[Openvpn-users] Traffic slow on VPN

["Julio Maidanik" <juliomaidanik@xxxxxxxxxxx>]

Hi,

I have succesfully established the VPN beween two sites, connected through
ADSL, and now I am going into business, i.e. get some useful work done.
I am running an application which reads/writes (but mostly reads) data on a
remote folder, and it is running unbearably slow.

Below I enclose some sample captured packets, and what I observe is a couple
of "good" packets (i.e. of size 844 bytes) followed by lot of small packets,
which waste a lot of bandwidth.
Furthermore, some of those long packets appear repeated, as if 10.0.0.2 gets
impatient on not receiving an ack.

Basically my question is how to improve performance, and my hypothesis are

a) Doesn't appear to be fragmentation problem, because packets are mostly
very short.
I am using mssfix 1300 to handle this and there are not packets which get
even close to that size.

b) On the other hand, it appears that Windows timeout is very short (about
300msec), and after repeating the not-acknowledged packet, it resumes with
shorter packets, slowly incrementing the size of transmission when
succeeding  (but not the rate).

For example, the following packet
16:32:59.542614 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 17324:18168(844)
ack 6289 win 8394 (DF)

Is resent after 300 msec:
16:32:59.886924 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 17324:18168(844)
ack 6289 win 8394 (DF)

c) The short packets are to kee-alive the session, but do not convey any
useful information.

It might be possible to improve the situation tweaking the time-out
parameters?
The repeated datagrams are originated at OpenVPN or the application layer?

Any suggestions?

Julio
//////////////////////////////////////
Captured packets:
16:32:58.726340 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6112:6171(59) ack
17080 win 63274 (DF)
16:32:58.980964 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 17080:17256(176)
ack 6171 win 8512 (DF)
16:32:58.981753 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6171:6230(59) ack
17256 win 64448 (DF)
16:32:59.186186 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 17256:17324(68) ack
6230 win 8453 (DF)
16:32:59.187485 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6230:6289(59) ack
17324 win 64380 (DF)
16:32:59.542614 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 17324:18168(844)
ack 6289 win 8394 (DF)
16:32:59.544074 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6289:6354(65) ack
18168 win 63536 (DF)
16:32:59.886924 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 17324:18168(844)
ack 6289 win 8394 (DF)
16:32:59.888053 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: . ack 18168 win 63536
(DF)
16:32:59.894531 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 18168:18211(43) ack
6354 win 8329 (DF)
16:32:59.896984 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6354:6419(65) ack
18211 win 63493 (DF)
16:33:00.411775 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 18211:18254(43) ack
6419 win 8264 (DF)
16:33:00.412369 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: . ack 18254 win 63450
(DF)
16:33:00.412761 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6419:6478(59) ack
18254 win 63450 (DF)
16:33:00.686626 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 18254:18430(176)
ack 6478 win 8205 (DF)
16:33:00.687406 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6478:6537(59) ack
18430 win 63274 (DF)
16:33:00.918676 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 18430:18498(68) ack
6537 win 8146 (DF)
16:33:00.919516 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6537:6596(59) ack
18498 win 64448 (DF)
16:33:01.268221 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 18498:19342(844)
ack 6596 win 8087 (DF)
16:33:01.269689 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6596:6661(65) ack
19342 win 63604 (DF)
16:33:01.488196 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 19342:19385(43) ack
6661 win 8022 (DF)
16:33:01.488893 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6661:6726(65) ack
19385 win 63561 (DF)
16:33:01.702132 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 19385:19428(43) ack
6726 win 7957 (DF)
16:33:01.702807 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6726:6785(59) ack
19428 win 63518 (DF)
16:33:01.943781 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 19428:19604(176)
ack 6785 win 7898 (DF)
16:33:01.944539 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6785:6844(59) ack
19604 win 63342 (DF)
16:33:02.256424 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 19604:19672(68) ack
6844 win 7839 (DF)
16:33:02.257073 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6844:6903(59) ack
19672 win 63274 (DF)
16:33:02.631415 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 19672:20516(844)
ack 6903 win 7780 (DF)
16:33:02.632883 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6903:6968(65) ack
20516 win 64448 (DF)
16:33:02.844810 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 20516:20559(43) ack
6968 win 7715 (DF)
16:33:02.845523 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 6968:7033(65) ack
20559 win 64405 (DF)
16:33:03.056933 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 20559:20602(43) ack
7033 win 7650 (DF)
16:33:03.057604 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 7033:7092(59) ack
20602 win 64362 (DF)
16:33:03.290298 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 20602:20778(176)
ack 7092 win 7591 (DF)
16:33:03.291082 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 7092:7151(59) ack
20778 win 64186 (DF)
16:33:03.508773 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 20778:20846(68) ack
7151 win 7532 (DF)
16:33:03.509458 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 7151:7210(59) ack
20846 win 64118 (DF)
16:33:03.875365 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 20846:21690(844)
ack 7210 win 7473 (DF)
16:33:03.876837 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: P 7210:7275(65) ack
21690 win 63274 (DF)
16:33:04.204466 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 20846:21690(844)
ack 7210 win 7473 (DF)
16:33:04.204656 10.0.0.2.netbios-ssn > 10.2.0.1.64748: P 21690:21733(43) ack
7275 win 7408 (DF)
16:33:04.205655 10.2.0.1.64748 > 10.0.0.2.netbios-ssn: . ack 21690 win 63274
(DF)

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