[BusyBox] dhcpc: broadcast flag

[Doug Kehn]

--- 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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