Wireshark · Ethereal-dev: Re: [Ethereal-dev] where is the field of Urgent Pointer in TCP

[Jason House <jhouse@xxxxxxxxx>]

> From: Guy Harris <guy@xxxxxxxxxxxx>
> On Tuesday, July 22, 2003, at 6:00 PM, li wrote:
>
> > when decode packet to TreeView, after show TCP checksum, where is the 
> > last two bytes of Urgent Pointer;
>
> Nowhere, unless the URG bit is set in the TCP header.  We only put it 
> into the protocol tree if URG is set.  (If URG isn't set, the packet 
> isn't setting the urgent pointer, and the urgent pointer field's value 
> is ignored.)


  If my understanding is correct, it isn't that the urgent pointer 
"isn't set", but is actually set to 0.  If this is correct, should TCP 
possibly display non-zero urgent pointers if the URG bit is not set?  Am 
I mistaken about all TCP implementations setting the urgent pointer to 0?
  Especially with an invalid CRC, I imagine that such functionality 
might be useful.