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I am using macOS 11.4 and padavan firmware on the router. It's quite slow (a few to tens of seconds) when I connect to the router's admin page from macOS, and tcpdump showed that a lot of tcp connections are stuck at the first handshake, the router didn't reply with SYN/ACK after macOS sent SYN.

There's no such problem when I connect to the router from another device or visit another website from macOS.

Are there special options/headers from macOS' tcp package?

00:48:25.374383 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083099 ecr 0,sackOK,eol], length 0
00:48:25.475394 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083200 ecr 0,sackOK,eol], length 0
00:48:25.576576 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083301 ecr 0,sackOK,eol], length 0
00:48:25.677740 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083402 ecr 0,sackOK,eol], length 0
00:48:25.778906 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083503 ecr 0,sackOK,eol], length 0
00:48:25.879255 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083603 ecr 0,sackOK,eol], length 0
00:48:26.080421 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596083804 ecr 0,sackOK,eol], length 0
00:48:26.481605 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596084205 ecr 0,sackOK,eol], length 0
00:48:27.283921 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596085006 ecr 0,sackOK,eol], length 0
00:48:28.885169 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1596086607 ecr 0,sackOK,eol], length 0
00:48:32.086355 IP mbp.lan.59304 > router.lan.http: Flags [S], seq 1796724219, win 65535, options [mss 1460,sackOK,eol], length 0
00:48:32.099170 IP router.lan.http > mbp.lan.59304: Flags [S.], seq 4020057176, ack 1796724220, win 14600, options [mss 1460,nop,nop,sackOK], length 0
00:48:32.099295 IP mbp.lan.59304 > router.lan.http: Flags [.], ack 1, win 65535, length 0
00:48:33.432798 IP mbp.lan.59304 > router.lan.http: Flags [P.], seq 1:2, ack 1, win 65535, length 1: HTTP
00:48:33.466137 IP router.lan.http > mbp.lan.59304: Flags [.], ack 2, win 14600, length 0

1 Answer 1

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It is very vague to say whether or not something is "special". If you're asking if there's something non-standard or invalid about the options/headers from macOS' TCP package - then the answer is no.

You have used the program tcpdump to produce the packet listing in your question. You could increase the verbosity of that program (-vvvv) to see more information about the actual header contents. You could also tell it to show the actual payload of the packets in order to examine any differences there.

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