Angus Lees wrote:
> before everyone gets really excited about masquerading and adsl, i
> think i've uncovered a bug in telstra's end of the adsl
> connection.. more details later, i just want to confirm some things
> first:
>
> i presume i'm right in saying that i should *NEVER* see a fragmented
> TCP packet? (cos the DF bit is set)
TCP does not require that the DF bit be set. If you are asking this in a
Linux kernel masquerading context, then I don't know. I recall something
about this in a kernel configuration file, I never followed it up.
> anyone care to give me a brief summary of how atm works? ;)
>
> all i know about atm is its connection-oriented and has really small
> (53 bytes?) packets.
That's about right. I thought that they were a few bytes larger.
> specifically, what does atm do with (as a hypothetical example) a
> packet of 1500 bytes? (my two bits of atm knowledge imply it isn't
> going to do the normal IP fragmentation)
I would assume that they get chopped into appropriately sized chunks,
sent sequentially, and stuck back together upon exiting AAL. This will
almost certainly happen below IP however. IP will most likely see the
same datagram pop out the other end that you pushed in at your end.
Another possibility is that PPP is taking care of this. Remember that
your tcpdumps are actually Ethernet dumps and are therefore showing you
individual PPP chunks (packets?).
Have you read the docs that Andrew Morton pointed out yesterday?
Are you seeing lots of tiny Ethernet packets?
What MTUs are you using?
- Raz
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