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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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How do I view cached PMTU under Linux (and all other OSs)

When I ping a remote site with the DF bit set and a packet size that is too big for my router the first ICMP "fragmentation required" message is sent from the router. After that the message comes from my localhost. Netstat -rC (on Linux) allows me…
Neik
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How do I prevent TCP connection freezes over an OpenVPN network?

New details added at the end of this question; it's possible that I'm zeroing in on the cause. I have a UDP OpenVPN-based VPN set up in tap mode (I need tap because I need the VPN to pass multicast packets, which doesn't seem to be possible with tun…
Jason R
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What is the "in-the-wire" size of a ethernet frame? 1518 or 1542?

According to the table here, it says that MTU = 1500 bytes and that the payload part is 1500 - 42 bytes or 1458 bytes (<- this is actually wrong!). Now on top of that you have to add IPv4 and UDP headers, which are 28 bytes (20 IP + 8 UDP). That…
chrisapotek
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OpenVPN: How to mitigate path MTU issues on a per-client basis?

We have dozens of embedded devices installed at customers, all calling home to our OpenVPN service. That works fine in general, but a few of our customers have severe path MTU issues. Our influence on the customers to fix their networks is limited,…
Nils Toedtmann
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How is the MTU is 65535 in UDP but ethernet does not allow frame size more than 1500 bytes

I am using a fast ethernet of 100 Mbps, whose frame size is less than 1500 bytes (1472 bytes for payload as per my textbook). In that, I was able to send and receive a UDP packet of message size 65507 bytes, which means the packet size was 65507 +…
nikku
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Why does lowering the MTU from 1500 to 1499 allow me to access most websites?

I had this issue where I was only able to connect to websites like google.com and ibm.com when the mtu was set at 1500, but if I tried to connect to anything else, it would just show a blank page. When the mtu was lowered to 1499, it started…
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Are Jumbo Frames (MTU up to 9k) realistic/common over the open Internet?

I've got an application that would benefit from larger Ethernet frames. (In theory, we could reduce the number of outbound packets by > 50%, maybe even 66%.) I'm also in the process of specifying networking requirements with candidate hosting…
Stu Thompson
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What am I misunderstanding about calculating MTU?

Okay, I just finished resolving a jumbo frames issue between a few Xserves, a Netgear GSM7224, and a Drobo B800i. It turned out that the Xserves (Mac OS X 10.6.8 Server) and the Drobo B800i accept the MTU in bytes as normally expected (1500-9000),…
morgant
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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) or my RaspberryPI2. I deactivated encryption…
Alexander Theißen
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Does setting MTU on logical interfaces affect physical interfaces

I've been using a combination of interface bond-, vlan- and bridge-interfaces to provide redundancy and different logical network layers to xen domU's. This setup is working well however i'm a bit uncertain as to how different settings on these…
KvH
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Jumbo frames between KVM guest and host?

I am trying to implement a 9000 byte MTU for storage communication between KVM guests and the host system. The host has a bridge (br1) with a 9000 byte MTU: host# ip link show br1 8: br1: mtu 9000 qdisc noqueue…
larsks
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MTU on mobile data networks

I found various lists of MTUs for different links, but they never contain UMTS, LTE, EDGE, HSPA, GPRS. What are the MTUs of the above mentioned technologies?
bot47
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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 tcpdump (see here)) But if I capture now with…
der_wolle
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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 tried posting this under that as an answer for…
Atomo
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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 accidentally did sudo ip link set eth0 mtu 0. No one…
Bharadwaj Srigiriraju
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