Re: Traceroute without s bit

[Andi Kleen <ak@suse.de>]

On Wed, Dec 06, 2000 at 04:07:38PM +0100, Olaf Kirch wrote:
> On Wed, Dec 06, 2000 at 02:09:05PM +0100, Andi Kleen wrote:
> > IP_PKTINFO does not allow to set source addresses, only destination
> > addresses. Source address depends on the boundage or the route. 
> 
> No. At least udp_sendmsg uses the spec_dst_addr field as the source
> address.  I added some code to my traceroute that lets you select the
> source address in order to verify that.

Please read the code again.

It uses spec_dst to select the possibly policy sourced route -- the
actual source address is only set from that route (either default or what
was set using ip route's from flag) or the bound address.



> However the good thing is that somewhere something seems to check that
> the requested address is indeed one attached to a local interface.

That's not actually checked, but in most simple routing configurations it is
true.


> 
> > > 	13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0
> > > 	13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0
> > > 	13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0
> > > 	13:43:02 poll([{fd=4, events=POLLERR}], 1, 5) = 0
> > 
> > POLLERR is returned until the error queue is empty. I suspect you're
> > not emptying it properly in all cases. It can contain multiple errors.
> 
> But it doesn't return POLLERR. If it was returning it, pollfd.revents
> would be set. pollfd.events is the event mask that's being passed _into_
> the poll() call.

Right. I missed your 5ms timeout @)

-Andi
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