amd64 tcp weirdness

Jacco Braat jacco at
Tue Dec 5 09:31:47 PST 2006


i'm using RELENG_6 on amd64 and have trouble with downloads.

I think this is related to the window scaling feature.

generates 5 packets for the HTTP GET request, and lots of DUP ACK packets.
there is no Window Scale option in the SYN ACK reply.

generates only 1 packet for the HTTP GET request.
Window Scale = 0 in the SYN ACK reply

on i386 also RELENG_6 no such differences.

setting net.inet.tcp.recvspace to a smaller value also gives normal results.

I noticed this behavior because my Realtek 8168B got stuck on some
websites, a Intel Pro/1000 did not. With both cards the tcpdumps are


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