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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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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Windows PMTU black hole detection works for some connections by not others

It seems a part of the network doesn't allow Ethernet frames larger than 1510 bytes (excluding checksum), making the allowed MTU be 1496 bytes instead of the standard 1500 bytes and thus frames that ...
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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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Sent type 3 code 4 with scapy won't update MTU

I have this configuration: H1<-->R1<-->H2 Beetween H1 & R1: Mtu set at 800 Beetween H2 & R1: Mtu set at 1500 Sending an ICMP too big from R1, generate an ICMP ERROR of Type 3 ...
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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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Reset MTU with forged ICMP Type 3, Code 4 packet

I have four Virtual machines in this configuration configuration Router A and Router B are communicating each other beetween an IPsec implementation. So beetween them there is a tunnel up, and when A ...
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PPTP VPN Issue (cross-continent)

I have configured a VPN server in North America. I can connect to it if I connect from the same region (from a different ISP). If I try to connect to it from a faraway place, it fails. It fails after ...
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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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1k 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 ...
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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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4k 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 ? ...
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502 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 ...
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278 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 ...
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242 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 ...
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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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454 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
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723 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 ...
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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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2k 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 ...
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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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705 views

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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789 views

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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285 views

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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2k views

How to setup linux to retransmit TCP packets by reducing the packet size like OS X

On OS X I noticed that for packets which are not ACKed, the system retransmits them with reduced packet size. This can be seen in the image below. Is it possible to enable the same behavior in Linux ...
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Linux host does not retransmit with a lower packet size in response to ICMPv6 Packet Too Big message

I'm seeing this in Wireshark when curling this URL: On the same network, a Windows host retransmits properly, but an Android host does not. On a different network (presumably appropriately configured)...
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Can I trust a TCP segment with a payload of 255 bytes will be delivered in a single Ethernet frame?

I'm writing some server software that upgrades the firmware on an electronic device. It's a tricky task, because currently these devices don't have enough memory to hold a full firmware before ...
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Packetloss over Internet for "Linux-Linux" but not for "Windows-Linux" (tl;dr: it's MTU)

I am right now getting additional grey hair fighting a phenomenon concerning packet loss between machines on the Internet. Check the diagram below. Note that whenever I use "SSH" I could use "HTTPS"; ...
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OpenVPN low performance. Do I have MTU problems? Dumps inside

I have problems with an OpenVPN tunnel which does not reach line speed. The gateway is a Debian Jessy virtual server hosted at OVH. The client is either my freebsd 10.2 homeserver (Intel I3 Ivy Bridge)...
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17k views

Forcing IP fragmentation and reassembly for some traffic thru a VPN tunnel

Is there a way to force IP packet fragmentation before they go into tun0 and then force reassemble them on the other side of tun device? I have some IPSec traffic that I can not control, and it wants ...
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6k views

Why can I receive ethernet frames bigger than my current MTU size?

I configured the MTU size to 1000 with ip link set eth0 mtu 1000 on link eth0. I disabled Generic receiving offloading (gro) with ethtool -K gro off (since this can lead to "false" frame length in ...
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317 views

Force Windows to send packets as soon as they arrive the nic

I have a network application running on Windows Server 2008 R2, that must send small packets in a very short time interval, each microsecond matters. My problem is that windows accumulates the packets ...
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Server Not Working With Jumbo MTUs

I am a network engineer & my server guy doesn't appear to be able to get the jumbo MTU's to work on his NIC team. We are using LACP for two 10gig interfaces between the switch. I am 100% certain ...