Re: Fw: [lwip-users] Dropped Packets on PC receiver with lwip1.1.0Transmitter

[Paul Butler]

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
>