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acknowledgement number in tcp header
I figured this out myself. The ack number reported by tcpdump is not the same as the one in the tcp packet. To see the real ack number you need to use tcpdump -S. By default tcpdump shows "relative" sequence/ack numbers because they are easier to read presumably. -
acknowledgement number in tcp header
Here are a sequence of tcp packets I captured using tcpdump: 10:47:27.784044 IP (tos 0x0, ttl 63, id 33239, offset 0, flags [DF], proto: TCP (6), length: 60) 192.168.100.154.51509 > 10.0.0.4.80: S, cksum 0x6f22 (correct), 4274988216:4274988216(0) win 5840 <mss 1460,sackOK,timestamp 4892015...
