Re: [lwip-users] pinging

[Jonathan Larmour]

Marcin Prusinski wrote:
> Thanks for the reply,
> I have one more question about this checksum. In ICMP ECHO header -
> there are those fields:
> type - 8 bits
> code - 8 bits
> checksum - 16 bits
> id 16 bits
> and seq number 16 bits
> in exactly this order. Which fields are being computed in checksum ?

The whole IP header. You set the checksum field itself to 0 when working 
it out.

> Should I use /inet_chksum/ like that:
> /inet_chksum(iecho,1)/ ?  - where iecho is pointer to icmp_echo_hdr .
> Then what's the point of 16 bit chksum field for 16 bit of data ?

http://www.tcpipguide.com/free/t_IPDatagramGeneralFormat.htm

Try something like:

#include "lwip/icmp.h"

{
  struct icmp_echo_hdr ping_pkt;
  static u16_t icmp_seq;
  u16t chksum;

  ping_pkt._type_code = ICMP_ECHO;
  ping_pkt.chksum = 0;
  ping_pkt.id = 0x8765;
  ping_pkt.seqno = icmp_seq++;
  chksum = inet_chksum( &ping_pkt, sizeof(ping_pkt);
  ping_pkt.chksum = chksum;


And then you can send ping_pkt down the raw socket you should have created 
with netconn_new_with_proto_and_callback(NETCONN_RAW, IP_PROTO_ICMP, 
NULL); or whatever is appropriate to the API you are using.

At least that's what I think... I haven't tried the above, so it may not 
be quite right.

Jifl
--
eCosCentric    http://www.eCosCentric.com/    The eCos and RedBoot experts
Company legal info, address and number:   http://www.ecoscentric.com/legal
------["The best things in life aren't things."]------      Opinions==mine