Questions tagged [mtu]

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

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83 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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2answers
841 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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1answer
23 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 ...
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1answer
709 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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1answer
69 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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1answer
354 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 ...
3
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1answer
416 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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2answers
648 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? ...
6
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2answers
990 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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0answers
156 views

Fragment Table Overflow router cisco (strange Behavior)

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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1answer
342 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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1answer
130 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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2answers
5k 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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3answers
4k 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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1answer
212 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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2answers
220 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 ...
5
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2answers
285 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 length of the ...
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1answer
667 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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2answers
4k 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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2answers
412 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 ...
2
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1answer
754 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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2answers
1k 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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1answer
1k 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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1answer
734 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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1answer
62 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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2answers
1k 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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1answer
611 views

Question regarding MTU settings on a Cisco 3750X Switch

I have a Cisco 3750X switch stack (2 switches stacked) and have a Compellent and three Equalogics as well as three VMware hosts directly connected but separated via different vLANs on this switch. The ...
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3answers
10k views

Increasing the MTU size for 3G/LTE networks

Is it reasonable to set higher MTU size between RAN (3g, LTE) and RNC/SGW? Say, we have S1-U interface with GTP encapsulation, which leads to reduced data size for mobile user. Data size can be ...
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1answer
288 views

Regarding clns mtu

I understand the below points,please confirm if my understanding is correct. MTU > MSS E.g if my MSS is 1460 bytes, then MTU should be at least 1500 bytes(20 bytes for IP header and 20 bytes for TCP ...
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0answers
34 views

Does increasing the FEC decreases the payload in the maximum packet size?

we can find the maximum packet size by the formula packet err rate = 1 - (1 - bit err rate)^(max packet size) so does this max packet size include the FEC bits? I assume this formula gives the max ...
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1answer
147 views

What happens when an intermediate hop router encounters a packet whose MTU size is more than what it can handle?

Basically if the frame size of a packet is more than the MTU size configured in the router (which is an intermediate hop) the packet is dropped. Since IP does not have any ARQ mechanism, is there a ...
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1answer
449 views

Override Interface MTU [closed]

I'm currently investigating an unusual MTU issue. I have a server running Red Hat with a single interface which has an MTU of 1500. I have verified this by running netstat -i. When I packet capture ...
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1answer
652 views

What should a device do with an Ethernet frame larger than its MTU?

When I test with Cisco 2960 series switches or with ISR routers, then if port receives an Ethernet frame larger than its MTU value seen in sh int output, then device drops this frame and increases the ...
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1answer
2k views

Setting system jumbomtu on Cat 6500

We have an L2 path between a tape drive and a NetApp. The path goes through 3 switches (a 6509 and two N5K) but the two devices are on the same VLAN. All 10 gig fiber. I found out that while most of ...
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1answer
722 views

Jumbo frame on Nexus 5k

I would like to enable the jumbo frame support on my N5k for specific SCSI trafic. I've read we can't do it per interface but only on the system itself : policy-map type network-qos JUMBO_MTU ...
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1answer
5k views

Why is the minimum MTU of a IPv4 packet 68 bytes?

According to RFC791: Every internet module must be able to forward a datagram of 68 octets without further fragmentation. This is because an internet header may be up to 60 octets, and the minimum ...
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1answer
286 views

Change MTU without infrastructure change

It's very strange issue, on openstack cluster we have VxLAN between network and compute node and its using 1450 MTU (1500-50) because of encap header. Because of it some of my application not working ...
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1answer
398 views

What does limit a MTU set for an interface? [closed]

The maximum MTU I can set is between 9000 an 10,000 for a Ethernet interface. I have the following message for high values ifconfig eth0 mtu 10000 SIOCSIFMTU: Invalid argument What is the origin ...
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1answer
173 views

What is the mathematical relation between MTU size and the number of LSA supported in OSPF?

Improved my calculation - based on the comments. However,I don't get the correct results yet. I am trying to find out the maximum number of stub LSA routes I can pass from one device to another ...
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1answer
4k views

TCP segment length and TCP/IP header options

MSS are calculated as MSS = MTU - IP header length - TCP header length. One example is MSS=1500-20-20=1460 in Ethernet. This calculation neglects the options in TCP and IP headers, which lead to ...
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1answer
426 views

UDP and fragmentation calculation

Assume we have a ethernet link with an MTU of 1300 bytes, while an application want to send 5200 bytes of data. How many fragments do we transmitted ? i would say 5, to send 5200 bytes over a link ...
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2answers
312 views

Do MSS/MTU violate the protocol stack layers independence?

We studied that the beauty of internet protocol suite layers is that each layer is responsible for a piece of the communication process. These layers provide services to adjacent layers and operate ...
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2answers
7k views

What is the 802.11 MTU?

I keep reading it is 2304 bytes. Wikipedia states it is 7981 bytes. On my WiFi AP, I can set the RTS threshold with a value of 0-2346 bytes (I guess it's MTU + the MAC/PHY header ?) Where does this ...
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2answers
241 views

rfc1918 address in WAN point-to-point link

What will be the issue if we use rfc1918 private IP address range /31 or /30 in point-to-point link? [ISP]--------------[Router1]------rfc1918--------[L3 Switch]-------[LAN] I heard PMTU can be ...
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1answer
1k views

What is 576 bytes and 68 byte chunk when it comes to MTU?

I know these numbers are related to the MTU size but I did not get a clarity of what exactly it is and why this number.Could anyone please explain?
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89 views

How do these packets know what size to be?

The smallest MTU between the source and destination is 600. What I don't understand is how TCP knows to only include a max of 548 bytes, so that it doesn't go over 600 with TCP and IP overhead. MTU ...
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1answer
120 views

Cisco restrict MTU size

Is there an any option in cisco Router we can restrict MTU size to something smaller? default is 1514 but for experiment i want to allow 512 only and if packet if bigger than 512 discard them.
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1answer
452 views

Manual setting MTU still needed today?

Symptom ssh to remote-host works. Simple output like ls works. But more output like find / fails. Solution In our case we reduced the MTU to 1200 on eth0 (IPv4) and the symptoms disappeared. ...
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2answers
2k views

MTU affects access to some sites [closed]

I'm no expert in this field, so I thought I would come on here and get some opinions. I have issues accessing certain websites, one example is codility.com. As I understand it (and correct me if I ...
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1answer
772 views

More Fragment flag and Frag Offset field after GRE fragmentation

If the length of a packet by attaching GRE-IP header results in bigger size than router MTU, what happen on More Fragment Flag and Frag Offset field of that packet?