Im having problems with Opera browser with loading certain sites.

While sniffing with Ethereal, I get a very very high count of "TCP Dup
ACK" (and I mean a VERY HIGH count, the loading of Slashdot have more
than 45k of it).

Im pasting two lines of the log, if anyone can explain whats happening
Im very grateful. (I cant paste the entire log here, its VERY long. But
i can compress and upload it somewhere)

46488 161.837312 10.0.0.2 66.35.250.55 TCP
[TCP Dup ACK 258#23057] 1209 > http [ACK] Seq=1313 Ack=3837 Win=32464
Len=0
46489 161.843931 66.35.250.55 10.0.0.2 TCP
[TCP Dup ACK 299#23047] http > 1209 [ACK] Seq=1662 Ack=1312 Win=16384
Len=0

ps. I received DupAcks for about 3 minutes with non-stop bandwidth of
8kb/s
ps2. That happens in Linux also, but the log was captured in Windows
ps3. It only happens with Opera.. Firefox and IE is everything ok
ps4. Im not behind a firewall or something. My router is fully open to
internet access

Thanks in advance,
Hugo

hugopessotti@yahoo.com.br wrote:
> Im having problems with Opera browser with loading certain sites.
>
> While sniffing with Ethereal, I get a very very high count of "TCP Dup
> ACK" (and I mean a VERY HIGH count, the loading of Slashdot have more
> than 45k of it).

DupACKs indicate that the sending (of the dupACK) system (your desktop,
I presume) has noticed a gap in the TCP sequence from the sender.
Packets have either been lost or misordered.

This is a normal thing to expect when the internet is in your way,
especially with a protocol like HTTP where you tend to be transferring
large amounts of readily availble data. ...As opposed to, say, telnet.

45,000 dupACKs when you load slashdot's front page? I just loaded it
and only saw 282 packets of any type. You sure about this?

> Im pasting two lines of the log, if anyone can explain whats happening
> Im very grateful. (I cant paste the entire log here, its VERY long. But
> i can compress and upload it somewhere)
>
> 46488 161.837312 10.0.0.2 66.35.250.55 TCP
> [TCP Dup ACK 258#23057] 1209 > http [ACK] Seq=1313 Ack=3837 Win=32464
> Len=0
> 46489 161.843931 66.35.250.55 10.0.0.2 TCP
> [TCP Dup ACK 299#23047] http > 1209 [ACK] Seq=1662 Ack=1312 Win=16384
> Len=0

So, 10.0.0.2 is complaining to 66.35.250.55 about missing or misordered
packets.

> ps. I received DupAcks for about 3 minutes with non-stop bandwidth of
> 8kb/s

Do you mean "3 minutes, then it cleared up" or "for the whole 3 minutes
I tested" ?

Is the stated bandwidth less than you think it should have been?

> ps2. That happens in Linux also, but the log was captured in Windows

Same box or different boxes?

> ps3. It only happens with Opera.. Firefox and IE is everything ok

Doesn't make sense. All applications use the same TCP, and presumably
the same ISP.

> ps4. Im not behind a firewall or something. My router is fully open to
> internet access

You must be behind something if your address is 10.0.0.2

Hugo, is there actually a problem here? I have the sense that you're
disappointed with your downstream bandwidth, but you haven't explicitly
stated so...

I think the problem you're experiencing has to do with the way Opera
renders the page. Your downloads are probably equally bad (or good)
regardless of the browser, but Opera is waiting for some last bit
before loading the page the IE doesn't bother to wait for.

....That's not to say that you don't have a packet loss problem, but it
can explain the difference you experience with the various browsers.

/chris

hugopessotti@yahoo.com.br wrote:
> Im having problems with Opera browser with loading certain sites.
>
> While sniffing with Ethereal, I get a very very high count of "TCP Dup
> ACK" (and I mean a VERY HIGH count, the loading of Slashdot have more
> than 45k of it).
>
> Im pasting two lines of the log, if anyone can explain whats happening
> Im very grateful. (I cant paste the entire log here, its VERY long. But
> i can compress and upload it somewhere)
>
> 46488 161.837312 10.0.0.2 66.35.250.55 TCP
> [TCP Dup ACK 258#23057] 1209 > http [ACK] Seq=1313 Ack=3837 Win=32464
> Len=0
> 46489 161.843931 66.35.250.55 10.0.0.2 TCP
> [TCP Dup ACK 299#23047] http > 1209 [ACK] Seq=1662 Ack=1312 Win=16384
> Len=0
>
> ps. I received DupAcks for about 3 minutes with non-stop bandwidth of
> 8kb/s
> ps2. That happens in Linux also, but the log was captured in Windows
> ps3. It only happens with Opera.. Firefox and IE is everything ok
> ps4. Im not behind a firewall or something. My router is fully open to
> internet access
>
> Thanks in advance,
> Hugo
>

It happens to me too, on Linux using Firefox. Slashdot does it
quite often. I haven't timed how long it goes on for, but 3
minutes sounds about right. I get the impression that I get more
than 8Kb/s of it though. I guess the throughput is quite
sensitive to round trip time.

It seems odd that one would receive many duplicate ACKs from a sender.
Perhaps the receiving stacks in question are mistakenly interpreting
the ACK field in the arriving data segments as duplicate ACKs? Does a
packet trace show actual standalone (no data in the segment) ACKs
arriving from the source?

rick jones
--
Process shall set you free from the need for rational thought.
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...