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Questions tagged [mtu]

For questions about or in relation to the maximum transmission unit (MTU).

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Pinging packets greater than 1500 between two proper configured machines on proper configured networks, always possible?

Given the following 3 subnet topology, I will give names to them to simplify it, I am using planets, I see it as a perfect geographic enumeration. Sites Office on Earth 172.1.x FiOS, default MTU ...
Sam Washington's user avatar
0 votes
2 answers
843 views

Is it safe to enable jumbo frames on switches in general

Can any harm occur by simply enabling jumbo frames on your switch infrastructure? I understand that in a given flow from one machine to another all participants need to support jumbo frames to arrive ...
ericx's user avatar
  • 153
0 votes
1 answer
72 views

IP fragmentation and PMTUD

I have 2 questions. 1) According to a lot of sources, when IP packets gets fragmented, in this case, lets take icmp, the icmp header is present only in the first packet. But I have observed on some ...
RRHS's user avatar
  • 405
0 votes
1 answer
54 views

Why MTU setting change not showing any meaning change in file transfer via tcp?

I performed a test in which I transferred a file of 1GB by opening a tcp port on destination server with MTU 1000. then I tried to change the MTU from 1000 to 9000 and the total time duration of 1GB ...
Vipin Kumar's user avatar
2 votes
2 answers
242 views

How can a router know the MTU of the next router?

https://www.cloudflare.com/learning/network-layer/what-is-mtu/ Suppose Server A and Computer A are connected, but the data packets they send to each other have to pass through Router B and Router C ...
NIOI's user avatar
  • 23
1 vote
2 answers
467 views

Brocade 7450 - set MTU to 9000

I have brocade icx 7450. I already enabled jumbo frames to increase MTU packets on switch. But unfortunately I am not able to change MTU size of port which I want. When typing after choosing interface ...
Frihu's user avatar
  • 13
0 votes
2 answers
151 views

Sanity Check: Changing MTU on Wifi Endpoints (computers) should be a LAST resort, right?

A client of mine has an organizational network that is comprised of a lot of Ubiquity gear, primarily switches and wireless routers to power their network, with a Sophos XG firewall at the border. ...
Thomas Ward's user avatar
0 votes
0 answers
10 views

What is the MTU used for in EIGRP? [duplicate]

A lot of sources mention that MTU is included in the EIGRP packets but is not actually used for any path selection calculations. I've also read somewhere that it was supposed to be used as a ...
Mitrixsen's user avatar
  • 803
0 votes
2 answers
846 views

GRE tunnel bridging and MTU mismatch

Background My workplace has 2 office areas which is only 200 meters away from each other. They have their own local networks, their own Internet connections, with routers configured to fallback to the ...
Livy's user avatar
  • 423
5 votes
2 answers
736 views

Can a jumbogram (giant data packet) be used at a large scale (in WAN for example)?

There are many scientific paper for Jumbo frame, even more, some real implementations and deployments. But it is not the case for Jumbogram !! Jumbo frame (geant frame) for Layer 2; Jumbogram (geant ...
Lee's user avatar
  • 63
2 votes
1 answer
609 views

What's the difference between MTU and MRU ? How come people talk so often about MTU and little consideration is given to MRU?

I don't understand why MRU isn't mentioned as frequently as its counterpart MTU. Are they always arranged to have the same value on a device ? A few days ago I noticed that my Windows machine accepted ...
Kode1000's user avatar
2 votes
1 answer
1k views

MTU mismatch scenario, two hosts handle in a different way ingoing packets bigger than local interface MTU. How does MTU really work?

I’ve been struggling with the MTU topic for a while and I still can’t get how it really works. The majority of books that I read and the courses that I attended all seem to treat this subject in a ...
Kode1000's user avatar
0 votes
2 answers
1k views

Does MTU setting affect sending, receiving, or both?

Consider the two devices: A: PC, NIC MTU is set to 1500 B: Router, MTU of relevant interface is 1478 Now if A sends a frame of length 1500 to B, something might go wrong. But what if I set A 's MTU to ...
user239216's user avatar
0 votes
0 answers
16 views

What is the maximum safe UDP payload size over IPv6? [duplicate]

I am developing a networking library (that uses exclusively UDP) and I want to support both IPv4 and IPv6 by using a dual-mode socket. I want to limit the size of the packet user can send to a value ...
FICHEKK's user avatar
  • 101
21 votes
5 answers
6k views

Why is Packet Size Limited?

I was reading: this answer to "Maximum packet size for a TCP connection", where it says: The absolute limitation on TCP packet size is 64K (65535 bytes), but in practicality this is far ...
Algo's user avatar
  • 313
0 votes
1 answer
876 views

Packet capture shows packets larger than MTU

I have been doing some tests with two CentOS computers located in a local network and I don't understand the results. We have a simple application where a client (x.y.z.204) sends text strings to a ...
chus's user avatar
  • 109
0 votes
1 answer
2k views

Help me understand why to decrease the MTU size

Why I should decrease MTU on interfaces instead of increase it when ipsec encapsulation is present, GRE or some other? The way I see it: a packet of 1500 bytes comes to the router, then there is IPSEC ...
Vladimir Fomin's user avatar
2 votes
1 answer
8k views

tcpdump output with bad length indicator present

Could someone help me interpret this tcpdump udp packet output? We are getting out image so I'm wondering why we are seeing this message. Is the packet length indicated by "length 1500)" or ...
simgineer's user avatar
  • 123
0 votes
1 answer
246 views

GRE, guarantee 1500 bytes MTU for end hosts

Is it possible to achieve 1500 byte MTU at the end host connections ignoring fragmentation overhead in this simple scenario using GRE. I would like to configure R1 and R2 to do the fragmentation ...
emirjonb's user avatar
  • 121
-1 votes
1 answer
1k views

Difference between MTU and max length of PDU [duplicate]

I was studying and came across the concept of MTU and I don't know how to differentiate it with the maximum length of a PDU. I understood that the max length of a PDU is the maximum amount of ...
ESCM's user avatar
  • 129
2 votes
1 answer
585 views

Difference beetween MTU, ipv4 MTU and mpls MTU

In a Cisco configuration, what is the difference beetween the MTU, ipv4 MTU and the MTU configured into the mpls section of an interface ? interface X mtu 9214 ipv4 mtu 9180 [...] mpls mtu 9200 !...
Eraseth's user avatar
  • 425
2 votes
1 answer
479 views

MTU changing after first ping

I noticed kind of strange behaviour and my knowledge doesn't have answer for it. So I want to know MTU. First ping: ping -c 1 -s 1800 -M do google.com PING google.com (216.58.209.14) 1800(1828) bytes ...
Nerwena's user avatar
  • 23
2 votes
2 answers
1k views

How exactly does Path-MTU Blackhole Detection work?

I'm currently trying to understand how the Path-MTU Blackhole Detection really works. From what I understand: You send rather big packets, starting at like 1460 Bytes (TCP example) and wait for ...
Gereon99's user avatar
  • 123
0 votes
1 answer
280 views

OSI model transition between layers (data chunking across layers)

There is something I don't understand regarding the OSI model. From what I learned, sometimes information will need to broken down into smaller pieces of information. My question is - let's say that ...
RandomAsker889's user avatar
0 votes
1 answer
417 views

routing MTU size and encapsulation?

I did some research for my question beforehand such as this one:Cisco routers THROUGHPUT - MTU and packet size however, it seemed not precise to explain the doubts in my head. My primary goal is to ...
user53815's user avatar
  • 123
1 vote
1 answer
603 views

how data are fragmented based on MTU and MSS?

just to be clear.. if a sender wants to send a data of 1800bytes ( assuming MTU be 1500bytes so MSS = 1500-40 (taking min ip and tcp header) = 1460bytes) Then there will be three segments 750 + 750 + ...
AxDu's user avatar
  • 13
2 votes
1 answer
2k views

Vxlan with internet access - possible because of high MTU?

So i was wondering, because VXlan requeres a high mtu to work properly (some set it even as high as the max configurable MTU (9000ish)), how would providing internet access for these nodes/servers ...
Loco's user avatar
  • 25
1 vote
3 answers
3k views

Minimum MTU size on Ethernet and minimum Ethernet frame size

I am a bit confused about the understanding of the relationship between minimum MTU of MTU and minimum Ethernet frame size. We know that the maximum MTU of Ethernet is 1500 Bytes which makes the ...
ERH7777777's user avatar
2 votes
2 answers
1k views

Confusion about MTU

I am studying about IP fragmentation and MTU. What I know is MTU is the property of Physical medium, as in the amount of data it can process without having to fragment the data. The default MTU on ...
Techievent.in's user avatar
1 vote
1 answer
276 views

MTU size for PPPOE with QinQ

i used at as A pppoe server i have used QINQ secend tag in rotuer interface TenGigabitEthernet2/0/0.904 description Cust1-QINQ encapsulation dot1Q 904 second-dot1q any pppoe enable group PPPOE-...
Anas Programmer's user avatar
2 votes
1 answer
2k views

MTU mismatch in the network

The issue is on our routed network for one site to another.. The clients can't access a secure routed websites.. Simply the DNS server will resolve but the web page will not load.. All our server and ...
user65285's user avatar
0 votes
1 answer
3k views

Create a VXLAN with MTU = 1500?

I have a cluster of servers interconnected with 10 Gbps fabric interfaces (ens1f0, MTU 1500). I've set up a VXLAN interface across the cluster using default settings (MTU 1450). For reasons of ...
iBug's user avatar
  • 205
2 votes
2 answers
1k views

MTU the most Confusing Networking term. Lot of questions

I have ton of questions and i feel this is most confusing term for me. The more i read the confusion deepens. I am not able to connect dots. please help. Do we need MTU adjustment with EoMPLS/dot1q ...
Terminator's user avatar
2 votes
2 answers
1k views

Question about MTUs vs maximum frame sizes - what is their difference?

I am currently studying networking at university and I have a question about MTUs and maximum frame sizes. What is the difference between the MTU and the maximum frame size? This Wikipedia article ...
mariaprsk's user avatar
  • 165
4 votes
2 answers
940 views

Confusion about data fragmentation/MTUs - why was it introduced in the first place?

I am currently studying networking as a part of my bachelors and I am a bit confused about why fragmentation/MTUs are necessary. In my lecture slides, it only says "Fragmenting if necessary" under the ...
mariaprsk's user avatar
  • 165
1 vote
2 answers
14k views

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 - ...
yael's user avatar
  • 11
2 votes
1 answer
2k views

Which interfaces do I need to configure to change MTU of Cisco Site-to-Site VPN

I have a number of Site-to-Site VPN tunnels in my network configurations. They are configured using Cisco ASA devices. To resolve some performance issues I am trying to change the MTU for traffic ...
Stringers's user avatar
3 votes
2 answers
2k views

How do both sides know the MTU

If I have ComputerA that has their networking interface set with an MTU of 1500 and ComputerB has a network interface with an MTU of 1200 is there any way for ComputerA to know that ComputerB's MTU is ...
Dovid Bender's user avatar
0 votes
1 answer
71 views

How does a router calculate a MTU [duplicate]

For a given link type, how would a router calculate it's MTU? I initially thought of it taking a brute force approach, using a binary search to figure out the point at which the link fails to support ...
Tobiq's user avatar
  • 213
4 votes
2 answers
5k views

Difference between Giant Frame and Jumbo Frame

Can someone enlighten me the difference between Giant Frame and Jumbo Frame? From what I hear, Giant frame is a frame with the size greater than 1518 Bytes excluding Preamble, Frame Delimiter and ...
KingsNeverDie's user avatar
1 vote
1 answer
629 views

why mtu cmd ping test result depends on mtu setting on router?

why MTU test results depend on MTU setting on my router??. ex: when I set MTU on my router for 1440, the result is "1440-28=1412", the first MTU gives replay, so how can I know the best MTU??.
Möştafa Ahmed's user avatar
3 votes
1 answer
1k views

What happens if the IP MTU is smaller than the MSS?

Let's say i configure the MSS > IP MTU. Even if it doesn't make sense, would this be possible? Assuming i then try to send a file of the size of MSS or bigger, the network layer will receive the data ...
 Chinchillo's user avatar
12 votes
2 answers
15k views

Why maximum length of IP, TCP, UDP packet is not suit?

From many tutorials, I get follow knowledge(maybe I'm misunderstood) : maximum of an Ethernet packet is about 1500 bytes. maximum of an IP packet is about 65535 bytes. maximum of a UDP packet is ...
Shuai Li's user avatar
  • 261
3 votes
1 answer
698 views

What does MTU depend on?

I'm trying to understand what factors determine the MTU. For instance, why 802.11 has MTU of 2304 while Ethernet MTU of 1500? Are there restrictions of the physical medium or arbitrary design ...
Vasilis's user avatar
  • 427
4 votes
2 answers
3k views

Nexus 3172T MTU

I am attempting to set the L3 mtu on a Nexus port. The mtu option is only available if I set "no switchport" which then prevents me configuring VLAN related settings. Am I missing something obvious? ...
B. Austin's user avatar
  • 127
6 votes
2 answers
1k views

How does a router know the MTU of a network?

I've done several exercises where you're given the MTU of a net or subnet, but I wonder how routers know the MTU of the nets they're connected. I've learnt that in OSPF protocol this information is ...
Josemi 's user avatar
  • 185
1 vote
0 answers
4k views

Fragment Table Overflow router cisco (strange Behavior) [closed]

I am getting this error message many times in my Router Cisco : %IP_VFR-4-FRAG_TABLE_OVERFLOW: Tunnel1: the fragment table has reached its maximum threshold 16 %IP_VFR-4-FRAG_TABLE_OVERFLOW: Tunnel1:...
Mamitiana Ra's user avatar
1 vote
1 answer
934 views

Advantages of setting the MTU and MRU at the server-facing port?

Let's say, that one has a following network topology: www-server[eth0] <-> [ge-0/0/0]MX-router[ge-0/0/1] <-> Internet What are the advantages of setting the Maximum Transfer Unit and ...
Martin's user avatar
  • 1,063
3 votes
1 answer
432 views

Cisco 3560 Jumbo Frame

looking for some clarification on the jumbo frame config for a cisco 3560 switch. I understand that by enabling jumbo frames, it enables it on all ports for entire switch, what happens to devices ...
Igor P.'s user avatar
  • 31
13 votes
2 answers
8k views

Is the MTU of Ethernet still 1500 Bytes?

So basically do the modern routers in the internet still use 1500 as the MTU of Ethernet? or the 1500 Byte was for the old days? What I'm asking here is what is the MTU of Ethernet in modern Networks?...
John P's user avatar
  • 531