dns lookup only works with DHCP and not with static setup (EtherCard library)

Question

When I use DHCP with ether.dhcpSetup() the DNS lookup for NTP ether.dnsLookup("0.pool.ntp.org") works fine, but when I use a static setup (because my Android app needs to know the IP address) with ether.staticSetup(myip); then this returns false and I don't get an IP address from the NTP pool. How come?

I have an Arduino Nano ATmega328 with a ENC28j60 ethernet shield, and therefore use the EtherCard libray.

Full MWE:

#include <EtherCard.h>      // https://github.com/jcw/ethercard
#include <Time.h>           // http://www.arduino.cc/playground/Code/Time

static byte mymac[] = { 0x74,0x69,0x69,0x2D,0x30,0x31 };
static byte myip[] = {192, 168, 2, 106};
const char poolNTP[] PROGMEM = "0.pool.ntp.org"; //pool to get time server from
uint8_t ntpMyPort = 123; //port for the time server, no idea why needed

byte Ethernet::buffer[700];

void setup () {
  Serial.begin(9600);

 //do not forget to add the extra '10' argument because of this ethernet shield
  if (ether.begin(sizeof Ethernet::buffer, mymac, 10) == 0) {
    Serial.println(F("Failed to access Ethernet controller"));
  }

  //static setup
  ether.staticSetup(myip);
  ether.printIp("Address: http://", ether.myip);

 //this works
//  if (!ether.dhcpSetup())
//    Serial.println(F("DHCP failed"));

  //Find ip address of a time server from the pool
  if (!ether.dnsLookup(poolNTP)) {
    Serial.println("DNS failed"); //with static setup this line is executed, not so with DHCP
  }
  ether.printIp("Lookup IP   : ", ether.hisip);
}

void loop () {}

@KIIV As John Burger suggested in his answer that's probably one mistake, but it's not solved yet even with adding dns ip as well (see comment there) — PHPirate
– PHPirate, Commented Aug 31, 2016 at 16:29
BTW: why don't you set fixed IP on your DHCP for this device? It could save you these troubles. — KIIV
– KIIV, Commented Aug 31, 2016 at 16:37
@KIIV Sounds good but what do you mean? The documentation says dhcpSetup() doesn't take any parameters, so no way to give it my ip? — PHPirate
– PHPirate, Commented Aug 31, 2016 at 16:42

John Burger · Accepted Answer · 2016-08-31 15:42:04Z

1

DHCP does more than just give you your IP address: it also gives you the Net Mask, the Gateway IP address, and the DNS Server IP address. If you don't call dhcpSetup(), you'll have to do it yourself.

According to the EtherCard documentation, you can do that as follows:

const static uint8_t ip[] = {192,168,0,100}; // Example
const static uint8_t gw[] = {192,168,0,254}; // Example
const static uint8_t dns[] = {192,168,0,1};  // Example

...

if (!ether.staticSetup(ip, gw, dns)
{
    // handle failure to configure static IP address
    // (current implementation always returns true!)
}

answered Aug 31, 2016 at 15:42

John Burger

1,8851 gold badge14 silver badges24 bronze badges

Thanks! I didn't know DNS lookup needed more than my ip address. I found my Gateway ip through an ipconfig command (windows), I'm currently searching what the DNS server ip address should be.

PHPirate
– PHPirate

2016-08-31 16:22:24 +00:00
Commented Aug 31, 2016 at 16:22
I found the dns ip with doing a DHCP setup and then printing ether.dnsip, and when I print it again after the static setup the ip shows correctly but still the dns lookup fails. Any idea what misses more?

PHPirate
– PHPirate

2016-08-31 16:28:39 +00:00
Commented Aug 31, 2016 at 16:28
A second look at the documentation solved it! I just had to add the netmask as well, after printing it (after DHCP) with ether.netmask.

PHPirate
– PHPirate

2016-08-31 16:32:30 +00:00
Commented Aug 31, 2016 at 16:32

Add a comment |

Juergen · Accepted Answer · 2017-01-22 15:44:11Z

1

the documentation of ethercard.h and examples doesn't fit the actual version of ethercard very well.

for static ip setup use:

ether.staticSetup(myip, gwip, dnsip, netmask);

then the dnslookup works. most examples use the old mymask name, that is replaced by netmask

answered Jan 22, 2017 at 15:44

Juergen

516 bronze badges

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