MTU (Maximum Transfer Unit) refers to the largest size of the datagram that a layer of a communication protocol can transmit.
Questions tagged [mtu]
77 questions
23
votes
5 answers
How to tell what MTU is being used in Windows XP
I'm suffering from a really weird problem where I randomly get "The connection to the server was reset" errors when trying to access web pages (HTTP error 12031 according to the Windows network diagnostic tool) - this happens regardless of whether…
andygeers
- 343
11
votes
1 answer
Windows 7 doesn't request MTU from DHCP server; what is it thinking?
My computer's Ethernet adapter uses 1,500 byte Ethernet frames. Normally this means that my Local Area Connection's MTU is 1500 bytes.
But my (IPv4) connection to the Internet has some overhead. This means that my actual MTU when communicating to…
Ian Boyd
- 23,066
10
votes
6 answers
Why does Mac OS X insist on changing my MTU to 1500?
Recently (I think after updating to 10.6.4) Mac OS X has insisted on changing my MTU to 1500, even though the router which my Mac connects to directly has an MTU of 1472. I've noticed that manually setting the MTU to 1472 drastically increases…
Ritwik Bose
- 888
4
votes
1 answer
MTU setting ignored by Java socket on loopback
I've got a mtu problem. I did the following:
root@sa-headend:/home/sa# ifconfig lo mtu 1500
root@sa-headend:/home/sa# ifconfig lo
lo Link encap:Lokale Schleife
inet Adresse:127.0.0.1 Maske:255.0.0.0
inet6-Adresse:…
Simon Ottenhaus
- 155
4
votes
3 answers
About MTU settings in machines and switch
Suppose I have two machines and one switch.
M1--Switch--M2.
The settings are:
M1 has MTU set to 100
Switch has MTU set to 1000
M2 has MTU set to 1000.
Questions:
When M1 tries to send a 100-byte packet to M2, there should be no problem,…
performanceuser
- 231
- 1
- 3
- 7
4
votes
2 answers
How iptables "--clamp-mss-to-pmtu" calculates PMTU?
I have seen in many places this iptables rule iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu to deal with Path MTU Discovery issues.
From my understanding, PMTU may differ in multiple paths (say A->B has PMTU 1400,…
coherence73
- 43
4
votes
1 answer
How to change MTU without ifconfig in ubuntu 18.04?
I need to change the MTU size in my newly installed ubuntu 18.04. This can be done with ifconfig.
But i can not install ifconfig. Whenever i run command sudo apt install net-tools i get the following errors.
Err:1 http://archive.ubuntu.com/ubuntu…
mahfuj asif
- 143
3
votes
3 answers
Can't access some websites, possible MTU issue on the router?
Two particular sites that I can't access at all is css-tricks.com and jquery.com which are pretty crucial to me since I'm a web designer.
I talked with my ISP and we tried
Using different browsers,
Using various dns servers,
Clearing the DNS…
user97114
3
votes
1 answer
Why is the TCP MSS (Maximum Segment Size) 1460 bytes?
Why is the MSS 1460 bytes max in a TCP data packet?
Data packet
Image source.
I know that:
The MTU for Ethernet networks is 1500 bytes max.
The IP header is 20 bytes.
The TCP header is 20 bytes.
But still, why 1460 bytes? Couldn't it…
Dacaramo
- 35
3
votes
1 answer
Why do I see Ethernet frames that exceed the MTU+Ethernet header size?
I have a consumer-grade Wi-Fi router that hosts a local network. The router is connected to the Internet through a campus network (i.e., an Ethernet cable connects the WAN port to a campus Ethernet plug). I'm running tcpdump on the router's WLAN and…
Janus Varmarken
- 131
3
votes
1 answer
Separate MTU for IPv4 and IPv6 on Linux
Is it possible to define MTU on an interface with different values for IPv4 and IPv6 on a Linux machine?
It seems that command ifconfig MTU defines the same MTU for both IPv4 and IPv6.
Any help is appreciated.
Gaston
- 131
2
votes
2 answers
Drop IP fragments of a certain protocol
When conntrack is active, the iptables stack never sees a fragmented IP packet, only the reassembled one (source), so the -f test never matches.
If I want to block any fragment I could set ipfrag_high_thresh or
ipfrag_time to 0 (source), but that…
Lorenzo Pistone
- 454
2
votes
1 answer
What is the most MTU efficient way of creating a network tunnel?
I am currently using SSH tunneling to connect to the internet via a remote computer using the -D ssh argument. I've recently run across a problem with this solution -- the SSH protocol decreases the MTU significantly. I'm not at all worried about…
2
votes
0 answers
What's the maximum MTU for Wi-Fi 6 (802.11 ax)?
The only thing I found about "Wi-Fi 6 MTU" are old posts about the old standards. Wi-Fi 6 is new and has higher speeds where higher MTUs are more suitable than in slower networks.
Does Wi-Fi 6 support more than 2304 bytes?
Mikael Dúi Bolinder
- 2,230
2
votes
0 answers
My syslog is full of errors from NetworkManager about setting the MTU for wireless adapter
NetworkManager keeps trying to set the MTU for my wifi connection to 9216 and then complain about it:
NetworkManager[9173]: [1469713916.019478] [platform/nm-linux-platform.c:2489] sysctl_set(): platform-linux: sysctl: failed to set…
dovetalk
- 233