Date: Fri, 15 Apr 2022 21:24:20 +0200 From: tuexen@freebsd.org To: Florian Smeets <flo@smeets.xyz> Cc: current@freebsd.org Subject: Re: IPv6 TCP: first two SYN packets to local v6 unicast addresses ignored Message-ID: <E0584477-0F2E-454D-871C-368F14A9AF1D@freebsd.org> In-Reply-To: <131c363a-7b7d-a106-5b8a-6838e7a66567@smeets.xyz> References: <131c363a-7b7d-a106-5b8a-6838e7a66567@smeets.xyz>
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> On 15. Apr 2022, at 20:20, Florian Smeets <flo@smeets.xyz> wrote: >=20 > [bcc to net@ for wider exposure] >=20 > Hi, >=20 > there seems to be an issue with local IPv6 TCP connections on main. I = have been seeing this for a couple of months at least. pkg upgr on my = webserver hosting the pkg repo is very slow, all other hosts can connect = to the pkg repo just fine. So IPv6 connections from external hosts are = not affected. >=20 > I thought I must have misconfigured something, as my setup is a bit = weird. Yesterday I noticed the same issue on a different host, turns out = all my 14.0 hosts seem to be affected, cognet@ could also reproduce it = on one of his systems. >=20 > The service/software used does not seem to matter, I tried with port = 22, 25, 80 and 443. >=20 > ICMP and UDP don't seem to be affected. ping6 gets replies = immediately. And UDP connections with nc -l -u / nc -u don't have any = delay, sent data is received immediately. >=20 > Testing local TCP connections show this: >=20 > flo@rp64:~ $ ifconfig dwc0|grep 2003 > inet6 2003:cf:df49:c97:4c59:ebff:fec1:463d prefixlen 64 autoconf > flo@rp64:~ $ nc -v 2003:cf:df49:c97:4c59:ebff:fec1:463d 22 > [3 second delay here] > Connection to 2003:cf:df49:c97:4c59:ebff:fec1:463d 22 port [tcp/ssh] = succeeded! > SSH-2.0-OpenSSH_8.9 FreeBSD-20220413 >=20 > tcpdump on lo0 shows that the first two SYN packets are ignored / time = out, then the connection is successfully established. >=20 > 19:28:38.685128 IP6 2003:cf:df49:c97:4c59:ebff:fec1:463d.61294 > = 2003:cf:df49:c97:4c59:ebff:fec1:463d.22: Flags [S], seq 2489479594, win = 65535, options [mss 16324,nop,wscale 6,sackOK,TS val 3410505643 ecr 0], = length 0 >=20 > 19:28:39.696047 IP6 2003:cf:df49:c97:4c59:ebff:fec1:463d.61294 > = 2003:cf:df49:c97:4c59:ebff:fec1:463d.22: Flags [S], seq 2489479594, win = 65535, options [mss 16324,nop,wscale 6,sackOK,TS val 3410506654 ecr 0], = length 0 >=20 > 19:28:41.897836 IP6 2003:cf:df49:c97:4c59:ebff:fec1:463d.61294 > = 2003:cf:df49:c97:4c59:ebff:fec1:463d.22: Flags [S], seq 2489479594, win = 65535, options [mss 16324,nop,wscale 6,sackOK,TS val 3410508856 ecr 0], = length 0 >=20 > 19:28:41.897907 IP6 2003:cf:df49:c97:4c59:ebff:fec1:463d.22 > = 2003:cf:df49:c97:4c59:ebff:fec1:463d.61294: Flags [S.], seq 2857552476, = ack 2489479595, win 65535, options [mss 16324,nop,wscale 6,sackOK,TS val = 1858349482 ecr 3410508856], length 0 >=20 > 19:28:41.897962 IP6 2003:cf:df49:c97:4c59:ebff:fec1:463d.61294 > = 2003:cf:df49:c97:4c59:ebff:fec1:463d.22: Flags [.], ack 1, win 1276, = options [nop,nop,TS val 3410508856 ecr 1858349482], length 0 >=20 > I need help debugging this, I don't know how to analyze this further. = I will start bisecting this, but I thought maybe someone has an idea. Hi Florian, I can reproduce this locally, will try to figure out what is going on. = If you can bisect it, it would be great. Best regards Michael >=20 > Thanks, > Florian > <OpenPGP_0xEF5BA4DCD5A9F3C0.asc>
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