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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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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 Hub Linksys SPA2102 VOIP router These devices are…
jdog
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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 installing it. As a result my server will switch the…
mal
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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"; the same phenomenon occurs for that protocol. A…
David Tonhofer
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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 some users access this via a NAT firewall and ...…
Jesús Couto Fandiño
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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 from socket failed: Software caused connection…
rev
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Permanently set MTU on Ubuntu 14.04 machine within an Amazon VPC

I have some Ubuntu 14.04 machines running in an Amazon VPC. When they start, they have an MTU of 9001, but this appears to cause some problems when communicating with other servers which have an MTU of 1500. When I use ip link set dev eth0 mtu 1500…
Paul Dixon
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XenServer 6.2 changing mtu

So I've looked around for a way to change the MTU of interfaces on XenServer 6.2, but can't find anything that works for me ... One method spoke about changing the ifcnfg-intX files in the /etc/sysconfig/network-scripts directory, but the files just…
Just Lucky Really
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Maximum MTU size

Thought one of the issues I'm experiencing with the following question is due to MTU rightfully so. ESXi 5 VM Putty session hangs, vSphere client timing out However, when I tried testing the maximum MTU size it seems there's just no limit. Thought…
user192702
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MTU value causing applications to hang

I am using CentOS 5 in my environment and it acts as a gateway for my LAN. My eth0 interface MTU is set to 1500 (default). UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Recently I am facing a strange problem where some of the websites simply…
Supratik
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Can fragments of a packet be refragmented again?

In IPv4, fragmentation is done by routers on way to the destination if DF(do not fragment) flag is not set in the IP packet. Once a packet is fragmented, its fragments may take different paths (due to various reasons like topology changes) to the…
gsinha
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other than manually changing it, how is MTU set?

I recently discovered a Windows 7 client that couldn't connect to one of our servers. It turned out the problem was both that the server was set for an MTU of 1514 and that the client was set to 1504. The server runs CentOS and grep -i MTU…
rymo
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Getting interface MTU under Linux with PCAP

I am interested in storing packets I sniff using PCAP. As I preallocate the memory I need - i.e. a multiple of the MTU of the interface I am sniffing from, I would like to discover how much memory I need before opening the live session. Is it…
ziu
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VMWare ESXi 4.1 VMXNET Ignoring MTU and Sending Jumbo Frames

On my CentOS 5.6 ESXi 4.1 VMs using VMXNET, it looks like they are attempting to send jumbo frames: However, all the interfaces are set to MTU 1500. What is causing this behavior? Update: I would think that regardless of the switch, wouldn't…
Kyle Brandt
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Why do I see an IP packet with size 2960, way above the MTU setting of 1500 on the interface and it gets through?

I am analyzing traffic between a client and a Linux webserver running on a HP blade server, the client sometimes gets stuck waiting for more data when the webserver has closed the connection. The webserver runs apache2 that for some reason choses to…
ernelli
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Optimal MTU settings ADSL for PPPoE over ATM/LLC

Is 1446 optimal for PPPoE over ATM/LLC as this forum post describes?
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