Host A sends a 1400 byte IP packet to Host B over an Ethernet and PPP link. The PPP link has an MTU of 532 bytes, which means that the IP packet will be fragmented into 3 smaller packets.
Fragment 1 is received first. It has a unique ident and the M bit flag is set, indicating there are more fragments to come. However, fragment 3 is received next, due to some re-ordering in the network. This fragment has the same ident as fragment 1, but the M bit is not set, because it's the last fragment. Fragment 2 is received shortly after.
What will the receiving host do?
- Will the receiving host know that the offset and packet length do not match up, and assume an intermediate packet has been either dropped or re-ordered in the network, and wait for it?
- Will the receiving host reassemble the packet (both the header checksums match) and pass it to the higher layer (where it will fail an IP checkum over the data if using UDP/TCP). Jaimao discografia completa download.
- Will the receiving host drop all fragments for this ident.
user376151
1 Answer
The receiving host knows that there are lost fragments and waits until a reassembly timeout expires. Unless the lost fragments arrive, the fragments are dropped.
RFC 791 in section 3.2 defines that :
If the timer runs out, the all reassembly resources for this buffer identifier are released. The initial setting of the timer is a lower bound on the reassembly waiting time. This is because the waiting time will be increased if the Time to Live in the arriving fragment is greater than the current timer value but will not be decreased if it is less. The maximum this timer value could reach is the maximum time to live (approximately 4.25 minutes). The current recommendation for the initial timer setting is 15 seconds.
This reassembly timeout for IPv4 and IPv6 on Linux is 30 seconds and for Windows (Vista, 2008, 7 and 2008 R2) is 60 seconds according to section 4.5 of RFC 2460:
If insufficient fragments are received to complete reassembly of a packet within 60 seconds of the reception of the first-arriving fragment of that packet, reassembly of that packet must be abandoned and all the fragments that have been received for that packet must be discarded.
jcbermujcbermu
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How to reassemble a set of UDP packets to a file sent, in my case it is an image? How to extract data and save as an image? What is some packets was damaged?
J.OlufsenJ.Olufsen5,5593333 gold badges9696 silver badges155155 bronze badges
1 Answer
- Right-click on one of the UDP packets and select Follow UDP Stream
- In the stream content dialog use Save As. to save the raw payload data for the stream
- You may need to use a binary file editor to remove extra data (eg data sent in the opposite direction or signalling messages) - alternatively, filter these out before step 1 and save in a seperate file
- If you have missing payload data you will need to repair the image somehow. There are lots of apps available that will do this for standard image formats
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I've written 2 server programs to read multiple client messages and send them back using sockets via UDP; the 2 server programs differ from the management of the receiving and sending messages back; the first one simply takes the message and sends it back, the second one receives the message and creates another process to send the message back. The client sends 10000 messages to the server and I noticed that the first one resends more messages than the second one, a lot more, like 100:1;
Here's the code for the server with only one process:
Yamaha pss-140 portasound keyboard opiniones 2. And here the code I used in the second server, the one with 2 process, one to receive and one to send back:
Reassemble Udp Packets Multiprocess Free
The client program I used with both is this:
Thanks in advance for the help!
Reassemble Udp Packets Multiprocess 1
AskManAskMan
1 Answer
There are several things wrong. You've added the fork() in an infinite loop. I doubt this is what you want because you're not calling exit in the child and you're not reaping the children in the parent ie you are likely going to run out of file descriptors on the machine you're using.
If you want to exit the child on every received message you'll need to wait on the child or you will have a lot of zombie processes use this
in the parent so it reaps the child and you don't run out of resources. You should also check to make sure that fork actually worked to see if you ran out of resources ie if if(pid < 0) you have an error.
If you fix the code and it's still slow and you know the code is correct then I'd look at process creation time. You can pass file descriptors to the child process which is what a lot of HTTP servers do ie Apache etc, this avoids the process creation overhead. Note. process creation is very cheap, using a good benchmarking tool would likely tell you exactly where the time is going.
HarryWhat Are Udp Packets
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