Re: Fw: [lwip-users] Dropped Packets on PC receiver withlwip1.1.0Transmitter

[Paul Butler]

Kieran,

I've looked through a log file captured without using DHCP, and the problem
is present there as well.  In this case the MAC address for a few segments
is changed to 00:00:00:00:d5:06.  Interestingly, in both log files all the
incorrect MAC addresses have the same last two bytes as the correct address.

Regards,
Paul

Development Engineer
Vtech Engineering Corporation
978-974-9944

----- Original Message ----- 
From: "Paul Butler" <address@hidden>
To: "Mailing list for lwIP users" <address@hidden>
Sent: March 29, 2007 1:02 PM
Subject: Re: Fw: [lwip-users] Dropped Packets on PC receiver
withlwip1.1.0Transmitter


> Kieran,
>
> I've had it pointed out to me this morning that the ignored packets in the
> log file I sent you have the wrong MAC address!  You can confirm this by
> looking at segments 49 and 50: note that although the destination IP is
> still 192.168.16.36 (which is correct), the MAC address changes from
> 00:06:1b:c5:d5:06 (correct) to 00:10:24:28:d5:06 (incorrect).  Presumably,
> the receiver looks at the MAC address and discards the segment.  In this
> case, the transmitter retransmits at segment 55 using the correct MAC
> address and the system recovers.  Later in the same file, segments 133 and
> 134 are sent to the same incorrect MAC address, but the retransmissions at
> segments 151, 153, 155, and 157 are sent to a new incorrect MAC address
> (00:11:43:ea:d5:06).  This explains several of the symptoms I have been
> seeing.
>
> Can you think of a reason the destination MAC address would be getting
> corrupted?   There are ARP segments in the logfile, and presumably more
> before I started capturing, but none immediately preceding the corrupted
> packets.  Given that several identical segments are sent, I have a hard
time
> believing this is introduced on the wire.
>
> Regards,
> Paul
>
> ----- Original Message ----- 
> From: "Kieran Mansley" <address@hidden>
> To: <address@hidden>
> Sent: March 29, 2007 10:22 AM
> Subject: Re: Fw: [lwip-users] Dropped Packets on PC receiver with
> lwip1.1.0Transmitter
>
>
> > On Thu, 2007-03-29 at 11:00 -0500, Paul Butler wrote:
> >
> > > I've attached the complete log in wireshark (ethereal) pcap format,
> please
> > > let me know if you see anything interesting.  If you think can get it
to
> > > post to the list and get some more eyes on it, I'd appreciate it.
> >
> > I've had a quick look and can't see anything wrong with the packets that
> > are getting ignored.
> >
> > However, if Window's thought they had a bad checksum, it would not send
> > an ACK as it wouldn't trust the packet enough to work out where to send
> > the ACK to.  However ethereal things these packets checksum OK, and
> > given that you've captured this at the Window's end of the connection,
> > the scope for it going wrong from this point is small.
> >
> > If you were using linux at this point I'd suggest looking at the network
> > stack statistics using "netstat -s" while these packets are coming in -
> > it should tell you why it is rejecting them.  I'm not sure how to
> > achieve something similar on windows, but I guess it probably does keep
> > track of how many packets were dropped due to bad checksums etc, and you
> > could watch those counters to find out why it's dropping them.
> >
> > Kieran
> >
> >
> >
> > _______________________________________________
> > lwip-users mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/lwip-users
> >
>
>
>
>
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