must resend all the packets after the last lost segment, even if they were received by the peer. # Flows - w/o TCP Timestamp # IP Fragment Count # Loss Pkts # Nagle Delays The number of times a message-send event was delayed because the sending node had to wait for previously-sent data to be acknowledged (ACK'd). This occurs most often when Nagle's algorithm and Delayed ACK are enabled on the sending and receiving node, respectively. # PIE Events Use Performance Impacting Elements (PIE) to identify the location of actual or potential bottlenecks: Retransmission Timeouts (RTOs) indicate network packet loss which results in retransmission of data when the TCP retransmission timer expires (Timer to make sure data is ACK'ed) # SACK Retransmits # Server Limited The number of TCP window updates sent by a server node indicating that it is receiving data at a faster rate than the application can process # Server Zero Window If a server's TCP buffer is full, it sends Zero as the TCP receive window size to indicate that it cannot receive more data. The data transfer then stops until the server can process the data in its buffer. A high rate of Server TCP Zero Window messages indicates a problem with either: # Syn Blackholes The number of connection attempts that went unanswered and resulted in a failure. Syn blackholes can severely impact application performance. # Syn Resets The number of connection attempts that were explicitly refused by the other host. Syn resets can severely impact application performance. # TCP Resets - Established The average number of times an established TCP flow was reset # TCP Resets - Fin # TTL Changes (1 - 2 hops) # TTL Changes (3 - 4 hops) # TTL Changes (>=5 hops) The number of routing-hop changes experienced by this connection. Frequent variations in routing-hop changes indicate routing problems in the network and can severely affect app performance. Under ideal conditions, the number of hops should be consistent. Avg # TTL Hops Delayed Acks Lag (usec) Initial RTT (usec) Round trip time for the initial two SYN packets (between SYN and SYN-ACK, or SYN-ACK and ACK depending upon whether the Agent is running on client or server) Latency - RTT (usec) Average round-trip latency (from packet transmission to acknowledgment) for all packets Lifetime (usec) Loss (per mille) Nagle Delays Lag (usec) Pkts per Sec Rx Pkts per Sec Rx Throughput (BPS) TCP Handshake (usec) Round trip time for the initial three-way connection setup for all flows in the parent group: Throughput (BPS) Tx Pkts per Sec Tx Throughput (BPS)Viewing TCP Flow Metrics
TCP Flow Metric Descriptions
Default Monitoring Mode KPI KPI KPI The total number of connection requests (successful and unsuccessful) sent during the selected time window KPI The number of established (setup) flows/connections KPI Number of TCP data packets that were retransmitted for all TCP Connections KPI The average number of times a receiving node sent an ACK (acknowledgment) by "piggybacking" the ACK onto another message Advanced Advanced The number of TCP messages sent indicating an error in setting up the connection (SYN errors), or tearing down the connection (FIN errors) KPI KPI Advanced The number of TCP flows with connection-setup times that are 1, 2, or 3 Standard Deviations outside (higher or lower than) the average for that connection group Advanced The number of TCP flows with lifetimes that are 1, 2, or 3 Standard Deviations outside (higher or lower than) the average. Advanced Advanced Number of flows within which any packet was retransmitted. Retransmissions are an indication of packet loss. Advanced KPI Advanced Number of flows with the TCP Timestamp option disabled. Use this option to calculate more accurate Round Trip Times. Advanced The total number of IP fragments attributes to this TCP connection group. A high level of fragmentation indicates network issues which can severely affect application performance. KPI The total number of packets that were lost (sent but never received) Advanced Advanced KPI # RetransmissionTimeouts
KPI Average number of packets that were retransmitted due to a SACK message that indicated an unreceived packet KPI KPI KPI KPI KPI KPI The average number of times a TCP flow was reset while it was in the process of getting closed KPI Advanced The average number of routing-hop changes experienced by this connection Advanced The average amount of lag that Delayed ACKs are adding to the overall Latency of the Connection Advanced KPI KPI Average lifetime (from initial setup to final teardown) for TCP sessions in the Connection group KPI The number of packets lost per 1000 packets sent. "Per mille" is a percentage with one additional digit of precision. KPI The average amount of lag that Nagle delays are adding to the overall Latency of the Connection Advanced Average rate of packets sent and received KPI Average rate of packets received Advanced Average rate of bytes received Advanced KPI Throughput (bytes per second) for the application of interest on all TCP sessions KPI Rate of packets sent Advanced Rate of traffic received Advanced
Metric Name
Description and Notes
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