Acked-by: Gert Doering <g...@greenie.muc.de>
Stared-at-code, discussed on IRC, and dropped "Changes.rst" entry, as
user-visible behaviour is no longer changed (no default-MTU change).
Tested on the server testbed, having one instance do "tun-mtu 1400 1500"
now, and depending on client version, have it push MTU or not.
The OCC lying feature works - tried "max-mtu 1400 1490" and got
WARNING: 'tun-mtu' is used inconsistently, local='tun-mtu 1490',
remote='tun-mtu 1500'
.. we need to do something about OCC and link-mtu, though...
WARNING: 'link-mtu' is used inconsistently, local='link-mtu 1442',
remote='link-mtu 1545'
(outside of this patch, but annoying)
Also tested with "--tun-mtu 2000 1500", to trigger the "client cannot
handle this" message... works. Well, sort of - the server still sends
a too-big MTU...
194.97.140.21:50362 peer info: IV_MTU=1800
cron2-freebsd-tc-amd64/194.97.140.21:50362 Warning: reported maximum MTU from
client (1800) is lower than MTU used on the server (2000). Add tun-max-mtu 2000
to client configuration.
cron2-freebsd-tc-amd64/194.97.140.21:50362 SENT CONTROL
[cron2-freebsd-tc-amd64]: 'PUSH_REPLY,... cc-exit tls-ekm,tun-mtu 2000'
(status=1)
.. but the client ignores this...
OPTIONS IMPORT: tun-mtu set to 2000
Server-pushed tun-mtu is too large, please add tun-mtu-max 2000 in the client
configuration
.. and configures 1800 (configured --max-tun-mtu on the client).
tcpdump confirms that pings *inside* the tunnel go up to 1800 without
fragmentation...
13:29:57.041939 IP 10.204.2.6 > 10.204.0.1: ICMP echo request, id 49729, seq
31, length 1780
13:29:57.042693 IP 10.204.0.1 > 10.204.2.6: ICMP echo reply, id 49729, seq 31,
length 1780
.. but if I go larger ("ping -s 2000") the MTU mismatch "server 2000,
client 1800" strikes, and I get
2022-11-14 13:30:13 tun packet too large on write (tried=1996,max=1968)
(--tun-mtu-max 2000 on the client will fix this). This is expected -
there is some headroom, but not "200 bytes". So when going large-mtu,
ensure your client configs are matching.
Your patch has been applied to the master branch.
commit 761575cb7b49e94f361c6aaf4bb43d7c7baa5b38
Author: Arne Schwabe
Date: Wed Nov 9 16:48:10 2022 +0100
Push server mtu to client when supported and support occ mtu
Signed-off-by: Arne Schwabe <a...@rfc2549.org>
Acked-by: Gert Doering <g...@greenie.muc.de>
Message-Id: <20221109154810.1268403-2-a...@rfc2549.org>
URL:
https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25499.html
Signed-off-by: Gert Doering <g...@greenie.muc.de>
--
kind regards,
Gert Doering
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