Actually fragmentation is a layer 3 issue. IP packets encapsulate both UDP
and TCP and it is the IP datagram that can get fragmented. Thats why they
have the fragmentation offset and identification fields in the IP header;
to take care of the fragmented packets.
TCP sequence numbers add a touch of reiliability to the TCP protocol by
ensuring that the TCP segments are arrived in order. However, UDP is not
reliable as it does not have any sequence numbers so if UDP segments do come
out of order it is the responsibility of a higher layer to point that out.
In short i think you are getting confused between segmentation and
fragmentation. Segmentation occurs at layer 4 while fragmentation occurs at
layer 3. IP handles all the fragmentation issues so be it TCP or UDP
encapsulated in IP fragmentation doesnt care for that matter.
Hope this clears things up.
Regards
Atif
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
PORTER Tara
Sent: Wednesday, August 30, 2000 1:29 PM
To: [EMAIL PROTECTED]
Subject: UDP and Fragmentation
Hello everybody,
I am in the process of studying for my CCIE written and I came across a
question that I can not find an answer to. It is about UDP
and fragmentation. What happens when UDP packets are fragmented? Do the
packets have a sequence number in thier header and does
each segment have a header?
If anybody has an idea of where I can find the anser to that question, it
would be really appreciated. I've checked the Cisco CD
and numerous books that I have, but I can't seem to find it. I know the
concept of fragmentation, ie, once a packet is fragmented
it doesn't get reassembled untill the end station. If one fragment is lost,
the whole thing must be sent again. In TCP, a packet
is fragmented and a header is put on each packet with a seq # to help the
end device. But what about for UDP? Is there any
difference?
Regards,
Tara Porter
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