Finisar Surveyor manual TCP Fast Retransmission

Surveyor

User’s Guide

TCP Fast Retransmission

Counter

TCP Fast Retransmission is a counter of all TCP retransmissions that are less than a threshold value. A count of all TCP Fast Retransmissions displays in the Overview counters of Expert View. A threshold for this counter can be set in Expert Alarms.

Expert Symptom

TCP Fast Retransmission events are automatically logged as expert symptoms. The Symptom Summary field provides the IP addresses of the client and server involved. For example:

In 5 ms (< 100 ms) between [206.250.228.69]/[TCP/IP

WKP:1988] and [206.250.228.11]/[SMTP]

Diagnostic Details

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Problem Description:

A TCP/IP packet has been retransmitted. There was no ACK form the receiver, causing the sender to retransmit the packet. And the time from the last transmission is less than the threshold value.

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Probable Cause(s):

1.An ACK sent by the receiver was lost.

2.The network is overloaded.

3.The path to the receiving station has long delays.

4.There may be a problem with the receiver’s TCP/IP stack.

5.There may be a problem with the sender’s TCP/IP stack.

6.There may be an overloaded switch or router.

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Recommended Action(s):

1.Load balance your network.

2.If you see repeated delays and too many retransmissions, your router or switch may need upgrading.

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