Re: [lwip-users] auto ip is a valid address?

[vincent cui]

Yes,. It is. 
Thank you

Vincent  

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of RAc
Sent: 2013年1月21日 PM 8:39
To: address@hidden
Subject: Re: [lwip-users] auto ip is a valid address?

What do you mean DHCP Server? There is no DHCP server running on your lwip
machine; you probably refer to a Web Server running on your unit?

When your DHCP query fails, Auto IP is applied but DHCP is periodically
reinvoked, so as soon as the DHCP server is available, your unit will obtain
a proper IP address valid in your net.

I suspect that you run into a very typical trap: You try to access a Web (or
other application) server that is a moving target due to being a DHCP client
and you don't like it when the address changes because then your previous
address isn't valid anymore.

The simple answer is: Don't. Do NOT assume that a dynmaic address is a valid
target for a communication. It's only going to cause you headaches. There is
no easy solution out; you will need some kind of high level protocol such as
DynDNS or SIP to map changing addresses to abstract addresses such as DNS
addresses. Even then, it's not guaranteed to work properly. These things are
extremly tricky.

Your safest bet is to require that your unit runs in an environment where
the DHCP server guarantees a constant DHCP address for your MAC address.

And no, don't call dhcp_close. If you wish to force dhcp renegotiation, use
setiflinkup() (or something along those lines; I don't have the code in
front of me right now). That'll reinvoke dhcp. But normally all of that
works automatic.




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