DNS Client Application¶

Overview¶

The DNS resolver or DNS client sample application implements a basic DNS resolver according to RFC 1035. Supported DNS answers are: IPv4/IPv6 addresses and CNAME.

If a CNAME is received, the DNS resolver will create another DNS query. The number of additional queries is controlled by the DNS_RESOLVER_ADDITIONAL_QUERIES Kconfig variable.

For more information about DNS configuration variables, see: subsys/net/lib/dns/Kconfig. The DNS resolver API can be found at include/net/dns_client.h. The sample code can be found at: samples/net/dns_client.

The return codes used by this sample application are described by the following table.

Macro	Value	Description
-EINVAL	-22	if an invalid parameter was detected
-EIO	-5	network error
-ENOMEM	-12	memory error, perhaps related to network buffers

A return code of 0 must be interpreted as success.

Requirements¶

networking with Qemu
screen terminal emulator or equivalent.
For the Arduino 101 board, the ENC28J60 Ethernet module is required.
dnsmasq application. The dnsmasq version used in this sample is:

dnsmasq -v
Dnsmasq version 2.76  Copyright (c) 2000-2016 Simon Kelley

Wiring¶

The ENC28J60 module is an Ethernet device with SPI interface. The following pins must be connected from the ENC28J60 device to the Arduino 101 board:

Arduino 101	ENC28J60 (pin numbers on the board)
D13	SCK (1)
D12	SO (3)
D11	SI (2)
D10	CS (7)
D04	INT (5)
3.3V	VCC (10)
GDN	GND (9)

Building and Running¶

Network Configuration¶

Open the project configuration file for your platform, for example: prj_frdm_k64f.conf is the configuration file for the NXP FRDM-K64F board. For IPv4 networks, set the following variables:

CONFIG_NET_IPV4=y
CONFIG_NET_IPV6=n

IPv6 is the preferred routing technology for this sample application, if CONFIG_NET_IPV6=y is set, the value of CONFIG_NET_IPV4 is ignored.

In this sample application, only static IP addresses are supported, those addresses are specified in the project configuration file, for example:

CONFIG_NET_SAMPLES_MY_IPV6_ADDR="2001:db8::1"
CONFIG_NET_SAMPLES_PEER_IPV6_ADDR="2001:db8::2"

are the IPv6 addresses for the DNS client running Zephyr and the DNS server, respectively.

Alternatively, the IP addresses may be specified in the samples/net/dns_client/src/config.h file.

Open the samples/net/dns_client/src/config.h file and set the server port to match the DNS server setup, for example:

#define REMOTE_PORT          5353

assumes that the DNS server is listening at UDP port 5353.

DNS server¶

The dnsmasq tool may be used for testing purposes. Open a terminal window and type:

$ dnsmasq -p 5353 -d

NOTE: some systems may require root privileges to run dnsmaq, use sudo or su.

If dnsmasq fails to start with an error like this:

dnsmasq: failed to create listening socket for port 5353: Address already in use

Open a terminal window and type:

$ killall -s KILL dnsmasq

Try to launch the dnsmasq application again.

QEMU x86¶

Open a terminal window and type:

$ make

Run ‘loop_socat.sh’ and ‘loop-slip-tap.sh’ as indicated at:

https://gerrit.zephyrproject.org/r/gitweb?p=net-tools.git;a=blob;f=README

Set the IPv4 ip address:

$ ip addr add 192.0.2.2/24 dev tap0

Open a terminal where the project was build (i.e. samples/net/dns_client) and type:

$ make run

FRDM K64F¶

Open a terminal window and type:

$ make BOARD=frdm_k64f

The FRDM K64F board is detected as a USB storage device. The board must be mounted (i.e. to /mnt) to ‘flash’ the binary:

$ cp outdir/frdm_k64f/zephyr.bin /mnt

See Freedom-K64F board documentation for more information about this board.

Open a terminal window and type:

$ screen /dev/ttyACM0 115200

Use ‘dmesg’ to find the right USB device.

Once the binary is loaded into the FRDM board, press the RESET button.

Arduino 101¶

Open a terminal window and type:

$ make BOARD=arduino_101

To load the binary in the development board follow the steps in Arduino/Genuino 101.

Open a terminal window and type:

$ screen /dev/ttyUSB0 115200

Use ‘dmesg’ to find the right USB device.

Once the binary is loaded into the Arduino 101 board, press the RESET button.

Sample Output¶

IPv4 (CONFIG_NET_IPV6=n, CONFIG_NET_IPV4=y)

To exit from QEMU enter: 'CTRL+a, x'

[QEMU] CPU: qemu32

-------------------------------------------
[run_dns:142] name: not_a_real_domain_name
rc: -5

-------------------------------------------
[run_dns:142] name: zephyrproject.org
rc: -22

-------------------------------------------
[run_dns:142] name: linux.org
[run_dns:159] 192.243.104.10

-------------------------------------------
[run_dns:142] name: www.zephyrproject.org
[run_dns:159] 140.211.169.8

-------------------------------------------
[run_dns:142] name: kernel.org
[run_dns:159] 149.20.4.69
[run_dns:159] 199.204.44.194
[run_dns:159] 198.145.20.140

-------------------------------------------
[run_dns:142] name: gerrit.zephyrproject.org
[run_dns:159] 199.19.213.246

-------------------------------------------
[run_dns:142] name: linuxfoundation.org
[run_dns:159] 140.211.169.4

-------------------------------------------
[run_dns:142] name: jira.zephyrproject.org
[run_dns:159] 199.19.213.246

-------------------------------------------
[run_dns:142] name: www.wikipedia.org
[run_dns:159] 208.80.153.224

-------------------------------------------
[run_dns:142] name: collabprojects.linuxfoundation.org
[run_dns:159] 140.211.169.4

IPv6 (CONFIG_NET_IPV6=y, CONFIG_NET_IPV4=n)

To exit from QEMU enter: 'CTRL+a, x'
[QEMU] CPU: qemu32

-------------------------------------------
[run_dns:142] name: not_a_real_domain_name
rc: -22

-------------------------------------------
[run_dns:142] name: zephyrproject.org
[run_dns:159] ff02::3

-------------------------------------------
[run_dns:142] name: www.zephyrproject.org
[run_dns:159] ff02::4

-------------------------------------------
[run_dns:142] name: gerrit.zephyrproject.org
[run_dns:159] ff02::5

-------------------------------------------
[run_dns:142] name: jira.zephyrproject.org
[run_dns:159] ff02::6

-------------------------------------------
[run_dns:142] name: jenkins.zephyrproject.org
[run_dns:159] ff02::7

-------------------------------------------
[run_dns:142] name: linuxfoundation.org
[run_dns:159] ff02::8

-------------------------------------------
[run_dns:142] name: www.linuxfoundation.org
[run_dns:159] ff02::9

-------------------------------------------
[run_dns:142] name: collabprojects.linuxfoundation.org
[run_dns:159] ff02::a

Note: IPv6 addresses obtained via dnsmasq and /etc/hosts.

Known Issues¶

The above sample contains a rc: -22 (-EINVAL). This is the expected behavior for that domain name.
If a lot of rc: -5 (-EIO) errors are flooding the screen, increment APP_SLEEP_MSECS to 500 or even 1000. See samples/net/dns_client/src/config.h.
IPv4: there is still an issue not yet isolated that causes the application to fail during the first two queries. The issue lies between L2 (ARP) and UDP and it only appears during application startup.