[lwip-users] IP packets getting dropped

[Robert Schilling]

Hi Guys,

I'm trying to port lwIP 1.3.2 to a NXP LPC1768. I'm using CoOS 
(www.coocox.com) as my rtos.
ARP is working fine. If I ping my device I get an ARP respond. But ICMP 
requests don't get a reply.

I found out that all IP packets getting dropped.

  if ((iphdr_hlen > p->len) || (iphdr_len > p->tot_len)) {
    if (iphdr_hlen > p->len)
    LWIP_DEBUGF(IP_DEBUG | 2, ("IP header (len %"U16_F") does not fit 
in first pbuf (len %"U16_F"), IP packet dropped.\n",
                               iphdr_hlen, p->len));
    if (iphdr_len > p->tot_len)
    LWIP_DEBUGF(IP_DEBUG | 2, ("IP (len %"U16_F") is longer than pbuf 
(len %"U16_F"), "
                               "IP packet dropped.\n",
                               iphdr_len, p->tot_len));
    /* free (drop) packet pbufs */
    pbuf_free(p);
    IP_STATS_INC(ip.lenerr);
    IP_STATS_INC(ip.drop);
    snmp_inc_ipindiscards();
    printf("Buffer Error\n");
    return ERR_OK;
  }

This code snippet is out of ip.c at line 250. The if condition 
(iphdr_len > p->tot_len) is true and so the packet gets dropped.
The IP packet is corect. Checked with Wireshark. The IP-Header length is 
20 byte and IP-data is 40 byte
(correct for ICMP-Pig Request). But p->tot_len is always 58 or 59 in 
order to be greater than 60 byte (whole IP packet).

I hope someone could help me.

Thanks in advance!
Best regards from Austria
Robert