TCP Retransmissions.

Network protocols
Hi, I am trying to troubleshoot poor telnet performance over our WAN, and have come up against a figure for re-transmits that I consider to be too high. Looking at the device, the re-transmits are currently 7.5% of all segments sent. I have looked at another device to try and get a feel for an acceptable level, and see figures of <1%. My question is : Is 7.5% too high and very likely to be the cause of my poor performance, or have I just happened to stumble on a really good connection running at <1%.? Any help is appreciated. Regards Degz.

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A retransmit value of 7.5% may not be too high by all standards, but depending on your network infrastucture may be indicative of a problem. You stated having decreased performance using the Telnet, have you compared retransmit values using another protocol such as ftp? Is your problem related to a specific device or all devices attached to your network? A specific time of day? Does it occurr internally or outside of your network? Do you telnet accross a router?

These are a few questions you may want to answer first in troubleshooting this issue. You may find that 7.5% is an expected value or you may uncover a bottleneck.

Good Luck

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  • DerekKing
    Hi, Thanks for the ideas. The problem is related to a specific device linked over 2 routers.(Head Office to Remote Site over private serial link. ) The device is an IP to Serial converter at the remote site that is experiencing this 7.5% re-transmits. In checking today, all other devices on the affected subnet appear OK. Users complain of slowdowns at different times of the day, and not everyday. I haven't yet figured if these values are increasing at the point of slowdowns. Cheers Degz.
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  • Bobkberg
    Have you logged into the router(or used an SNMP application) to look at what the statistics and error counts are on the respective interfaces at each end, as well as in the middle (if appropriate)? If the immediate investigation yields nothing obvious, I'd suggest that you set up an MRTG system (You should have one anyway) to monitor ALL key variables on the WAN links. You might also want to set up SmokePing on the same system to monitor latency. They're both free - and written by Tobias Otiker. And consider contributing to his CD/DVD fund. See his web site for details. Bob
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