Questions tagged [mtu]

"Maximum Transmission Unit" (MTU) is the maximum number of bytes a frame or packet may have on a network (in several layers of the OSI model). Wrong MTU can lead to packet loss.

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OpenConnect force clients to use special cipher

I use ocserv on Centos as Openconnect VPN and I use config file for setting up the server I need to force clients to use special cipher like AES-256-GCM because it seems that VPN blocks on some 4G net ...
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Jumbo MTU and switches

I have a network with several file servers, workstations and application servers. For simplicity we can consider it all attached to a single switch, say Dell 4032F with maximum Jumbo MTU size of 9216. ...
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"very high" (probably?) MTU being set automatically on wireguard interface

So, I have a VPS running on Amazon Lightsail and I installed wireguard on it; I setup an interface this way: [Interface] Address = 10.255.128.1/24 MTU = 1420 SaveConfig = true PostUp = iptables -A ...
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forwarded TCP traffic is refragmented on Linux despite the "Don't fragment" flag

We have 2 VPN servers at the same hoster. The servers are virtual and they have different Linux distros. The VPN clients establish https connections to the same Amazon EC2 server. The TCP packets from ...
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PMTUD/ICMP black hole problems across a VXLAN tunnel

I'm running a Proxmox PVE host and am trying to use VXLAN to connect the machines running on it to various networks in our Lab. However, I'm running into weird MTU-related problems that I don't ...
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Tplink router on wisp mode with zte 4g lte modem

Which is better for 8 users doing voip , watching youtube videos, browsing and playing multiplayer online games at a time ? Beacon interval 100/dtim interval 1 B.i. 200 / dtim 1 B.i. 50/dtim 4 B.i. 50/...
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Increasing MTU size

Why would increasing the VLAN MTU size cause things to break? We have a customer who wants 2000 byte packets for some reason, so I increased all the physical links to 9216, which didn't cause any ...
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Windows MTU can no longer be set higher than 1500 Bytes?

For some time we have been using jumbo frames on several computers without problems. But suddenly I am no longer able to increase the MTU on some computers to more than 1500 Bytes. netsh returns error ...
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ssh through openVPN on openWRT hangs on SSH2_MSG_KEXINIT sent

I'm encountering a problem where ssh to a remote server hangs with the message SSH2_MSG_KEXINIT sent. I have already explored the MTU options with no luck. Case 1 (fails) This happens when I ssh from ...
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How to setup permanent MTU size in RHEL 7 for eth0 interface?

I am using RHEL 7 and trying to setup permanent MTU size to 8500. Not able to find a way to set it up permanently. The server does not have dhcp.conf file in it. I am using below command for temporary ...
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Why would MTU be a size of 96? [closed]

So after discovering I can increase internet speed by tweaking the MTU, it appears I have a MTU of only 96 bytes. Any idea why that is? ping -c 3 -M do -s 68 google.com PING google.com (172.217.169.46)...
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NFS insists to send packets over MTU, nftables might be the solution

I have an NFS mount over a Strongswan IPSec tunnel, which is encapsulated in a 6to4 tunnel. The IPSec is because I need encryption for NFS traffic, the 6to4 is because the VPS provider won't assign a ...
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Cannot transfer data from one specific system (MTU issue?)

Summary The default MTU value prevents data transfer for one system. Reducing it manually enables the data transfer once more, but this manual adjustment is unnecessary on an adjacent system. ...
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Setting the MTU of a virtual Switch on a qNAP NAS (QTSHero OS)

For a project that I am currently working for, I bought a QNAP NAS (TVS-h1288X). In that project, I have multiple network cameras. On the NAS, I have a Windows 10 VM which is supposed to store all the ...
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Different length between ping and tcpdump

I do not why I am not able to see under tcpdump the correct length value which should be $((9706-28)) = 9678, but I see 9686. On both side there is a MTU set to 9706 which maximum value for the ...
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Requirements to achieve Jumbo Frame (mtu = 9000) with PXE Enabled networks

What I should be looking for when trying to enable Jumbo Frames in networks that relies on PXE for server booting? As far as I know I must have: Network switch capable of MTU >= 9000 The ability ...
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Can't reach server probably caused by openvpn mtu

What I try to achieve: Reach the server on LAN via OpenVPN Symptoms: SSH connection hangs on SSH2_MSG_KEXINIT ssh -vvv emmy@10.0.0.101 OpenSSH_8.2p1 Ubuntu-4ubuntu0.2, OpenSSL 1.1.1f 31 Mar 2020 ...
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How to change cisco 3750 specific port MTU to 9000?

How to change cisco 3750 specific port MTU to 9000? I do not want to set it as a system global command for all ports.
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Why does setting MTU 1452 solve Internet problems and how to fix root cause?

In our church we get Internet uplink from a friendly neighbor’s WiFi. At first everything seemed (at least) fine but since some weeks general “Internet stability problems” increased and since approx. ...
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SSH pauses - perhaps MTU/packet size too large - how to confirm and possibly resolve?

I have a MacOS client and Linux server (non-root access). I'm using 2 versions of a tool for remote desktop control. Version 2 worked pretty well - some small bugs. The vendor has updated to version 3....
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Does changing MTU need restarting the application?

Let us say we have an aerospike cluster running with interface mtu as 1500. If I want to switch to jumbo frames, do I need to restart the aerospike cluster? If yes, why?
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hetzner private network, 1 docker host, 1 pfsense, I keep getting "TCP Previous segment not captured" from my containers

this is the network design https://imagebin.ca/v/5NNDpuDwq9PT it's hosted on hetzner, 1 firewall with a public facing interface, pfsense. 1 docker host with two interfaces, one connected to the ...
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SSH connection problems through OpenVPN tunnel (“TCP Previous segment lost”)

I have a VPN tunnel to an OpenVPN server. The VPN is a Sophos VPN which uses OpenVPN under the hood. I do not know the server configuration nor can I change the server config. My tunnel endpoint is ...
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MTU 9000 and 1500 when machines with MTU 1500 send data to machines with MTU 9000

we have some machines in the cluster linux machines as Linux_a , linux_b are configured with MTU 1500 while linux machines - linux_1 and linux_2 are configured with MTU 9000 so linux machines - ...
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how to safely increase a network's MTU

I want to increase the Ethernet Maximum Transmission Unit (MTU) for some hosts on a local network. Is there a known sequence of steps to follow? Or, can I just tweak each host's MTU as needed and it ...
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Path MTU is not always 9000, only in one direction

I have a question about MTU or path MTU. In my setup I have 2 computers (firewall, Windows PC) and one NAS, each with a gigabit interface. They are connected throughout the same gigabit switch. In all ...
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How is the Ethernet payload only max 1500, while I can ping with larger size packet?

Just recently I came to know that the payload of Ethernet is max 1500 bytes (mtu). The first thing that came to my mind was that we can ping with much more size than that. So I thought maybe the ...
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Ping : How to differentiate between Host powered off and MTU too long?

I changed the eth0 MTU size to 1550(using : ifconfig eth0 mtu 1550) and ran ping -c 1 -M do -s 1500 -w 5 {some other IP} and The output I see is, --- x.x.x.x ping statistics --- 5 packets ...
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I can not decrease MTU on my nic

I'm trying to decrease the MTU value on my machine but I receive this response: [root@apache1bpreprod acn]# ifconfig eth0 mtu 1350 SIOCSIFMTU: Invalid argument Why? i expect problems to increase not ...
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can we mix MTU values in cluster

we have hadoop cluster ( all machines are linux redhat machines version 7.x ) on the VM machines we set MTU=8900 and all other machines we set MTU=9000 we set on VM MTU=8900 because we saw some ...
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Running a Dual Stack OpenVPN server: IPv6 sorta works - however, large packets appear to fail

I'm running a Dual Stack OpenVPN Server, setup according to this tutorial: https://techblog.synagila.com/2016/02/24/build-a-openvpn-server-on-ubuntu-to-provide-a-ipv6-tunnel-over-ipv4/ . As shown in ...
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Force jumbo packet fragmentation

We are in a cluster environment. We have compute nodes with jumbo packets enabled and a MTU of 9000. We are running into some issues in tracebacks to an address outside of our lan, where jumbo packets ...
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Problems with TCP retransmission, duplicates etc. on CentOS Linux

I'm running Vyattagateway with a CentOS Linux behind, and IPSec tunnel in front. Trying to display my setup: PARTNER-NETWORK <--- IPSec (GRE, MTU 1420) ---> VYATTA (TUNNEL, MTU 1420 <> ...
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dose setting Jumbo frame on linux redhat influencing OS performance?

We set the MTU to 9000 on all our linux machines ( we have redhat machines version - 7.3 ) , linux machines are part of hadoop clusters we want to know if set the MTU to 9000 can be negative on OS ...
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how to know if my servers should use huge pages ( memory page size )

we have several servers in cluster , and we want to know what in general in which cases we need to configure huge pages ? I have also few quastions dose "memory page size" is equal to Huge pages ? ...
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linux fine tuning after setting the MTU to jumbo frame

We want to set the MTU to 9000 bytes on our Linux machines (distribution is Redhat 7) In this case, how would I tune the memory page size according to MTU size of 9000 bytes? Also, what are the ...
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MTU issue - Packet loss with certain Destination

A customer is having issue with our system and after investigating and analyzing tcp traffic with tcpdump, I noticed that fragmented packets were not received by our cloud server (OVH). I did some ...
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Random connection resets between browser and Linux server - MTU wrong or ICMP not getting through?

I've been seeing random ERR_CONNECTION_RESET errors in my browser (Chrome, Firefox or Edge running on different machines, Windows 10 1709) when I try to edit web pages on a remote Linux server running ...
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Slower performance using Jumbo Frames on Dell PowerVault MD3200i

We have a Dell PowerVault MD3200i connected to a server via iSCSI using 2 Dell switches (PowerConnect 6224) at 1GB. The server has VMware ESXi 6.5 installed and it's connected to the PowerVault using ...
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Centos 7 pptpd mtu size

i'm using pptpd on centos7 as PPTP VPN Server how can I change the MTU size on server side cause some users cannot connect to the server thanks
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ping fails with MTU >= 298

For context, my original problem is that my ssh connection to my servers hangs at expecting SSH2_MSG_KEX_ECDH_REPLY when i connect to them via VPN (in this case, an OpenVPN running in pfsense). The ...
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VirtualBox adapter MTU settings over 1500

I create an adapter for Oracle VirtualBox (as a host-only). It runs perfectly; but I need to change MTU size to 1600. When I come back to host-PC and I opened terminal. Then I got these results. ...
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Cisco 2960X and Jumbo frames on particular ports

I would like to setup several ports to be able handle jumbo frames. This will be only for my backup nas connected to ESXi host. I did create vlan 103 where I changed mtu size to 9000. Problem is when ...
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Reassembly fails at destination

Say I have Host1 & 2 connected to a router with different speeds. Host1 <--100 Mbps--> Router <--10 Mbps--> Host2 Host1 sends 10MB of UDP data using nc command to Host2, but the ...
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Can't ping remote host through nat on ipsec enc0 (mtu=0)

I'm up ipsec vpn to remote host. Since the remote host accepts only one ip i'm up nat for local net on enc0. Ping from ipsec host is ok: PING 172.20.162.150 (172.20.162.150): 56 data bytes 64 bytes ...
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Is there a utility or way to get the PMTU/MTU of a remote system quickly?

Is there a utility or linux built in to get the PMTU/MTU of a remote system quickly (sub 1 second preferably)? If so what is it and what syntax does it require? Google searches have not been my ...
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Chained network issue/ MTU size

I have a chain of devices connected to the Internet: Draytek 2120n-plus Fibre router in a Metal Shed - Internet connection TP-Link AV500 Powerline Adapter Draytek 2760 VDSL Router, used as Wireless ...
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Jumbo frames (mtu 9000) on Debian 7.10 servers with BCM57800 NIC (bnx2x)

I'm working on 2 servers under Debian 7.10 with Broadcom Corporation NetXtreme BCM57800 1/10 Gigabit ethernet. I have done the following for both servers: ethtool -g eth0 Ring parameters for eth0:...
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HTTP webserver gateway timeout 504 only from one ISP

I have configured a nginx http webserver to serve a site on CentOS 6 Virtual machine. every things are works fine but when I connect to site from a special ISP, the site wait and after a while respond ...
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VLANs with mixed MTUs trunked over a LAG

I'm contemplating enabling Jumbo frames for a specific network/VLAN (a dedicated storage network). Ports are spread across two switches, linked together using a LAG, which is configured to carry all ...
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