marcus83
DD-WRT User
Joined: 04 Jan 2024
Posts: 229
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 Posted: Wed Feb 21, 2024 14:30 Post subject: [SOLVED]OpenVPN Log - N write UDPv4 [EMSGSIZE Path-MTU=1500] |
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hi,
I noticed this on the VPN log, I tried all the settings retrieved online, but nothing, I wanted to know is this a problem or can it be ignored?
N write UDPv4 [EMSGSIZE Path-MTU=1500]: Message too large (fd=5 code=90)
Last edited by marcus83 on Thu Feb 22, 2024 3:55; edited 1 time in total |
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marcus83
DD-WRT User
Joined: 04 Jan 2024
Posts: 229
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| Posted: Wed Feb 21, 2024 16:48 Post subject: |
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| kernel-panic69 wrote: | | If your MTU is set to 1500 for OpenVPN, then you didn't read the documentation thoroughly. |
yes I set it to the OpenVPN MTU default 1500, everything works fine, except this one I noticed, is it a problem? |
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Alozaros
DD-WRT Guru
Joined: 16 Nov 2015
Posts: 6447
Location: UK, London, just across the river..
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| Posted: Wed Feb 21, 2024 20:23 Post subject: |
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| marcus83 wrote: | | kernel-panic69 wrote: | | If your MTU is set to 1500 for OpenVPN, then you didn't read the documentation thoroughly. |
yes I set it to the OpenVPN MTU default 1500, everything works fine, except this one I noticed, is it a problem? |
KP-69 i guess it is a precedent...inn'it..
| kernel-panic69 wrote: | | If your MTU is set to 1500 for OpenVPN, then you didn't read the documentation thoroughly. |
| marcus83 wrote: | | yes I set it to the OpenVPN MTU default 1500, everything works fine, except this one I noticed, is it a problem? |
you clearly didn't read the OpenVPN documentation...as somewhere there its mentioned, that the default tunnel MTU is set to 1400 and even better use less 1392 and so...you dont read, but set it as default 1500... 
And this is wrong..
_________________
Atheros
TP-Link WR740Nv1 ---DD-WRT 55630 WAP
TP-Link WR1043NDv2 -DD-WRT 55723 Gateway/DoT,Forced DNS,Ad-Block,Firewall,x4VLAN,VPN
TP-Link WR1043NDv2 -Gargoyle OS 1.15.x AP,DNS,QoS,Quotas
Qualcomm-Atheros
Netgear XR500 --DD-WRT 55779 Gateway/DoH,Forced DNS,AP Isolation,4VLAN,Ad-Block,Firewall,Vanilla
Netgear R7800 --DD-WRT 55819 Gateway/DoT,AD-Block,Forced DNS,AP&Net Isolation,x3VLAN,Firewall,Vanilla
Netgear R9000 --DD-WRT 55779 Gateway/DoT,AD-Block,AP Isolation,Firewall,Forced DNS,x2VLAN,Vanilla
Broadcom
Netgear R7000 --DD-WRT 55460 Gateway/SmartDNS/DoH,AD-Block,Firewall,Forced DNS,x3VLAN,VPN
NOT USING 5Ghz ANYWHERE
------------------------------------------------------
Stubby DNS over TLS I DNSCrypt v2 by mac913 |
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marcus83
DD-WRT User
Joined: 04 Jan 2024
Posts: 229
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| Posted: Thu Feb 22, 2024 3:54 Post subject: |
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I was finally able to calculate the correct MTU of my connection.
1) Identifying correct MTU:
On Windows
ping -n 1 -l 1500 -f www.example.com
On Linux
ping -M do -s 1500 -c 1 www.example.com
On OSX
ping -D -v -s 1500 -c 1 www.example.com
Decrease the 1500 value by 10 each time, until the ping succeeds. Once the ping succeeds, the value used is the MTU you should use.
2) OpenVPN requires a value called the MSS to be set. The MSS is the value for the MTU minus 40)
Eg. If your MTU is 1460, your MSS is 1420
MSS = MTU - 40
MSS = 1460 - 40
MSS = 1420
then add the following value to the additional configuration:
mssfix 1420
DONE! |
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