Wireshark mailing list archives
Re: Window scaling
From: Jim Aragon <Jim () agdatasystems com>
Date: Wed, 01 Jun 2016 12:01:58 -0700
At 11:26 AM 6/1/2016, Chris Maynard wrote: >Robert Dahlem <Robert.Dahlem@...> writes: >> But my Wireshark 1.12.8 tells me "Calculated window size: 8192" which >> would match with the firewalls behaviour. >> >> Is there something wrong with the SYN/ACK packet? > >No, there's nothing wrong with the SYN/ACK packet, at least as far as >I can tell. SYN packets are never themselves scaled so Wireshark will >always display the calculated window size the same as the window size >value, regardless of the scaling factor. > >What's missing here though is the client's SYN packet showing its >scaling factor, but I suspect that the client does not support >scaling, which means there is no window scaling effect in either direction.Well, we can conclude that the client does support window scaling because if the client does not announce a scale factor in its SYN packet, the server won't announce window scaling in the SYN/ACK, since there's no point to doing so. From RFC 7323: "Furthermore, the Window Scale option will be sent in a <SYN,ACK> segment only if the corresponding option was received in the initial <SYN> segment."
As Chris pointed out, packets with the SYN bit set are never scaled, so the window size value and the calculated window size are the same, but f you look farther down in the captured packets, past the SYN and SYN/ACK, you will see that the calculated window size is the number in the window size value field multiplied by the scale factor.
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Current thread:
- Window scaling Robert Dahlem (Jun 01)
- Re: Window scaling Maynard, Chris (Jun 01)
- Message not available
- Re: Window scaling Jim Aragon (Jun 01)
- Re: Window scaling Robert Dahlem (Jun 06)
- Re: Window scaling ronnie sahlberg (Jun 06)
- Re: Window scaling Robert Dahlem (Jun 06)
- Re: Window scaling ronnie sahlberg (Jun 06)
- Re: Window scaling Lee (Jun 06)
- Message not available
- Re: Window scaling Maynard, Chris (Jun 01)