Hi,
thanks for the fast reply. I read on page 24:
Fragments are counted in units of 8 octets. The
fragmentation strategy is designed so than an unfragmented datagram
has all zero fragmentation information (MF = 0, fragment offset =
0). If an internet datagram is fragmented, its data portion must be
broken on 8 octet boundaries.
So, I think your statement is only true for the fragments of a fragmented
packet. Further the appendix of RFC 791 gives the following example:
APPENDIX A: Examples & Scenarios
Example 1:
This is an example of the minimal data carrying internet datagram:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver= 4 |IHL= 5 |Type of Service| Total Length = 21 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification = 111 |Flg=0| Fragment Offset = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time = 123 | Protocol = 1 | header checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| destination address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+
Example Internet Datagram
Figure 5.
Note that each tick mark represents one bit position.
This is a internet datagram in version 4 of internet protocol; the
internet header consists of five 32 bit words, and the total length of
the datagram is 21 octets. This datagram is a complete datagram (not
a fragment).
Regards,
Morten
------------------------------------------------------------------------
Morten Schläger Tel.: ++49 (030) 314-23834
Technical University Berlin Fax.: ++49 (030) 314-23818
Telecommunication Networks Group (TKN) morten@ee.TU-Berlin.DE
Sekr. FT 5-2/Einsteinufer 25
10587 Berlin, Germany
On Wed, 9 Jan 2002, David S. Miller wrote:
> From: Morten Schlaeger <morten@ee.tu-berlin.de>
> Date: Wed, 09 Jan 2002 10:18:20 +0100
>
> as far as I remember the IP RFC, the smallest IP fragment has a length
> of 21 octets
>
> Page 24 of RFC791 states that IP fragments must be a multiple
> of 8 octets in length in their data portion. This is because
> fragments are measured in units of 8 octets.
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