[BusyBox] dhcpc: broadcast flag

Doug Kehn rdkehn at yahoo.com
Fri Dec 10 11:53:42 UTC 2004


Try using a hub.  Connect the device running udhcp and
the packet sniffer to the hub.  And then connect the
hub to the switch.  Packet sniffing is much easier
through a hub than through a switch.

...doug

--- Brenda Butler wrote:

>  
> Sorry for the delay in updates, we had a few fires
> to fight.
> 
> It turns out the new busybox does not fix the
> problem.
> Neither does setting the broadcast bit in the DHCP
> packet, 
> nor setting the hardware type to 6 (instead of the
> default 
> 1), nor doing all these things at once.
> 
> Now the principal investigator has seen what I have
> seen, 
> that is that although udhcp reports on the console
> that it is 
> sending DISCOVER packets, only the 5th or 6th one
> actually 
> shows up on the network.  He used to say that all
> the packets 
> went out, but the managed switch wasn't responding
> due to the 
> spanning tree algorithm back-off timeouts, and/or
> the packets 
> were corrupted.  I think that was when ARMmon was
> doing the 
> networking, rather than when busybox was doing it.
> 
> I forgot to answer the question "is udhcp in busybox
> 
> 1.00-pre3 the same version as the one in
> busybox-1.00" in my 
> last reply.  The answer is yes, it is the same as
> far as I can tell.
> 
> About the link negotiation, we're having trouble
> with that... 
> We still don't know why.  But I wouldn't have
> thought that 
> would cause problems with the DISCOVER packets, they
> don't go 
> out till the link negotiation is done with (whatever
> it turns 
> out to come to).
> 
> Oh well.
> 
> cheerio,
> bjb           bbutler at symbium.com 
> 
> > -----Original Message-----
> > From: Brenda Butler 
> > Sent: Friday, November 26, 2004 2:25 PM
> > To: busybox at mail.codepoet.org
> > Subject: Re: [BusyBox] dhcpc: broadcast flag
> > 
> > 
> > 
> > Thanks for the long response and references to
> standards,
> > much appreciated.
> > 
> > We haven't even tried any busybox changes yet, the
> > latest theory is that the Dell switch on which we
> > see these problems is misconfigured to use
> spanning
> > tree on end-points like our device (as opposed to
> > other managed switches).
> > 
> > I'll keep you-all posted.
> > 
> > I'm having the principal investigator try out
> busybox
> > 1.00 anyway :-)  I just now made up a rootfs with
> it and
> > delivered it to him.
> > 
> > 
> > 
> > On Fri, Nov 26, 2004 at 08:31:38AM -0800, Doug
> Kehn wrote:
> > > --- Brenda Butler wrote:
> > > > 
> > > > 
> > > > We've been having some flaky networking
> happening.
> > > > 
> > > > We are using Busybox 1.00-pre3 but I see the
> code
> > > > for
> > > > creating the DISCOVER packets (init_header) is
> > > > pretty
> > > > much the same for busybox 1.00.
> > > > 
> > > 
> > > Does BusyBox 1.00-pre3 also include udhcp
> 0.9.9-pre or
> > > an earlier udhcp version?
> > > 
> > > > The flaky networking consists of:
> > > > 
> > > > software sends out DHCP DISCOVER
> > > >    - sometimes it doesn't get to the network
> > > > (observed
> > > >         from another machine on hub)
> > > 
> > > Is the interface up?  If you are not seeing any
> > > DISCOVER packets a quick ifconfig check will
> tell you
> > > if the interface is up.  Also is udhcp outputing
> > > 'Sending discover...'?
> > > 
> > > >    - sometimes it gets to the network
> (observed from
> > > >         another machine on hub) and isn't
> answered
> > > >         until the 5th or 6th or later try
> > > 
> > > I would check the sever logs to see why it isn't
> > > replying.
> > > 
> > > >    - sometimes it gets to the server and a
> reply
> > > > (DHCPOFFER)
> > > >         is sent first try, and networking
> proceeds
> > > > normally.
> > > > 
> > > 
> > > I take it that nothing has changed.  For some
> reason
> > > it just decided to work?
> > > 
> > > > 
> > > > Usually when it fails, it consistently fails. 
> But
> > > > another
> > > > card in the same slot (same environment) will
> > > > succeed.
> > > > The same card in other environment usually
> succeeds.
> > > > But same card back in same slot still fails.
> > > > 
> > > > The suggestions we've had so far are:
> > > > 
> > > > - make sure the broadcast bit is set
> > > 
> > > The broadcast bit tells the _server_ to
> broadcast
> > > replies back to the client.  This isn't the
> problem
> > > because, as you said above, dhcp does work (just
> not
> > > consistently).
> > > 
> > > > - Set the htype field in the dhcp packet to 6
> > > > (ARPHRD_IEEE802)
> > > 
> > > Hm.  Are you running an 802 (i.e. 802.3 frames)
> > > network or an Ethernet (i.e. Ethernet frames)
> network?
> > >  I would leave this field alone.
> > > 
> > > > - Make sure the xid field is really random (it
> seems
> > > > to be 0 always)
> > > 
> > > Make sure you are looking at the correct field. 
> The
> > > field before (hops) and after (seconds elapsed)
> the
> > > xid field are 0.  I never observe and xid = 0.
> > > 
> > > > 
> > > > I'm looking for comments, advice and stories
> of
> > > > similar cases,
> > > > thanks!  Advice of the sort "upgrade to
> busybox
> > > > 1.00" would have
> > > > to be accompanied with specific info about
> what
> > > > changed, as
> > > 
> > > In the future I'd be less demanding.  You'll get
> more
> > > responses.  So what if someone only says
> "upgrade to
> > > busybox 1.00".  Someone else might be more
> helpful.
> > > 
> > > > I don't see that these specific fields are any
> > > > different in
> > > > 1.00 from 1.00-pre3.  I'd love to have an
> excuse to
> > > > force
> > > > the upgrade now, so if I missed something
> please do
> > > > let me
> > > > know.
> > > > 
> > > 
> > > Why not just try it out?  Just because you try
> it out
> > > doesn't mean you have to upgrade.
> > > 
> > > > I'll be trying out the above suggestions but
> I'm
> > > > interested in
> > > > any gotchas that you'd know about.  I really
> know
> > > > nothing
> > > > about the htype field...  
> > > > 
> > > 
> > > IMHO the above suggestions won't do any good.
> > > 
> > > Please read RFC2131, RFC2132, and
> > > http://www.iana.org/assignments/arp-parameters.
> > > 
> > > > It is being suggested to change that from 1 to
> 6
> > > > because the
> > > > link negotiation is being held at 10 MB
> (rather than
> > > > going to
> > > > 100 MB where it should be) and someone noticed
> that
> > > > field is
> > > > called 10MB.  Personally, I would have thought
> that
> > > > link
> > > > negotiation would have been done by the time
> dhcp
> > > > starts,
> > > > but I'm a newb.
> > > > 
> > > 
> > > No.  Use htype = 1 if the network is Ethernet. 
> Don't
> > > worry about the rate.
> > > 
> > > Regards,
> > > ...doug
> > > 
> > > 
> > >
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> > 
> > ---end quoted text---
> > 
> 
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> 



		
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