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Old 18th January 2020
k2k k2k is offline
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Join Date: Jan 2020
Posts: 2
Default TCP DNS problem

Hello,

Could anyone help me to debug the problem ?

I have problem with outbound http connections from OpenBSD box to external network.
I use as firewall/NAT. The NAT for pc's behind it works ok.

To reproduce problem i use
Code:
ftp http://example.com/index.html
Trying 93.184.216.34...
Requesting http://example.com/index.html
^C
And connection hangs. I attach logs below.

If i use http://93.184.216.34/index.html the download succeeds.

I thought this is related to my pf.conf but I don't see any packet in pflog0 directed to 93.184.216.34.

My external interface is em1 which is used to establish pppoe session with my IP provider.

I captured traffic on pppoe0 and em1 when using DNS or IP address.
I think when using IP address connection ends ok, 93.184.216.34(example.com) sends FIN flag, ther is ACK and FIN from OpenBSD.

When ftp http://example.com/index.html command is used the TCP stream is ended only from example.com side

I have changed my IP in tcpdump to 8.8.8.8.
Also ssh form OpenBSD box to outside machine works well.
I would like to fix it because it blocks syspatch from working, and I ran out of ideas why the connection is closed only from one side when DNS adress is used.


Code:
ftp http://example.com/index.html
tcpdump -s 1500 -Xnnvvvettt -i pppoe0 'host 93.184.216.34'
tcpdump: listening on pppoe0, link-type PPP_ETHER
Jan 15 06:33:56.585752 PPPoE
        code Session, version 1, type 1, id 0x3679, length 66
        IP 8.8.8.8.12281 > 93.184.216.34.80: S [tcp sum ok] 2996088536:2996088536(0) win 16384 <mss 1452,nop,nop,sackOK,nop,wscale 6,nop,nop,timestamp 2780311879 0> (DF) (ttl 64, id 6227, len 64)
  0000: 1100 3679 0042 0021 4500 0040 1853 4000  ..6y.B.!E..@.S@.
  0010: 4006 db3a 0808 0808 5db8 d822 2ff9 0050  @..:..W.].."/..P
  0020: b294 aed8 0000 0000 b002 4000 4622 0000  ..........@.F"..
  0030: 0204 05ac 0101 0402 0103 0306 0101 080a  ................
  0040: a5b8 3147 0000 0000                      ..1G....

Jan 15 06:33:56.709524 PPPoE
        code Session, version 1, type 1, id 0x3679, length 62
        IP 93.184.216.34.80 > 8.8.8.8.12281: S [tcp sum ok] 2428984108:2428984108(0) ack 2996088537 win 65535 <mss 1460,sackOK,timestamp 390670526 2780311879,nop,wscale 9> (ttl 53, id 655, len 60)
  0000: 1100 3679 003e 0021 4500 003c 028f 0000  ..6y.>.!E..<....
  0010: 3506 3c03 5db8 d822 0808 0808 0050 2ff9  5.<.].."..W..P/.
  0020: 90c7 5b2c b294 aed9 a012 ffff 6c11 0000  ..[,........l...
  0030: 0204 05b4 0402 080a 1749 28be a5b8 3147  .........I(...1G
  0040: 0103 0309                                ....

Jan 15 06:33:56.709599 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 8.8.8.8.12281 > 93.184.216.34.80: . [tcp sum ok] 1:1(0) ack 1 win 256 <nop,nop,timestamp 2780311879 390670526> (DF) (ttl 64, id 1689, len 52)
  0000: 1100 3679 0036 0021 4500 0034 0699 4000  ..6y.6.!E..4..@.
  0010: 4006 ed00 0808 0808 5db8 d822 2ff9 0050  @.....W.].."/..P
  0020: b294 aed9 90c7 5b2d 8010 0100 99df 0000  ......[-........
  0030: 0101 080a a5b8 3147 1749 28be            ......1G.I(.

Jan 15 06:33:56.710079 PPPoE
        code Session, version 1, type 1, id 0x3679, length 126
        IP 8.8.8.8.12281 > 93.184.216.34.80: P [tcp sum ok] 1:73(72) ack 1 win 256 <nop,nop,timestamp 2780311879 390670526> (DF) (ttl 64, id 38766, len 124)
  0000: 1100 3679 007e 0021 4500 007c 976e 4000  ..6y.~.!E..|.n@.
  0010: 4006 5be3 0808 0808 5db8 d822 2ff9 0050  @.[...W.].."/..P
  0020: b294 aed9 90c7 5b2d 8018 0100 75be 0000  ......[-....u...
  0030: 0101 080a a5b8 3147 1749 28be 4745 5420  ......1G.I(.GET
  0040: 2f69 6e64 6578 2e68 746d 6c20 4854 5450  /index.html HTTP
  0050: 2f31 2e30 0d0a 486f 7374 3a20 6578 616d  /1.0..Host: exam
  0060: 706c 652e 636f 6d0d 0a55 7365 722d 4167  ple.com..User-Ag
  0070: 656e 743a 204f 7065 6e42 5344 2066 7470  ent: OpenBSD ftp
  0080: 0d0a 0d0a                                ....

Jan 15 06:33:56.833794 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 93.184.216.34.80 > 8.8.8.8.12281: . [tcp sum ok] 1:1(0) ack 73 win 283 <nop,nop,timestamp 390670651 2780311879> (ttl 53, id 678, len 52)
  0000: 1100 3679 0036 0021 4500 0034 02a6 0000  ..6y.6.!E..4....
  0010: 3506 3bf4 5db8 d822 0808 0808 0050 2ff9  5.;.].."..W..P/.
  0020: 90c7 5b2d b294 af21 8010 011b 98ff 0000  ..[-...!........
  0030: 0101 080a 1749 293b a5b8 3147            .....I);..1G

Jan 15 06:33:56.834198 PPPoE
        code Session, version 1, type 1, id 0x3679, length 233
        IP 93.184.216.34.80 > 8.8.8.8.12281: P [tcp sum ok] 1441:1620(179) ack 73 win 283 <nop,nop,timestamp 390670651 2780311879> (ttl 53, id 680, len 231)
  0000: 1100 3679 00e9 0021 4500 00e7 02a8 0000  ..6y...!E.......
  0010: 3506 3b3f 5db8 d822 0808 0808 0050 2ff9  5.;?].."..W..P/.
  0020: 90c7 60cd b294 af21 8018 011b 1650 0000  ..`....!.....P..
  0030: 0101 080a 1749 293b a5b8 3147 696e 2069  .....I);..1Gin i
  0040: 6e20 6c69 7465 7261 7475 7265 2077 6974  n literature wit
  0050: 686f 7574 2070 7269 6f72 2063 6f6f 7264  hout prior coord
  0060: 696e 6174 696f 6e20 6f72 2061 736b 696e  ination or askin
  0070: 6720 666f 7220 7065 726d 6973 7369 6f6e  g for permission
  0080: 2e3c 2f70 3e0a 2020 2020 3c70 3e3c 6120  .</p>.    <p><a
  0090: 6872 6566 3d22 6874 7470 733a 2f2f 7777  href="https://ww
  00a0: 772e 6961 6e61 2e6f 7267 2f64 6f6d 6169  w.iana.org/domai
  00b0: 6e73 2f65 7861 6d70 6c65 223e 4d6f 7265  ns/example">More
  00c0: 2069 6e66 6f72 6d61 7469 6f6e 2e2e 2e3c   information...<
  00d0: 2f61 3e3c 2f70 3e0a 3c2f 6469 763e 0a3c  /a></p>.</div>.<
  00e0: 2f62 6f64 793e 0a3c 2f68 746d 6c3e 0a    /body>.</html>.

Jan 15 06:33:56.834207 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 93.184.216.34.80 > 8.8.8.8.12281: F [tcp sum ok] 1620:1620(0) ack 73 win 283 <nop,nop,timestamp 390670651 2780311879> (ttl 53, id 681, len 52)
  0000: 1100 3679 0036 0021 4500 0034 02a9 0000  ..6y.6.!E..4....
  0010: 3506 3bf1 5db8 d822 0808 0808 0050 2ff9  5.;.].."..W..P/.
  0020: 90c7 6180 b294 af21 8011 011b 92ab 0000  ..a....!........
  0030: 0101 080a 1749 293b a5b8 3147            .....I);..1G

Jan 15 06:33:56.834283 PPPoE
        code Session, version 1, type 1, id 0x3679, length 66
        IP 8.8.8.8.12281 > 93.184.216.34.80: . [tcp sum ok] 73:73(0) ack 1 win 256 <nop,nop,timestamp 2780311880 390670651,nop,nop,sack 1 {1441:1620} > (DF) (ttl 64, id 42781, len 64)
  0000: 1100 3679 0042 0021 4500 0040 a71d 4000  ..6y.B.!E..@..@.
  0010: 4006 4c70 0808 0808 5db8 d822 2ff9 0050  @.Lp..W.].."/..P
  0020: b294 af21 90c7 5b2d b010 0100 7f25 0000  ...!..[-.....%..
  0030: 0101 080a a5b8 3148 1749 293b 0101 050a  ......1H.I);....
  0040: 90c7 60cd 90c7 6180                      ..`...a.

Jan 15 06:33:56.834341 PPPoE
        code Session, version 1, type 1, id 0x3679, length 66
        IP 8.8.8.8.12281 > 93.184.216.34.80: . [tcp sum ok] 73:73(0) ack 1 win 256 <nop,nop,timestamp 2780311880 390670651,nop,nop,sack 1 {1441:1620} > (DF) (ttl 64, id 20407, len 64)
  0000: 1100 3679 0042 0021 4500 0040 4fb7 4000  ..6y.B.!E..@O.@.
  0010: 4006 a3d6 0808 0808 5db8 d822 2ff9 0050  @.....W.].."/..P
  0020: b294 af21 90c7 5b2d b010 0100 7f25 0000  ...!..[-.....%..
  0030: 0101 080a a5b8 3148 1749 293b 0101 050a  ......1H.I);....
  0040: 90c7 60cd 90c7 6180                      ..`...a.
Here tranfsers stops
After ctrl-c resuems
Jan 15 06:34:27.975616 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 8.8.8.8.12281 > 93.184.216.34.80: F [tcp sum ok] 73:73(0) ack 1 win 256 <nop,nop,timestamp 2780311942 390670651> (DF) (ttl 64, id 16765, len 52)
  0000: 1100 3679 0036 0021 4500 0034 417d 4000  ..6y.6.!E..4A}@.
  0010: 4006 b21c 0808 0808 5db8 d822 2ff9 0050  @.....W.].."/..P
  0020: b294 af21 90c7 5b2d 8011 0100 98da 0000  ...!..[-........
  0030: 0101 080a a5b8 3186 1749 293b            ......1..I);

Jan 15 06:34:28.099454 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 93.184.216.34.80 > 8.8.8.8.12281: . [tcp sum ok] 1621:1621(0) ack 74 win 283 <nop,nop,timestamp 390701916 2780311942> (ttl 53, id 5081, len 52)
  0000: 1100 3679 0036 0021 4500 0034 13d9 0000  ..6y.6.!E..4....
  0010: 3506 2ac1 5db8 d822 0808 0808 0050 2ff9  5.*.].."..W..P/.
  0020: 90c7 6181 b294 af22 8010 011b 184a 0000  ..a....".....J..
  0030: 0101 080a 1749 a35c a5b8 3186            .....I.\..1.

Code:
ftp http://93.184.216.34/index.html
tcpdump -s 1500 -Xnnvvvettt -i pppoe0 'host 93.184.216.34'
tcpdump: listening on pppoe0, link-type PPP_ETHER
Jan 15 06:37:09.815142 PPPoE
        code Session, version 1, type 1, id 0x3679, length 66
        IP 8.8.8.8.20858 > 93.184.216.34.80: S [tcp sum ok] 2319111801:2319111801(0) win 16384 <mss 1452,nop,nop,sackOK,nop,wscale 6,nop,nop,timestamp 3833200425 0> (DF) (ttl 64, id 3322, len 64)
  0000: 1100 3679 0042 0021 4500 0040 0cfa 4000  ..6y.B.!E..@..@.
  0010: 4006 e693 0808 0808 5db8 d822 517a 0050  @.....W.].."Qz.P
  0020: 8a3a d679 0000 0000 b002 4000 18b6 0000  .:.y......@.....
  0030: 0204 05ac 0101 0402 0103 0306 0101 080a  ................
  0040: e479 ff29 0000 0000                      .y.)....

Jan 15 06:37:09.936341 PPPoE
        code Session, version 1, type 1, id 0x3679, length 62
        IP 93.184.216.34.80 > 8.8.8.8.20858: S [tcp sum ok] 3116914872:3116914872(0) ack 2319111802 win 65535 <mss 1460,sackOK,timestamp 1620630145 3833200425,nop,wscale 9> (ttl 53, id 37894, len 60)
  0000: 1100 3679 003e 0021 4500 003c 9406 0000  ..6y.>.!E..<....
  0010: 3506 aa8b 5db8 d822 0808 0808 0050 517a  5...].."..W..PQz
  0020: b9c8 58b8 8a3a d67a a012 ffff 1d05 0000  ..X..:.z........
  0030: 0204 05b4 0402 080a 6098 da81 e479 ff29  ........`....y.)
  0040: 0103 0309                                ....

Jan 15 06:37:09.936420 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 8.8.8.8.20858 > 93.184.216.34.80: . [tcp sum ok] 1:1(0) ack 1 win 256 <nop,nop,timestamp 3833200426 1620630145> (DF) (ttl 64, id 14430, len 52)
  0000: 1100 3679 0036 0021 4500 0034 385e 4000  ..6y.6.!E..48^@.
  0010: 4006 bb3b 0808 0808 5db8 d822 517a 0050  @..;..W.].."Qz.P
  0020: 8a3a d67a b9c8 58b9 8010 0100 4ad2 0000  .:.z..X.....J...
  0030: 0101 080a e479 ff2a 6098 da81            .....y.*`...

Jan 15 06:37:09.936946 PPPoE
        code Session, version 1, type 1, id 0x3679, length 128
        IP 8.8.8.8.20858 > 93.184.216.34.80: P [tcp sum ok] 1:75(74) ack 1 win 256 <nop,nop,timestamp 3833200426 1620630145> (DF) (ttl 64, id 7070, len 126)
  0000: 1100 3679 0080 0021 4500 007e 1b9e 4000  ..6y...!E..~..@.
  0010: 4006 d7b1 0808 0808 5db8 d822 517a 0050  @.....W.].."Qz.P
  0020: 8a3a d67a b9c8 58b9 8018 0100 326b 0000  .:.z..X.....2k..
  0030: 0101 080a e479 ff2a 6098 da81 4745 5420  .....y.*`...GET
  0040: 2f69 6e64 6578 2e68 746d 6c20 4854 5450  /index.html HTTP
  0050: 2f31 2e30 0d0a 486f 7374 3a20 3933 2e31  /1.0..Host: 93.1
  0060: 3834 2e32 3136 2e33 340d 0a55 7365 722d  84.216.34..User-
  0070: 4167 656e 743a 204f 7065 6e42 5344 2066  Agent: OpenBSD f
  0080: 7470 0d0a 0d0a                           tp....

Jan 15 06:37:10.057959 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 93.184.216.34.80 > 8.8.8.8.20858: . [tcp sum ok] 1:1(0) ack 75 win 283 <nop,nop,timestamp 1620630266 3833200426> (ttl 53, id 37922, len 52)
  0000: 1100 3679 0036 0021 4500 0034 9422 0000  ..6y.6.!E..4."..
  0010: 3506 aa77 5db8 d822 0808 0808 0050 517a  5..w].."..W..PQz
  0020: b9c8 58b9 8a3a d6c4 8010 011b 49f4 0000  ..X..:......I...
  0030: 0101 080a 6098 dafa e479 ff2a            ....`....y.*

Jan 15 06:37:10.058393 PPPoE
        code Session, version 1, type 1, id 0x3679, length 360
        IP 93.184.216.34.80 > 8.8.8.8.20858: P [tcp sum ok] 1:307(306) ack 75 win 283 <nop,nop,timestamp 1620630267 3833200426> (ttl 53, id 37923, len 358)
  0000: 1100 3679 0168 0021 4500 0166 9423 0000  ..6y.h.!E..f.#..
  0010: 3506 a944 5db8 d822 0808 0808 0050 517a  5..D].."..W..PQz
  0020: b9c8 58b9 8a3a d6c4 8018 011b 5a79 0000  ..X..:......Zy..
  0030: 0101 080a 6098 dafb e479 ff2a 4854 5450  ....`....y.*HTTP
  0040: 2f31 2e30 2032 3030 204f 4b0d 0a41 6363  /1.0 200 OK..Acc
  0050: 6570 742d 5261 6e67 6573 3a20 6279 7465  ept-Ranges: byte
  0060: 730d 0a43 6f6e 7465 6e74 2d54 7970 653a  s..Content-Type:
  0070: 2074 6578 742f 6874 6d6c 0d0a 4461 7465   text/html..Date
  0080: 3a20 5765 642c 2031 3520 4a61 6e20 3230  : Wed, 15 Jan 20
  0090: 3230 2030 353a 3337 3a30 3920 474d 540d  20 05:37:09 GMT.
  00a0: 0a4c 6173 742d 4d6f 6469 6669 6564 3a20  .Last-Modified:
  00b0: 5765 642c 2031 3520 4a61 6e20 3230 3230  Wed, 15 Jan 2020
  00c0: 2030 353a 3337 3a30 3120 474d 540d 0a53   05:37:01 GMT..S
  00d0: 6572 7665 723a 2045 4353 2028 6463 622f  erver: ECS (dcb/
  00e0: 3746 3833 290d 0a43 6f6e 7465 6e74 2d4c  7F83)..Content-L
  00f0: 656e 6774 683a 2039 340d 0a43 6f6e 6e65  ength: 94..Conne
  0100: 6374 696f 6e3a 2063 6c6f 7365 0d0a 0d0a  ction: close....
  0110: 3c68 746d 6c3e 3c68 6561 643e 3c74 6974  <html><head><tit
  0120: 6c65 3e65 6467 6563 6173 7463 646e 2e6e  le>edgecastcdn.n
  0130: 6574 3c2f 7469 746c 653e 3c2f 6865 6164  et</title></head
  0140: 3e3c 626f 6479 3e3c 6831 3e65 6467 6563  ><body><h1>edgec
  0150: 6173 7463 646e 2e6e 6574 3c2f 6831 3e3c  astcdn.net</h1><
  0160: 2f62 6f64 793e 3c2f 6874 6d6c 3e0a       /body></html>.

Jan 15 06:37:10.058403 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 93.184.216.34.80 > 8.8.8.8.20858: F [tcp sum ok] 307:307(0) ack 75 win 283 <nop,nop,timestamp 1620630267 3833200426> (ttl 53, id 37924, len 52)
  0000: 1100 3679 0036 0021 4500 0034 9424 0000  ..6y.6.!E..4.$..
  0010: 3506 aa75 5db8 d822 0808 0808 0050 517a  5..u].."..W..PQz
  0020: b9c8 59eb 8a3a d6c4 8011 011b 48c0 0000  ..Y..:......H...
  0030: 0101 080a 6098 dafb e479 ff2a            ....`....y.*

Jan 15 06:37:10.058448 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 8.8.8.8.20858 > 93.184.216.34.80: . [tcp sum ok] 75:75(0) ack 308 win 251 <nop,nop,timestamp 3833200426 1620630267> (DF) (ttl 64, id 18852, len 52)
  0000: 1100 3679 0036 0021 4500 0034 49a4 4000  ..6y.6.!E..4I.@.
  0010: 4006 a9f5 0808 0808 5db8 d822 517a 0050  @.....W.].."Qz.P
  0020: 8a3a d6c4 b9c8 59ec 8010 00fb 48e0 0000  .:....Y.....H...
  0030: 0101 080a e479 ff2a 6098 dafb            .....y.*`...

Jan 15 06:37:10.069174 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 8.8.8.8.20858 > 93.184.216.34.80: F [tcp sum ok] 75:75(0) ack 308 win 256 <nop,nop,timestamp 3833200426 1620630267> (DF) (ttl 64, id 5600, len 52)
  0000: 1100 3679 0036 0021 4500 0034 15e0 4000  ..6y.6.!E..4..@.
  0010: 4006 ddb9 0808 0808 5db8 d822 517a 0050  @.....W.].."Qz.P
  0020: 8a3a d6c4 b9c8 59ec 8011 0100 48da 0000  .:....Y.....H...
  0030: 0101 080a e479 ff2a 6098 dafb            .....y.*`...

Jan 15 06:37:10.190118 PPPoE
        code Session, version 1, type 1, id 0x3679, length 54
        IP 93.184.216.34.80 > 8.8.8.8.20858: . [tcp sum ok] 308:308(0) ack 76 win 283 <nop,nop,timestamp 1620630399 3833200426> (ttl 53, id 37946, len 52)
  0000: 1100 3679 0036 0021 4500 0034 943a 0000  ..6y.6.!E..4.:..
  0010: 3506 aa5f 5db8 d822 0808 0808 0050 517a  5.._].."..W..PQz
  0020: b9c8 59ec 8a3a d6c5 8010 011b 483b 0000  ..Y..:......H;..
  0030: 0101 080a 6098 db7f e479 ff2a            ....`....y.*
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Old 19th January 2020
J65nko J65nko is offline
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I never used PPPoE and from the logs provided I don't see what is could be wrong. At a first glance ( I have to cook ;-) )

But a common issue with PPPoE is the overhead from 8 bytes added to the standard 1500 ethernet packet size. See https://en.wikipedia.org/wiki/Point-...ad_on_Ethernet

What is the MTU setting of your NIC? You could try setting it to 1492.
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Old 20th January 2020
J65nko J65nko is offline
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I don't think it has anything to do with your setup. When I use firefox on FreeBSD 12.0 I get similar results:
Code:
On firefox address bar: http://93.184.216.34/index.html
Result: edgecastcdn.net

On firefox address bar: http://example.com/index.html
Result: 
Example Domain

This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission.

More information...

=====================

On firefox address bar: http://93.184.216.34/index.html
Result: edgecastcdn.net
I think it is the way the webserver at 93.184.216.34 has been configured.
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Old 20th January 2020
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IdOp IdOp is offline
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Quote:
Originally Posted by J64nko
I think it is the way the webserver at 93.184.216.34 has been configured.
I think this could depend on the value specified in the Host: field of the HTTP GET header. If I add a field saying "Host: example.com" to that header in a request for http://93.184.216.34/index.html then it returns the "Example Domain ..." index.html file. So firefox is likely adding a Host: field to the header (set = to the host specified in the URL) and the webserver is reading it and sending a reply that depends on it.

Last edited by IdOp; 20th January 2020 at 07:15 AM.
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Old 20th January 2020
k2k k2k is offline
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Join Date: Jan 2020
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Quote:
Originally Posted by J65nko View Post
I never used PPPoE and from the logs provided I don't see what is could be wrong. At a first glance ( I have to cook ;-) )

But a common issue with PPPoE is the overhead from 8 bytes added to the standard 1500 ethernet packet size. See https://en.wikipedia.org/wiki/Point-...ad_on_Ethernet

What is the MTU setting of your NIC? You could try setting it to 1492.
Thanks that was it.
I had
Code:
 match in all scrub (reassemble tcp no-df random-id max-mss 1440)
And this worked to my linux box behind the nat as packet was IN and scrubbed to 1440 size.

After adding
Code:
match out all scrub (reassemble tcp no-df random-id max-mss 1440)
FTP connection went trough blazing fast.
I suspected that the FIN packet from OpenBSD box went missing but as there were a lot of traffic there I had trouble looking at the ifconfig statistics.

Thanks again.
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