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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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1answer
35 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 ...
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2answers
145 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 ...
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1answer
432 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 ...
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2answers
73 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, ...
2
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1answer
287 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 ...
2
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2answers
165 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 ...
4
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1answer
230 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
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1answer
526 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 ...
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2answers
8k 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 ...
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2answers
573 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 ...
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vote
2answers
966 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....
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2answers
17k 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 ...
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1answer
127 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 ...
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1answer
259 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 ...
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1answer
1k 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 ...
2
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2answers
1k 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 ...
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1answer
375 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
2k 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....
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1answer
952 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?
2
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1answer
191 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 ...
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1answer
147 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 ...
2
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1answer
1k 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 ...
5
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2answers
2k views

Why does IKE use UDP instead of TCP?

Why does IKE use UDP, and handle any retransmission itself? (Larger IKE packets may cause UDP fragmentation and are dropped by some ISPs: IKE over TCP.
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1answer
779 views

IP Datagram Fragmentation total length and payload calculations

I do not understand how to fragment a IP datagram. Let's say the original datagram has a total size of 302 (20bytes header and 282 bytes payload). My datagram needs to be fragmented since it goes ...
2
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2answers
467 views

IP Fragmentation

When Device A sends an IP datagram toward Device B, the IP Layer of Device A computes if it must or not fragment the IP datagram to fit the link MTU. Sent to the next hop, the process will be repeated....