Subject: Re: random ip_id must be configurable
To: None <>
From: Jun-ichiro itojun Hagino <>
List: tech-net
Date: 09/16/2003 10:38:42
> Getting back to the original problem I was talking about:
> On Sat, Sep 13, 2003 at 05:04:01PM +1000, Simon Burge wrote:
> > id 52018  last call for id at    465455, current call    465456 (diff     1)
> > id 61704  last call for id at   3483418, current call   3483419 (diff     1)
> Do we have any protocol problems when using this generator in its
> current form?  One case I'm specifically wondering about is in
> libc/net/res_mkquery.c.
>   dns client sends request #1 with id N for host
>   dns client sends request #2 with same id N for host
>   server replies to request #2 with result
>   server replies to request #1 with result
> Is there anything in the dns client code that would detect that the
> replies were sent in reverse order, or will the application assume that
> because the ID matches that everything is ok?
> Maybe we should #ifdef out the use of the current generator until this
> problem is addressed?

	with which revision did you perform the test?  if possible put the
	test code to src/regress?  btw, by calling randomid() too frequently
	didn't you put arc4random() into entropy starvation?

	if dns clients are different process, they would use the different UDP
	source port for #1 and #2, so there's no problem.
	otherwise, res_send() checks if the question section of query matches
	the reply, so there's no big confusion (id check happens beforehand,
	so that could affect the end result).