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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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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How to set an LXD's veth MTU? (parent is a manual bridge)

Can't figure out how to make the veth devices come up with MTU 9000. This is on Ubuntu 18.04.2 with LXD 3.17. The hardware interface is set to 9000, the bridge is set to 9000, and until the LXD is ...
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ipv6 tunnel connection issues with OpenWRT and macOS

I have IPv6 tunnel from Tunnelbroker and dynamic IP from ISP. Tunnel was (and is) working fine for years, at least since 2015. I run OpenWRT stable 18.06.4 on x86 h/w or TP-Link Archer C7 and macOS ...
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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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yet another issue with MTU 9000 on eth on vlan and macvtap

I was wondering how to configure mtu 9000 on a ethernet interface and a vlan, furthermore on the vlan I have a macvtap. If I configure eth4 for mtu 9000, the mtu of the vlan cannot be 9000 anymore ...
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536 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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518 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 <> ...
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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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436 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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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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613 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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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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548 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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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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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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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 ...
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How to prevent SSH freezes over an openvpn client to client connection

I have the exact same issue as the one described here, but I cannot request clarification from the author, since I am a new user and I cannot post a comment on that, so I am posting a new question (I ...
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Change Xenserver 6.5 MTU

How do I go about change the MTU setting for my management interface in xenserver 6.5? Right now its set to the default 1500 but I want to increase it to 9000. For my setup I have 2 nics on each host ...
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How to set permanent mtu size for ppp0

every time I connect to my VPN, I should run sudo ifconfig ppp0 mtu 1300 How could I make it permanent? I'm using Ubuntu 14.04
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871 views

Linux MTU and UDP

Can someone please explain this behavior to me. I have a few VMS (centos) running on a cloud provider. The interface is set to the standard 1500 MTU pining with large ICMP packets work fine: # ...
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What should happen when receiving an ICMP Fragmentation Needed message?

In general, and in particular on a Solaris 10 machine ... See, we are having an issue in our network. I handle some reverse proxy instances on a Solaris 10 server that is behind a load balancer, and ...
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VPN problems: MTU and Don't-Fragment

I am setting up a VPN on Ubuntu 14.04LTS which uses IPSEC and performs NAT for clients. It is basically working - I can connect to it from a clinet (Android device) and browse (for example) www....
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Does TCP's MSS hide a mismatched intra-LAN MTU?

I'm trying to understand how mismatched MTUs behave in a network. Suppose two hosts are able to talk to each other through an Ethernet-based network. The network and host A are configured for jumbo ...
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Can't SSH to any servers

It's for a day that I can't login through SSH to my servers. Using both Putty and MobaXterm. MobaXterm ends with: debug1: sending SSH2_MSG_KEX_ECDH_INIT debug1: expecting SSH2_MSG_KEX_ECDH_REPLY Read ...
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Fragmented DNS Packet

The DNS response against my domain is 1228 bytes long and I need the packet to get fragmented in 3 packets. To achieve this I have set the MTU at name server (bind9 running on the machine) to be 500. ...
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254 views

Linux route cache seems to load outdated settings

On SLES 11 SP3 (Kernel 3.0.101-0.46) I see the following route behavior: When I set a route specific MTU once via ip route change ... mtu lock 1500, everything works as expected (setting an MTU of ...
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ADSL router happily accepts IPv6 packets of 2K in size

As I understand IPv6 fragmentation, the routers do not perform fragmentation, only the end-to-end nodes do. And when any router along the path receives a packet larger than the MTU of the link to its ...
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MTU on server accidentally set to 0, can't ssh into it?

My server had some problem with the ssh and I couldn't upload files of size > 10 KB, as scp would hang during the copy. I found a solution for this problem here, and I was changing the MTU, when I ...