Byte and Bit Order Dissection

I think your description of Ethernet Addressing is mistaken. In your example where the MAC address 12:34:56:78:9a:bc, you say that "12" will appear on the line first. This is not correct. The "bc" will appear first. Refer to section 3.2 of the 802.3 spec. It explicitly states the byte ordering of the Length field and the CRC are high-order byte first. So, I'm led to believe that the SA and DA are low-order byte first.

This would make sense because we know that the first bit on the wire determines multicast or unicast and that this is the LSB of the entire field...which is the last byte (not of the 1st byte).

It's incomplete in this on-line version which should be:

/* dot2ip - convert a dotted decimal string into an
* IP address
*/
uint32_t dot2ip(char *pdot)
{
uint32_t i,my_ip;

my_ip=0;
for (i=0; i
my_ip = my_ip*256+atoi(pdot);
if ((pdot = (char *) index(pdot, '.')) == NULL)
break;
++pdot;
}
return my_ip;
}

Most of the ASCII graphs inlined in this on-line version of
the article are not formatted properly.

I'm contacting LJ to correct the format. In the meanwhile
you can reference my original article here if you get
confused of the ASCII graphs:

http://www.employees.org/~hek2000/articles/endianess-v0.7.html

1. A great article;
2. I suggest you create a HOWTO in the Linux Documentation Project (www.tldp.org) so that more people can benefit from your article;
3. As I know, bit0 is the MSB in Motorola PowerPC Manual; maybe you should clarify your bit numbering explicitly;

"That is, in a big endian system the most significant bit is stored at the lowest bit address; in a little endian system, the least significant bit is stored at the lowest bit address."