Wireshark mailing list archives
Re: Windows 7 Ignores TCP MSS?
From: Hansang Bae <for_list_hbae () nyc rr com>
Date: Wed, 23 Mar 2011 20:09:13 -0400
On 3/23/2011 7:14 PM, Robinson, Eric wrote:
I just did a capture of a file transfer from a Windows 7 computer to a Linux FTP server. I can see the Windows client reporting its MSS at 1460. Then I see the FTP server reporting its MSS at 1460. But when the transfer starts, the client sends 2896-byte packets!Following are the settings on the Windows client box. C:\>netsh interface ipv4 show subinterface MTU MediaSenseState Bytes In Bytes Out Interface ------ --------------- --------- --------- -------------4294967295 1 0 22655 Loopback Pseudo-Interface 11500 1 271689236 1374564858 Local Area Connection C:\>netsh int tcp show global TCP Global Parameters ---------------------------------------------- Receive-Side Scaling State : enabled Chimney Offload State : disabled NetDMA State : enabled Direct Cache Acess (DCA) : disabled Receive Window Auto-Tuning Level : disabled Add-On Congestion Control Provider : ctcp ECN Capability : disabled RFC 1323 Timestamps : disabled
It's likely that the NIC has hardware TCP offloading enabled and you're capturing it before the NIC chops it up to 1460. If you capture the traffic from the network, you'll likely see the 1460 TCP length packets.
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Current thread:
- Windows 7 Ignores TCP MSS? Robinson, Eric (Mar 23)
- Re: Windows 7 Ignores TCP MSS? Hansang Bae (Mar 23)
- Re: Windows 7 Ignores TCP MSS? Robinson, Eric (Mar 23)
- Re: Windows 7 Ignores TCP MSS? Andrew Hood (Mar 24)
- Re: Windows 7 Ignores TCP MSS? Robinson, Eric (Mar 23)
- Re: Windows 7 Ignores TCP MSS? Hansang Bae (Mar 23)