Can someone verify that the setup does, in fact, support the RFC?
I.e. - use hping or other packet crafting tool to generate a big (say,
4K) TCP packet with the "don't fragment" flag set, and see (with
tcpdump, or a real sniffer, such as ethereal) whether a "fragment
needed" ICMP is sent.
If it is not sent, but the packet does not go through, then there is a
real problem. I would try, at this stage, incrementing the TTL, starting
from one, and seeing where the "ICMP time exceeded" messages stop
arrive. Wherever that happens - that's the curlpit (or the one before).
hping2 can be D/L from http://www.kyuzz.org/antirez/software.html
The command line for a single, established, ~ 4KB packet to host foo,
with the "don't fragment" flag set is
hping2 foo -c 1 -A -d 4096 --dontfrag
hping will display any reply packets received. If you want to test the
TTL as well, add --ttl # to the arguments.
Shachar
Cedar Cox wrote:
> On Tue, 12 Jun 2001, Miki Shapiro wrote:
>
>> My opinion however remains that it is completely unneccesary to lower MTU
>> on all your windows clients and the linux ether interface, for the
>> benefit of time that you buy - the extra time that it takes your linux
>> router to get a too-large chunk, digest it, send a single ICMP packet
>> back, and your winsock to digest that (what? 20 extra miliseconds at the
>> start of a TCP session? these two packets have to traverse a single
>> ethernet wire... That's completely negligible).
>>
>> Is there anyone on this list for whom specifically this technique actually
>> *solved* the broken sessions problem (as opposed to optimizing sessions by
>> 20ms on the first packet?) ? If so, by accomplishing *what*?
>>
>> .. If not, maybe it's not worth bothering people with in the HowTo...
>
>
> Me, for one. Without a MaxMTU I typically never got a response beyond 4
> packets, ie. things just did not work. With MaxMTU 1452, everything seems
> to be just about normal (that is to say I haven't seen any problems yet).
>
> -Cedar
>
>
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