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Wireshark-users: Re: [Wireshark-users] Fwd: sequence number and packet id

From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Sat, 12 Apr 2008 14:36:02 -0700
Fabiana moreno wrote:
Thank you very much for your help. I have been reading about all this the whole day, it�s just confusing somehow. I just need my packets fragmented so i can have the packet id so i can do some calculations....

What are the calculations you're trying to do, and why you need a packet ID?

From what i have read the kernel version 2.6 dont fragment packets

No.

The 2.6 kernel will fragment packets if necessary.

Furthermore, even if it - or any *OTHER* IP implementation - sends an IP packet that doesn't have the "don't fragment" bit set, it can't assume that some *other* host along the route to the destination won't fragment the packet, so, regardless of whether the host sending the packet fragments it, if the packet doesn't have "don't fragment" set, it has to give the packet as close to a unique IP ID as it can.

However, if the "don't fragment" bit is set, it doesn't have to give the packet a unique IP ID - and at least some versions of the Linux kernel, and possibly some versions of some other kernels, don't give those packets unique IP ID's.