Re: [lwip-users] LwIP Version 1.1.1 Ping Sequence Number Errors

[Kieran Mansley]

On Tue, 2006-07-04 at 10:28 +0100, Lee Trueman wrote:
> 
>  Right I've a problem with Lwip things same to stop working after
> receiving certain packets.......... after looking into the issue I
> found that even ping was erroring...... further investigation shows
> that the ping sequence numbers are becoming invalid I.e the stack
> responds to the ICMP request but with the wrong sequence number thus
> ping just timeouts the request.......
> 
> Can someone shed some light on why this is happening ????? please see
> attached ethernet packet capture........
>  

Just to check that I've understood your problem (other than a keyboard
with "." key set to auto-repeat!) the ICMP sequence number in the ICMP
echo reply is not the same as the sequence number in the echo request?

I've had a look at the IPv4 code in the relatively recent check out I
have (not top of CVS tree, so something may have changed recently, but
unlikely) and src/core/ipv4/icmp.c is not making any change to (or
indeed even looking at) the sequence number, so this isn't an obvious
error.  

I suggest if possible you try watching the sequence number value as it
progresses through the stack with a debugger or suitable print
statements to see where it is modified.  The fact that the replies have
the correct checksum suggests it is happening before the checksum is
calculated.

Your email implies that this problem affects traffic other than ICMP
too, but working out why ping is failing is probably a good start.

Is it a problem that has started recently or has it always been there as
far as you know?

Hope that helps.

Kieran