mnxvolders:
how can i make shure that the arduino takes an unussed IP adres?
i'm sorry for the long text but my knowledge of network is verry little.
greet MNX
Assuming the client (your Arduino) knows the current time, it should know if the lease is still good. If it doesn't know the current time, then the safe thing is to just ask the DHCP server to renew the lease and handle the response you get. The server will not give out your IP until the lease expires. It doesn't know if your Arduino is still connected and it's not going to check either. It's up to your Arduino to just do the correct thing.
If the call to Ethernet.maintain() returns 0 ("Nothing happened") it means that the DHCP server (presumably the router) did not find anything wrong with your IP address - no conflict with other addresses.
If you disconnect the Arduino, then reconnect it after the lease expired, and another PC got the same address in the meantime, the router will assign a new address to the Arduino. This will happen either when you call Ethernet.begin(mac), if you just turned on the Arduino, or when you call Ethernet.maintain() if the Arduino was still running when disconnected. This time, Ethernet.maintain() will return a different code (probably 4 - rebind success). Then you'll have to call Ethernet.localIP() to get the updated address.
It also depends on setting the proper MAC address, but I assume it is properly configured.
One important question is how you check whether the cable was disconnected and reconnected, i.e. how you decide in your code that you need to call Ethernet.maintain(). If you call Ethernet.maintain() only when you get a communication error, then it is probably the case that the Arduino made some attempts at using the old, no more valid IP address.
The Arduino does not need to know the time. The lease is normally issued by length. It doesn't say "the lease expires on 3-5-2013", it says "the lease expires in 2 days".
What does it matter if it is 1 January 1970 or 5 March 2013
If you reboot the Arduino, the dhcp request will be sent and a new ip will be issued if a duplicate was issued to another device in the meantime.
yes the arduino needs to the correct thing but how does the arduino knows when to ask for a new ip. It needs to ask for a new ip when he is connected to the server. how can the arduino know when he is connected and when not? if know how to do this i think i can program the rest of my code:)
SurferTim:
Don't reboot your router every 15 minutes!
Right. Problems can always be forced, but just following the established rules and going the extra mile in your software to perform basic sanity checks to "just make sure" will eliminate most problems like the ones being discussed here.
Set the dhcp lease to a very very short time. If the network is stable, then you should not have a problem with this. Ask your IT how often the network must be restarted.
SurferTim:
The Arduino does not need to know the time. The lease is normally issued by length. It doesn't say "the lease expires on 3-5-2013", it says "the lease expires in 2 days".
What does it matter if it is 1 January 1970 or 5 March 2013
If you reboot the Arduino, the dhcp request will be sent and a new ip will be issued if a duplicate was issued to another device in the meantime.
That's correct, it is issued in minutes I believe, but I'm not sure. While the client doesn't need to know the calender date/time, it does need to accurately know how long it has been since the lease was granted. Maybe it's a matter of semantics, but the client does need to know the time in some sense of the word.
I agree, it's a non-issue. There are no requirements (on the network side anyway) to wait any certain amount of time before renewing or obtaining a lease.
To the OP, know whether the server is available would be resolved by just attempting to access it in some way. Maybe PING is enough for you. I haven't used it yet, but I'd be willing to bet that there is a function call in the Arduino TCP/IP software to see if the cable is connected. The network card hardware certainly knows.
That is not true. Only the w5200 knows that. You can unplug the CAT5 cable from a w5100, and it doesn't have a clue!
Wow, you're kidding. Even the cheapest NE2000 compatible cards that I've seen can tell if the cable is connected. Heck, most MACs will auto-negotiate the connection. I'll have to look at that data sheet. Let's say I'm skeptical right now, but stranger things have been proven to me.
EDIT: I see that this is an all-in-one chip with a TCP/IP stack built in. The datasheet seems to indicated that the device should know if the cable is connected since it supports auto-negotiation and has a LINK STATE LED output pin. If the embedded software can't tell the caller the state of the link, then I'd say it was a bug in the embedded software.
The w5100 has a tcp/udp stack built-in, but does not have the sensor to detect the the physical state of the device. If the physical device becomes disconnected, the w5100 does not have a way to detect if the cable is disconnected.
You can file a complaint with Wiznet, but I almost guarantee they will say "get a W5200".
Ethernet.maintain() does nothing but return until the lease is half expired. If the dhcp lease was 2 days, then for the first 24 hours, Ethernet.maintain() returns "no action taken".
I don't know how else i can doe this. it is like in the example code
Not exactly the best choice, but it may work. The mac address is a unique identifier for network devices, and by using the example configuration you can be sure that many other devices will use it. However, most other devices in your network will use their true, unique mac address, so you can get along with it... until some of your colleagues connect their Arduinos using the sample configuration.
Look if you can find the mac address printed somewhere on the shield or the box. At the moment, however, this doesn't seem to be a problem.
mnxvolders:
i use the Ethernet.maintain(); in the begin of my void loop()
Not a perfect solution (but it seems there are none, apart from resetting the Arduino), but that would reduce the risk of reusing an invalid address. Just remember to check whether the function really returns 0 and use Ethernet.localIP() if it doesn't.
i got a standaard ethernet shield with the W5100.
So i need an other shield with the W5200 to detect the cable?
The main difference is that the W5200 has a status register that keeps track of the link state (whether the cable is attached or not). But this also requires a different version of the Ethernet library, specific for the W5200. I don't know the status of this library, whether it's complete and provides the required functionality (you can always inspect the status register within your code, but a library should give you something more, such as interrupts when the link is down).
I will change that when i know how to get always a good ip and detecting when my cable is connected:)
Do you know how i can change the lease time in my arduino.
On my desktop is is 4h, on my labtop is 1h (cmd -> ipconfig/all)
with arduino it is about half houre. (waited that long)
And it is not possible with de ethernetshield based on th W5100 to detect if there is a physical connection?
i think there is becaus when i connect my cable LED's start to work. and those led are connected to the W5100 if you look at the schematic of the ethernet shield.
sow i think it is possible but i don't know how. does someone know this?
second question.
when you use Ethernet.maintain();
what is de the diffrents betweem renew and rebind?
The time they check is that the same and how can i change this?
mnxvolders:
And it is not possible with de ethernetshield based on th W5100 to detect if there is a physical connection?
i think there is becaus when i connect my cable LED's start to work. and those led are connected to the W5100 if you look at the schematic of the ethernet shield.
sow i think it is possible but i don't know how. does someone know this?
You may attach something to pin 66 of the chip to see if it's down, or a light sensor to the LED. It seems is an output-only pin, not something you can inspect through a register. There may be some hidden API, but if there is one, it's well hidden.
Renew, rebind... Not sure about this, but I think not all calls to maintain() are actually sent to the DHCP server. Some (most) are resolved 'internally' by checking a timeout. So, if you just got your lease the next time you call maintain() it will simply return with a Nothing happened code.
Renew means you asked the DHCP server to keep your leased address, and the request was granted. Rebind means that your DHCP server did not accept your request OR did not respond, you went on asking for a while, addressing your requests to the same DHCP server, and finally broadcasted your request to whomever could give you an answer (possibly a different DHCP server).
You may attach something to pin 66 of the chip to see if it's down, or a light sensor to the LED. It seems is an output-only pin, not something you can inspect through a register. There may be some hidden API, but if there is one, it's well hidden.
I see it is an output pun of the w5100. that i the reason i think he can detect the connection because he needs to turn on the leds when my cable is connected. How does he know when he must turn on this led? and how can i found out with the arduino?
I also tried to send a mail to arduino support but can't find the mail adres. :s
