Questions tagged [mtu]

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

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Is transport layer MSS dependent on Ethernet MTU? [duplicate]

Ethernet has an MTU of 1500 bytes whereas IP has a maximum length of 65535 bytes. It might seem that the average TCP segment that is lesser than the IP maximum length or the Ethernet MTU has to be ...
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20 votes
5 answers
3k 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 ...
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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 ...
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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 ...
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2 votes
1 answer
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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 ...
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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 ...
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-1 votes
1 answer
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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 ...
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2 votes
1 answer
141 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 !...
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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 ...
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1 vote
2 answers
252 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 ...
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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 ...
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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 ...
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1 answer
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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 + ...
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1 answer
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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 ...
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3 answers
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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 ...
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2 votes
2 answers
511 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 ...
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1 vote
1 answer
178 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-...
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1 answer
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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 ...
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1 answer
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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 ...
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2 answers
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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 ...
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1 vote
1 answer
363 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 ...
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4 votes
2 answers
842 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 ...
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1 vote
2 answers
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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 - ...
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2 votes
1 answer
938 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 ...
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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 ...
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0 votes
1 answer
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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 ...
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3 votes
2 answers
3k 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 ...
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1 vote
1 answer
442 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??.
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3 votes
1 answer
944 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 ...
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8 votes
2 answers
10k 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 ...
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3 votes
1 answer
602 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 ...
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4 votes
2 answers
2k 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? ...
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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 ...
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1 vote
0 answers
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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:...
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1 vote
1 answer
810 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 ...
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3 votes
1 answer
354 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 ...
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13 votes
2 answers
7k 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?...
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  • 481
2 votes
3 answers
10k views

Verifying current network MTU sizes

Hello Network Engineers, I've been tasked with identifying weather or not my current network has (egress / ingress) MTUs greater than 1400. My question is, what is the best method of capturing/...
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4 votes
1 answer
267 views

Can the MTU size change on a local network if non of my software attempt to do that?

From the ip manual page (man 7 ip), we read that the MTU may change over time. When PMTU discovery is enabled, the kernel automatically keeps track of the path MTU per destination host. When it is ...
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5 votes
2 answers
252 views

Is Path MTU Discovery(PMTUD) really efficient?

As i know, PMTUD uses ICMPv6 to find minimum MTU value in the network path. I understood why IPv6 doesn't allow fragmentation (by reading this article), but PMTUD doesn't look like good manner. here ...
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4 votes
2 answers
532 views

Why are Internet hosts "not required" to receive an IPv4 datagram larger than 576 bytes?

I'm currently studying Internet protocols and had a question regarding the IP datagram. Within the IP header I am aware there is a field called "total length" which specifies the total ...
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2 votes
1 answer
2k views

About BEST and MAX MTU with PPPOE + PPTP

About BEST and MAX MTU with PPPOE + PPTP in the router. I have Has been setup WAN to PPPOE and MTU is 1492, because 1464 is maxed on my ISP. and I have connected PPTP on the same router, and MTU is ...
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2 votes
2 answers
8k views

Cisco ASA MTU vs TCP MSS

I am trying to set jumbo MTU for Cisco ASA 5585 and I did following: asa1/pri/act(config)# mtu inside 9000 INFO: Jumbo frames should be enabled to receive packets more than 1500 MTU Use '...
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6 votes
2 answers
513 views

how to find the right value of MTU Jumbo frame

we take the decision to set jumbo frame on all our linux machines we have hadoop cluster with master machines , workers machines and kafka machines our switches ( Cisco ) are suitable to Jumbo frame ...
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  • 61
2 votes
1 answer
1k views

MTU size for new datacenter

What appropriate MTU size should be used in datacenter switches and routers? is there any standard or pros and cons? Default is 1500 but that isn't enough to push data. should we used 9000 MTU on ...
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  • 4,227
3 votes
2 answers
2k views

Cisco routers THROUGHPUT - MTU and packet size

I am researching the throughput of my Cisco routers. For now I know that throughput depends from packet size and configured services like NAT or ACL filtering. My question is about packet size. For ...
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1 vote
1 answer
2k views

MTU 1500 gigabit connections translated to 9000 jumbo packets over 10 gigabit connection

I'm testing the frame size by adjusting it from 1500 to 9000 for the link to the storage NAS to optimize the 10 gigabit connection and have seen an increase of speed to almost 300% read speeds. I ...
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  • 259
3 votes
1 answer
1k views

Why is the Ethernet data frame size limited to 1500 bytes?

I am still not sure why the Ethernet data frame size / MTU was set maximum to 1500 bytes. I found out a document from Xerox which is from 1980. Available at (http://www.pennington.net/archives/...
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2 votes
1 answer
73 views

Do packets take the same amount of time when they are within the MTU?

Without considering application processing or deep packet inspection, do packets that do not fragment all travel through the network at the same speed? For example, if there is a network with an MTU ...
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  • 21
1 vote
2 answers
2k views

Is it possible to enable jumbo frame only on some interfaces of CISCO WS-C2960X-24PS-L

We want to enable 9K jumbo frame on CISCO WS-C2960X-24PS-L switches, however I found this line in the documentation and it made me confused and concerned because it involves reset and reload of switch ...
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