DNS resolution not working in DHCP

I noticed this strange behaviour, I have a wi-fi network that only works with static IP addresses. If I set DHCP the DNS resolution fails, I can for example ping 8.8.8.8 but I can't surf the web or ping It happens only with my computer, and only with the Ubuntu partition (no problem using Win10). I don't have any kind of problem with other wi-fi networks. My computer runs 16.04, everything updated. Any hints?

UPDATE

These are output from Ubuntu commands (not working)

$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever
2: enp7s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000 link/ether fc:3f:db:a2:6d:46 brd ff:ff:ff:ff:ff:ff
3: wlp19s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000 link/ether c8:ff:28:93:26:32 brd ff:ff:ff:ff:ff:ff inet 192.168.0.100/24 brd 192.168.0.255 scope global dynamic wlp19s0 valid_lft 7193sec preferred_lft 7193sec inet6 fe80::e9a0:6a46:1112:815/64 scope link valid_lft forever preferred_lft forever
$ ip route
default via 192.168.0.1 dev wlp19s0 proto static metric 600
169.254.0.0/16 dev wlp19s0 scope link metric 1000
192.168.0.0/24 dev wlp19s0 proto kernel scope link src 192.168.0.100 metric 600
$ cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.1.1

And this is from ipconfig /all in Win10 (working)

Scheda LAN wireless Wi-Fi: Suffisso DNS specifico per connessione: Descrizione . . . . . . . . . . . . . : Realtek RTL8188EE 802.11 bgn Wi-Fi Adapter Indirizzo fisico. . . . . . . . . . . : C8-FF-28-93-26-32 DHCP abilitato. . . . . . . . . . . . : Sì Configurazione automatica abilitata : Sì Indirizzo IPv6 locale rispetto al collegamento . : fe80::7d95:51a8:c887:792e%17(Preferenziale) Indirizzo IPv4. . . . . . . . . . . . : 192.168.0.100(Preferenziale) Subnet mask . . . . . . . . . . . . . : 255.255.255.0 Lease ottenuto. . . . . . . . . . . . : sabato 1 aprile 2017 10:12:04 Scadenza lease . . . . . . . . . . . : sabato 1 aprile 2017 12:12:18 Gateway predefinito . . . . . . . . . : 192.168.0.1 Server DHCP . . . . . . . . . . . . . : 192.168.0.1 IAID DHCPv6 . . . . . . . . . . . : 281607976 DUID Client DHCPv6. . . . . . . . : 00-01-00-01-1D-FD-6A-93-FC-3F-DB-A2-6D-46 Server DNS . . . . . . . . . . . . . : 192.168.0.1 NetBIOS su TCP/IP . . . . . . . . . . : Attivato

I also tried to factory reset the router, without any luck.. but I might found something interesting, after reset, I tried to connect to the router to change the settings via LAN cable, and was not able to connect using tplinkmodem.net , but only using 192.168.1.1. There is something bad in my local DNS resolution I think, but I'm not an expert.. so I'm waiting for suggestion!

2 Answers

This solution worked for me:

However I don't understand why. DHCP has always worked before in my Ubuntu.. If someone can explain what I did following the solution, would be great. thank you

This depends heavily on your router. While running Win10 (which works) check the network parameters your computer receives via DHCP with ipconfig /all. While running Ubuntu set to DHCP (which doesn't work), do the same with ip addr, ip route and cat /etc/resolv.conf. Compare the two to your router configuration to see where the difference might come from.

As your /etc/resolv.conf says nameserver 127.0.1.1 that shows you're running dnsmasq on Ubuntu (the default), so you'll have to check the dnsmasq configuration too. That's not so easy since it is managed dynamically by Network Manager via dbus, so there's no configuration file you can read, and regrettably there seems to be no way of querying dnsmasq's current configuration. Start by requesting a dnsmasq statistics reqort with

sudo killall -URS1 dnsmasq

and scanning the syslog for messages from dnsmasq with

grep dnsmasq /var/log/syslog

EDIT: Sorry I forgot about dnsmasq. As I'm not allowed to post comments I updated my answer.