Low Bandwidth on intercontinental connections

[Adrian Chadd]

Hi Marc,

You definitely have enough information now for a PR. Would you please
file all of this into a PR so one of the IP stack people can take a
look?

Thanks,


Adrian


On 22 November 2012 07:42, Marc Peters <marc at mpeters.org> wrote:
> On 11/22/2012 02:20 PM, Ingo Flaschberger wrote:
>> Am 22.11.2012 13:38, schrieb Marc Peters:
>>> interesting, the MTU is way lower, than i expected. Through the VPN
>>> tunnel, only 1322 bytes are possible without fragmentation. ScreenOS
>>> adds 42 additional bytes per paket and the FreeBSD box is receiving
>>> 1364 bytes, according to tcpdump. From the outside (only one Netscreen
>>> on the way), 1472 is the maximum possible size to send pakets without
>>> fragmentation (-D). Which MTU would you suggest to use? Shouldn't the
>>> MTU discovery of FreeBSD handle this correct?
>>
>> do you see fragmented tcp packets on the receiving site in tcpdump?
>
> nearly every packet is fragmented, if i read th [TCP segment of a
> reassembled PDU] correct. Those have a length of 1364. Thera are also
> lots of [TCP Window Update] (every two to three acks from the receiving
> host, where the tcpdump took place). After some time, there were lots of
> [TCP Dup ACK] from the receiving host and the throughput went to a crawl
> and had lots of retransmissions. After 30 sec. everything went back to
> "normal" as of transmitting pakets without dubs and retransmissions.
>
> The same tcpdump collect on the Linux hosts, the packets had a length of
> 1514 and no dubs or retransmissions.
>
> I didn't get the option JUMBO_MTU removed, but removing TSO4 didn't
> changed anything.
>
> Adding packetfiltering and the pipe didn't change anything, too.
>
>>
>> When you load the tcpdump data (tcpdump -s 1500 -w filename ...) into
>> wireshark, you can graph the speed (bit/sec, packets/sec) and do some
>> more tcp analysis.
>>
>> Kind regards,
>>     Ingo Flaschberger
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