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.

Filter by
Sorted by
Tagged with
0 votes
2 answers
336 views

New network not using updated TLS and failing to connect to certain websites

I have 2 networks that are configured just about identically. The both have the same Router - Mikrotik RB2011UiAS-RM, with a direct fiber link to the ISP. I am using the same ISP for both networks. ...
fatdollar's user avatar
1 vote
1 answer
309 views

Ping with jumbo frames fail but returns default ping fail message

I need to set up a local connection between my Windows 11 PC and an external device (IP 10.0.0.10), with jumbo frames enabled (MTU 9000). The end goal on my PC is to connect to the remote device from ...
C. Crt's user avatar
  • 111
0 votes
0 answers
83 views

Unable to receive TCP packets larger than VPC MTU on Google Compute Engines (Redis Client)

This seems to be network issues between Redis cluster (Deployed on our site's on-prem worker node) and Redis client (On GCP VM that is connected to our site via Cloud VPN). Specifically, the issue is ...
Sung-IL's user avatar
0 votes
0 answers
734 views

MTU resetting back to 1500 after `netplan apply`

I'm trying to change the MTU of the eth0 interface on my machine running Ubuntu 18.04 (Nvidia Jetson Xavier NX). Running sudo netplan apply successfully sets the mtu for eth0 to 1280. Unfortunately, ...
Ben Butterworth's user avatar
1 vote
0 answers
502 views

What's magical about MTU and packet drops?

With default MTU as shown below: hosta$ ifconfig eth0 | grep mtu eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 I can ping from a different server using a 1500 payload hostb$ ping -...
Srikanth's user avatar
0 votes
1 answer
241 views

strongSwan VPN tunnel (IKEv2) established but traffic times out

I have a VPN server that tunnels traffic to a PostgreSQL database server which is otherwise unreachable from the internet. The VPN is only reachable by IPv4. Problem All clients can establish a VPN ...
ffrosch's user avatar
  • 121
1 vote
1 answer
951 views

which Wireguard MTU is chosen when each side has a different MTU value?

tl;dr given a Wireguard client and server with different MTU values, which value is used? Given a Wireguard "client" with configuration file [Interface] MTU = 1440 ... and a Wireguard "...
JamesThomasMoon's user avatar
1 vote
1 answer
519 views

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 ...
Farhad Sakhaei's user avatar
0 votes
1 answer
584 views

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. ...
Dima's user avatar
  • 1
4 votes
1 answer
6k views

"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 ...
Yoel Navas Escalante's user avatar
1 vote
1 answer
781 views

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 ...
basin's user avatar
  • 558
1 vote
0 answers
301 views

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 ...
Christopher Engelhard's user avatar
1 vote
1 answer
878 views

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 ...
abatie's user avatar
  • 93
4 votes
0 answers
6k views

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 ...
Timmy Brolin's user avatar
1 vote
3 answers
8k views

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 ...
Piyush Patil's user avatar
-1 votes
1 answer
2k views

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)...
enkor's user avatar
  • 99
1 vote
0 answers
513 views

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 ...
MegaBrutal's user avatar
0 votes
1 answer
95 views

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. ...
Chris Davies's user avatar
  • 1,716
-1 votes
1 answer
995 views

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 ...
vatbub's user avatar
  • 129
1 vote
1 answer
264 views

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 ...
sqr's user avatar
  • 15
1 vote
2 answers
1k views

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 ...
Vinícius Ferrão's user avatar
2 votes
1 answer
1k views

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 [email protected] OpenSSH_8.2p1 Ubuntu-4ubuntu0.2, OpenSSL 1.1.1f 31 Mar 2020 ...
Benedikt Lang's user avatar
0 votes
1 answer
452 views

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.
hamid's user avatar
  • 43
0 votes
1 answer
5k views

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. ...
Daniel Böhmer's user avatar
1 vote
0 answers
1k views

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....
nachum's user avatar
  • 141
1 vote
2 answers
1k views

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?
Tarun Dev's user avatar
1 vote
1 answer
699 views

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 ...
dada216's user avatar
  • 33
3 votes
1 answer
3k views

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 ...
divB's user avatar
  • 570
1 vote
0 answers
227 views

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 - ...
shalom's user avatar
  • 501
0 votes
1 answer
218 views

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 ...
JamesThomasMoon's user avatar
0 votes
0 answers
107 views

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 ...
Hirsch's user avatar
  • 1
0 votes
1 answer
2k views

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 ...
AhmedWas's user avatar
  • 373
0 votes
1 answer
142 views

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 ...
PleaseHelp's user avatar
-1 votes
2 answers
266 views

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 ...
Peppe Del Prete's user avatar
1 vote
2 answers
110 views

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 ...
shalom's user avatar
  • 501
2 votes
0 answers
2k views

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 ...
Freek's user avatar
  • 521
0 votes
1 answer
279 views

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 ...
Martin Forde's user avatar
1 vote
1 answer
2k views

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 <> ...
Alfred Balle's user avatar
0 votes
1 answer
404 views

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 ...
shalom's user avatar
  • 501
1 vote
2 answers
6k views

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 ? ...
shalom's user avatar
  • 501
0 votes
1 answer
699 views

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 ...
shalom's user avatar
  • 501
0 votes
0 answers
335 views

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 ...
JPelletier's user avatar
1 vote
1 answer
636 views

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 ...
Phil McKerracher's user avatar
4 votes
2 answers
1k views

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 ...
Alberto Medina's user avatar
0 votes
0 answers
545 views

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
Pedram Masoumi's user avatar
1 vote
3 answers
1k views

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 ...
iCart's user avatar
  • 113
1 vote
0 answers
1k views

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. ...
user428688's user avatar
0 votes
1 answer
2k views

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 ...
Roman Bielich's user avatar
0 votes
1 answer
3k views

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 ...
Jeyaram's user avatar
  • 101
2 votes
0 answers
411 views

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 ...
Morry's user avatar
  • 21