[lwip-users] Re: dhcp --> auto-ip --> slow boot process

[Jakob Stoklund Olesen]

"Tamas Somogyi"
<address@hidden> writes:

> My device uses dhcp+autoip option, and I noticed that finding a suitable
> IP in a network where no DHCP server present takes more than one minute,
> mainly because lwip spends 57 secs with retrying dhcp requests
> (dhcp.c).

Tamas,

I have recently submitted two patches that deal with this and other
issues with DHCP/AutoIP.

http://savannah.nongnu.org/patch/?6721
http://savannah.nongnu.org/patch/?6725

The patches have not been accepted into CVS yet.

Perhaps you could apply them to your own code base, and see if they
solve your problem? Your feedback will be appreciated.

> The question is that this 57 secs or number of retries is required by
> some specification (RFC=?) -or- merely arbitrary numbers? 

I think it is somewhat arbitrary. The RFCs do not talk much about
DHCP/AutoIP cooperation. RFC 3927 says that AutoIP must not in any way
change to operation of the DHCP client. This means that the DCHP client
will keep looking for a DHCP server. When it finds one, the DHCP address
will override the AutoIP address.

This can be a problem when getting an AutoIP address quickly after
reboot. If the DCHP server is a bit sluggish you will first get an
AutoIP address, and then a real DHCP address a few seconds later. There
is nothing wrong with that, but your software must be able to handle it.

All your TCP connections are closed when the IP address is changed.

Regards,
/stoklund