Steven A. Ridder wrote:
>
> Does anyone know if a packet is fragmented, that the specific
> values in a
> field are replicated across all headers of the fragmented
> packets, or just
> the first one?
>
> Meaning, if I have a packet that has IP Prec 5, and a router
> along the way
> has to fragment the packet, would it be so kind as to put IP
> Prec on all the
> headers?
Yes, it should. Per RFC 791, a router (or gateway as the RFC calls it)
copies the contents of the header fields from the original datagram into the
new headers of all the fragments. Of course, the following fields may
change, however:
(1) options field
(2) more fragments flag
(3) fragment offset
(4) internet header length field
(5) total length field
(6) header checksum
Also, with the options field, options may or may not be copied into each
fragment. There's a bit that the sender can set saying whether they must be
or not. But in general, all bits and bytes are copied into each fragment IP
header.
Prscilla
>
> Steve
>
>
> ""Priscilla Oppenheimer"" wrote in
> message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Mossburg, Geoff (MAN-Corporate) wrote:
> > >
> > > Thanks for clearing that up;
> >
> > No problem.
> >
> > > I don't mind being told I'm
> > > mistaken. I
> > > recently decided that the only way I'm really going to learn
> > > from this group
> > > is to take a chance on confirming what I THINK I know, and
> > > asking questions
> > > about what I DON'T know. :) A lesson in humility, to be
> sure.
> >
> > I know what you mean. I like to pretend to be an uber goddess
> of all
> things
> > tech, but to learn, I have to admit to lots of cluelessness
> in some areas.
> > It can be a bit painful, but definitely worth it! :-)
> >
> > Priscilla
> >
> > > GM
> > >
> > > -----Original Message-----
> > > From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]]
> > > Sent: Wednesday, January 08, 2003 5:35 PM
> > > To: [EMAIL PROTECTED]
> > > Subject: RE: fragmentation question [7:60643]
> > >
> > >
> > > Mossburg, Geoff (MAN-Corporate) wrote:
> > > >
> > > > Someone correct me if I'm wrong:
> > >
> > > OK, you're wrong. :-) Look it up or use a protocol analzyer.
> > >
> > > > All the "fragments" have the TCP/UDP/IP headers, or else
> they
> > > > can't be
> > > > routed to their destination.
> > >
> > > Routing to their destination just requires the IP header,
> which
> > > is in each
> > > fragment. The TCP or UDP headers are not in the fragments,
> past
> > > the first
> > > one. The IP layer at the end device puts it all back
> together
> > > and hands the
> > > packet to the TCP or UDP layer. TCP or UDP get the full
> packet
> > > and can
> > > "route" it to the correct process, based on the destination
> > > port number.
> > >
> > > > "Fragmentation" is just a way of breaking up the data
> payload
> > > > into smaller
> > >
> > > Data payload from IP's point of view.
> > >
> > > > packets, but it puts individual headers on each packet.
> > > > MTU is the total size of each packet, including the
> header.
> > >
> > > The term isn't always used that way, though.
> > >
> > > > GM
> > > >
> > > > -----Original Message-----
> > > > From: Paul Dong So [mailto:[EMAIL PROTECTED]]
> > > > Sent: Wednesday, January 08, 2003 4:19 PM
> > > > To: [EMAIL PROTECTED]
> > > > Subject: fragmentation question [7:60643]
> > > >
> > > >
> > > > Hi All,
> > > >
> > > > Please shed a light on this as I am confused.
> > > >
> > > > Fragmentation for UDP/TCP:
> > > > * Only the first fragment contains the UDP or TCP
> header, not
> > > > the
> > > > sequencial fragments?
> > > >
> > > > Fragementation for IP packets
> > > > * every fragmented packet will contains ip header?
> > > >
> > > > MTU 1500 bytes, doesn't it mean the data payload can not
> > > exceed
> > > > 1500
> > > > bytes or the whole packet size(payload+header) can not
> exceed
> > > > 1500
> > > > bytes?
> > > >
> > > > Thanks in advance
> > > >
> > > > Paul
>
>
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=60926&t=60643
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