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Community Member

Question on windowing

I just got hit with a troubleshooting question today, and didn't know how to answer. What does it mean when a packet has a window size of 0? TIA.

Rich

3 REPLIES
Community Member

Re: Question on windowing

It's called "closing the window" and is usually sent by a device that is getting TCP information much faster than it can respond to. It probably was prefaced by a shrinking of the window first.

I have usually seen it with overtaxed servers.

Dave

Super Bronze

Re: Question on windowing

The receiving host is informing the sending host it's unable to accept any additional data. If this is seen, it's likely the receiving host does have some buffer space but is trying to avoid the TCP "silly window syndrome".

[edit]

The reason for this happening is the receiving host can't keep up with the sending host's tranmission rate. This shouldn't be common since most network media is generally "slower" compared to processing performance of most modern hosts. However, as also noted by Dave, a very busy host might be unable to keep up with incoming network data.

Community Member

Re: Question on windowing

Thanks Joe & Dave. Excellent explanations.

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