Questions tagged [fragmentation]

For questions about packet fragmentation in a computer network. For instance, you are troubleshooting a case, where a network device encounter packet loss; and reliable protocols such as TCP must retransmit all of the fragments in order to recover from the loss of a single fragment.

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Can MAC fragmentation improve throughput fairness in 802.11?

If I fragment data on the MAC layer, can I improve the throughput fairness in 802.11? Initially, I thought so, because if a client always sends very long frames and another client always sends short ...
leonboe1's user avatar
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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 ...
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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
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Can a switch fragment a jumbo frame?

In all resources seen that tackle the term of "jumbo frame", I understand that it is applied in a LAN, because: It's a Jumbo frame, and a frame is for Layer 2 These resources talk a lot ...
Lee's user avatar
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3 votes
1 answer
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Does the MSS (Maximum Segment Size) prevent IP Fragmentation in all cases?

I have read that the MSS (Maximum Segment Size) is used to prevent IP Fragmentation. Now if the two communicating devices exist on the same network, and this network have a MTU (Maximum Transmission ...
user4582812's user avatar
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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
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2 answers
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What should we do if the number of bytes to be transferred are not in multiples of eight in ipv4? [duplicate]

(it is take from book called special edition tcp ip, pic taken for better formatting and ease to read) Theory that I am trying to understand-: So i found a question that is relevant to this-: ->a ...
hibweu's user avatar
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Fragments taking different routes?

I have trouble understanding why sometimes it occurs that during IP fragmentation certain fragments take different routes. I was following this the second example: https://www.gatevidyalay.com/ip-...
mato_kan's user avatar
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1 answer
255 views

Router could get packet of size more than 1500 bytes?

Suppose transport layer get the segment 4000 bytes from application layer at sender site. But we know maximum MTU in layer2(Ethernet) is 1500 bytes. My question is so fragmentation is happening at ...
S. M.'s user avatar
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Can I set fragmented IPv4 packet's DF bit to '1'? [duplicate]

If make DF to 1, can I confirm that fragmented packet with DF=1 will go through routers to the dest IP without any reassembly and re-fragmentation?
lee yk's user avatar
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How to create a mapping between TCP segments or IP packets or fragments and TCP Windows? [closed]

I am searching for a method how I practically can determine the segments within a TCP window both when sending and receiving them? I want to modify IP packets per TCP window. I already looked into the ...
kaiya's user avatar
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How to send 10-20KiB with UDP semantics? [closed]

I have volatile traffic, of 10-20KiB, that I want to send with UDP semantics. I have measured packet loss between several servers across the internet. In testing, I can reliably get 32KiB UDP packets ...
fadedbee's user avatar
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658 views

Can Ethernet frame be fragmented?

If there is IP fragmentation, is there also Ethernet fragmentation? I tried to google it but there seems to be no such thing. So what if, for example, we encapsulate Ethernet into ATM, what would the ...
Noob_Guy's user avatar
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17 votes
3 answers
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Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?

Why does one say fragmentation is bad and must be avoided due to performance issues when in reality fragmentation intrinsically occurs within the communication ? Example: User1 wants to send 100 000 ...
Floji's user avatar
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rules regarding IPV4 fragments and piecing them together

I'm rolling off my own TCP/IP stack for DOS and I have a question on IPV4 packets. Assuming that a client sends multiple IPV4 fragments, I would predict the MF flag would be set for every fragment ...
Mike's user avatar
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3 votes
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659 views

Is it possible get fragmented if the packet size is less then MTU?

I'm writing a socket application that is running on Linux. My server machine is connected to a switch that is connected to a network. There are also other servers connected to the switch. My client ...
user73869's user avatar
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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 + ...
AxDu's user avatar
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How is ICMP Packet Too Big handled in IPv6?

I am trying to comprehend the way packets fragmentation works in IPv6. As far as I understand it, IPv6 routers never fragment packets: upon receiving a packet whose size is bigger than the MTU of the ...
Nikita Tkachenko's user avatar
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2 answers
324 views

why ip protocol use fragment offset instead of index number?

I was wondering why the IP protocol use fragment offset to define the fragments of an IP datagram instead of using index number (first fragment with index 0, second with index 1, ...). We already know ...
MohamedLEGH's user avatar
4 votes
2 answers
939 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
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Typical signs of fragmented IP fragments

Given, for example, a Wireshark trace, how can I identify that the IP fragments that I am sending are themselves being fragmented? For example, if I'm sending 1500 byte IP fragments, and the server ...
Drayden J's user avatar
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1 answer
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Which IPv4 options must be copied on fragmentation and why?

In RFC 791 page 14 it says The copied flag indicates that this option is copied into all fragments on fragmentation. 0 = not copied 1 = copied If I understand correctly it is possible to specify ...
Niklas Rosencrantz's user avatar
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2 answers
13k views

What's the DF flag mean in IP packet header?

In the IP package, there is DF flag: Don't Fragment. I have doubt about it, is it mean let all the L3 device do not to fragment the IP packet (if the L3 device found it is bigger than MTU, device ...
244boy's user avatar
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3 votes
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Why the IPv4 need Don't fragment Flag?

Why the IPv4 need Don't fragment Flag? We know the IPv4 Flags options are: Reserved bit, Don't fragment, More fragments, fragment offset options. Why there need the Don't fragment Flag? if it is ...
aircraft's user avatar
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How to understand the Flags is IP_MF, what will happen?

For data packets whose length exceeds the MTU of the interface, fragmentation processing is required. The fields related to fragmentation in the IP header are as follows: Identification - Used to ...
aircraft's user avatar
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Scaling fragment offset

I studied that fragment offset has 13 bits. At transport layer segmentation is done considering the the MTU at lower layers (network layer, data link layer). Ethernet format says the maximum data ...
Venugopal's user avatar
2 votes
1 answer
596 views

Why does TCP need segments if the network layer automatically breaks things up into fragments?

I'm trying to better understand the difference between IP fragments and TCP segments (https://www.shubhsblog.com/tech/difference-ip-fragmentation-tcp-segmentation.html) and there's one thing I'm not ...
Dave's user avatar
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6 votes
2 answers
3k views

How does a TCP segment fit into a smaller IP packet?

The IP protocol can handle fragmentation and it includes the fragmentation offset and identifier. I know this comes into play when your IP packet is too big for some specific network or link where the ...
Lucas's user avatar
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2 votes
1 answer
4k views

Can I force a higher TCP segment size with netcat?

I'm using netcat to send random data from A to B, both Linux machines on Ethernet networks, with a router in the middle. For pedagogic purposes I'd like to force IP fragmentation on the router (Cisco ...
Eusebius's user avatar
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2 answers
356 views

Where is the data fragmented into pieces, and based on what rule?

When data from the application layer pass to transport layer: data may be fragmented into pieces of data, and then the transport layer will be added to the transport layer header (may be TCP header, ...
aircraft's user avatar
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2 votes
1 answer
1k views

Junos IPSEC Tunnel to Azure & TCP-MSS

I am configuring a Juniper SRX 300 Series to establish an IPSEC tunnel to Azure. The Azure Vnet range is 192.168.10.0/23 The local range is 10.49.236.0/24. The configuration: (relevant bits with ...
Aaron Tate's user avatar
2 votes
2 answers
1k views

TTL used during fragmentation

Hypothetical case Let's say router (R1) receives a IP datagram of length:820 (header + payload) with TTL:255, and ID:11. The outgoing link has an IP-MTU of size 420. Now R1 has to fragment the ...
Vivek Maran's user avatar
4 votes
1 answer
418 views

Why do we need to use "Service Disable-ip-fast-frag" command in Cisco Router ?

What is the benefit by Disabling " IP particle-based fast fragmentation " service on Cisco routers ? Thanks in Advance, Sajith
Sajith S.K's user avatar
1 vote
1 answer
1k views

Understanding how IP Reassembly Process works

I'm trying to understand IP fragmentation and reassembly processes well. I found this example on the Internet that I guess would be useful to understand the topic. Suppose a certain computer recieves ...
Tendero's user avatar
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-1 votes
2 answers
13k views

Calculating Fragmentation offset doubt

Suppose we have a data of 4500 bytes which passes through 2 routers of MTU 2600 and 1400 respectively. What will be the resulting fragments at the 2nd router (1400 MTU one)? The 4 fragments at 2nd ...
Zephyr's user avatar
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1 vote
2 answers
2k views

Clear df-bit of incoming packets

How I can clear DF bit from incoming packets on Juniper SRX? As example, on Cisco router it can be done by route-map on ingress interface: route-map clear-df-bit permit 10 match ip address 111 ...
Andrey Prokhorov's user avatar
2 votes
2 answers
2k views

When do IP packets get reassembled if fragmentation occurs in a tunnel?

I've read that fragmented IP packets "always" become reassembled at their ultimate destination, e.g. the recipient host. (see for instance http://www.tcpipguide.com/free/t_IPMessageReassemblyProcess....
rigor's user avatar
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5 votes
2 answers
23k views

Ip fragmentation and packet headers

I read somewhere that a fragmented ip packet can further be fragmented depending on the changes in the network. Now how is the packet reassembled at the router. Because the identification bit can be ...
john 's user avatar
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1 vote
1 answer
190 views

Is Path MTU Protocol more beneficial for IPv6

Should Path MTU Discovery (PMTUD) be implemented over fragmentation regardless of whether it is IPv4 or IPv6? Or should it just be implemented in ipv6 due to fragmentation now being handled through ...
JBoH's user avatar
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1 vote
1 answer
515 views

Fragmenting a Tunnel Packet

I was going through this Cisco Documentation - Resolve IP Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPSEC I have a confusion with example 3. Screenshot below. As I understand, with the ...
LSherwell's user avatar
2 votes
1 answer
4k views

How does a Cisco ACL handle fragments

We have an ASR1000, and I have the following ACL, but yesterday someone hit us with big DDoS attack, and I found it was a DNS amplification attack. so all source port for 53, and it was definitely a ...
Satish's user avatar
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2 votes
2 answers
3k views

IPv4 fragmentation - overlapping fragments

When are overlapping fragments created and why? Is there any legitimate scenario in which they are used or are they just used by attackers, like in the teardrop attack? And how is receiver suppose to ...
9cvele3's user avatar
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1 vote
1 answer
848 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 ...
pabloBar's user avatar
1 vote
2 answers
4k views

ICMP Fragmentation

Would a ping (echo request) to a reachable IP address with a size of 65500 bytes, end-to-end path MTU of 1500 Bytes, and the DF flag not set, work by having the peer responding an ICMP? 21:05:31....
Dense.mode's user avatar
1 vote
1 answer
2k 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?
Rakesh Nittur's user avatar
7 votes
1 answer
303 views

How are ping times computed

I have been graphing ping (IPV4) responses times/vs packet size. I was expecting to see a discontinuity of around 2*MTU/BandWidth in response time around the MTU boundary (actually, around 1464 byte, ...
Alien Life Form's user avatar
2 votes
1 answer
415 views

cisco ACL no counter

We have few access-list and all showing counter for hit but one access list not showing anything. C3850#show access-lists 101 Extended IP access list 101 5 permit ip 101.142.61.0 0.0.0.255 any (7 ...
Satish's user avatar
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0 votes
1 answer
348 views

Same offset in fragmented IP packets when using Covert channel

I am currently experimenting which Tunnelshell. So, I launched it on the victim and on the attacker, executed a command via the Tunnelshell and captured the traffic via Wireshark to see what's going ...
John Doe's user avatar
3 votes
2 answers
27k views

How does a router behave when some of the fragments of a packet is lost?

Consider an example where host-A is sending data to host-B. While the fragments traverses many routers in between, some of the fragments are lost. So now the router identifies this and waits for that ...
Rakesh Nittur's user avatar
3 votes
1 answer
347 views

Cisco IP Fragments ACL strange behavior

I am testing following ACL on Cisco 3850 L3 switch : C3850#show ip access-lists 101 Extended IP access list 101 10 deny ip any any fragments 20 permit ip any any (268 matches) I applied ...
Satish's user avatar
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