Questions[ipv4](ubuntu)

Im having trouble pinging google.com on ubuntu 20.04

david@Ptolemy:~$ ping google.com
PING google.com(syd09s22-in-x0e.1e100.net (2404:6800:4006:80e::200e)) 56 data bytes
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=1 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=2 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=3 Destination unreachable: Address unreachable
^C
--- google.com ping statistics ---
6 packets transmitted, 0 received, +3 errors, 100% packet loss, time 5071ms

I can ping google from my windows computer on the same network.

I can ping from my ubuntu computer the default gateway

david@Ptolemy:~$ ip r
default via 10.0.0.138 dev eno1 proto dhcp metric 100 
10.0.0.0/24 dev eno1 proto kernel scope link src 10.0.0.28 metric 100 
169.254.0.0/16 dev eno1 scope link metric 1000 

david@Ptolemy:~$ ping 10.0.0.138
PING 10.0.0.138 (10.0.0.138) 56(84) bytes of data.
64 bytes from 10.0.0.138: icmp_seq=1 ttl=64 time=0.528 ms
64 bytes from 10.0.0.138: icmp_seq=2 ttl=64 time=0.492 ms
64 bytes from 10.0.0.138: icmp_seq=3 ttl=64 time=0.491 ms
64 bytes from 10.0.0.138: icmp_seq=4 ttl=64 time=0.491 ms
64 bytes from 10.0.0.138: icmp_seq=5 ttl=64 time=0.565 ms
64 bytes from 10.0.0.138: icmp_seq=6 ttl=64 time=0.507 ms
^C
--- 10.0.0.138 ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5113ms
rtt min/avg/max/mdev = 0.491/0.512/0.565/0.027 ms

Here is some other settings:

david@Ptolemy:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    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: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 04:92:26:5c:a2:ea brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.28/24 brd 10.0.0.255 scope global dynamic noprefixroute eno1
       valid_lft 85865sec preferred_lft 85865sec
    inet6 2001:8003:7405:1200:b479:aa32:55aa:acf5/64 scope global temporary dynamic 
       valid_lft 2911sec preferred_lft 2911sec
    inet6 2001:8003:7405:1200:88b2:8fdf:2a6e:c736/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2911sec preferred_lft 2911sec
    inet6 fe80::318d:29eb:dfbb:ab2e/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

and my iptables has default rules as below:

david@Ptolemy:~$ sudo iptables -L
[sudo] password for david: 
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination  

Does anybody have an idea of how this can be fixed? Thanks.

UPDATE Re: @Jurrie questions I tried ping -4 google.com on both machines, and it does work. I then explicity tried ping -6 google.com on both machines. That delivers the same destination unreachable error now on both machines, so we are on the right track thanks to you.

david@Ptolemy:~$ ip -6 r
::1 dev lo proto kernel metric 256 pref medium
2001:8003:7405:1200::/64 via fe80::faab:5ff:feca:8050 dev eno1 proto ra metric 100 pref medium
fe80::/64 dev eno1 proto kernel metric 100 pref medium
default via fe80::faab:5ff:feca:8050 dev eno1 proto ra metric 20100 pref medium

So I went into my gateway page and the network settings "Local IPv4 Address" is set to the one we have seen 10.0.0.138, however in this table down the bottom there are two IPv6 settings that are left blank, ie. not set. Link Local Gateway IPv6 Address Globale Gateway IPv6 Address

I will have to find out how to configure ipv6 for my gateway I believe, or do I configure ubuntu to use ipv4. Which is more preferred?

More testing results and strange behaviour -

I changed the gai.conf back to the original state by commenting out your advised line precedence ::ffff:0:0/96 100 rebooted and then ran the following tests. Note how pinging google with no options fails with host unreachable message, where pining amazon works. Then note that ping -6 does not work for either, but producing different messages. I'm thinking that ubuntu is back to using ipv6 for ping, but why is the amazon.com working with normal ping if this is so?

david@Ptolemy:~$ ping www.google.com
PING www.google.com(syd09s23-in-x04.1e100.net (2404:6800:4006:80f::2004)) 56 data bytes
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=1 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=2 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=3 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=4 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=5 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=6 Destination unreachable: Address unreachable
^X^C
--- www.google.com ping statistics ---
8 packets transmitted, 0 received, +6 errors, 100% packet loss, time 7090ms

david@Ptolemy:~$ ping www.amazon.com
PING d3ag4hukkh62yn.cloudfront.net (13.224.176.180) 56(84) bytes of data.
64 bytes from server-13-224-176-180.syd1.r.cloudfront.net (13.224.176.180): icmp_seq=1 ttl=244 time=22.1 ms
64 bytes from server-13-224-176-180.syd1.r.cloudfront.net (13.224.176.180): icmp_seq=2 ttl=244 time=21.9 ms
64 bytes from server-13-224-176-180.syd1.r.cloudfront.net (13.224.176.180): icmp_seq=3 ttl=244 time=21.8 ms
^X64 bytes from server-13-224-176-180.syd1.r.cloudfront.net (13.224.176.180): icmp_seq=4 ttl=244 time=21.7 ms
^C
--- d3ag4hukkh62yn.cloudfront.net ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 21.661/21.860/22.090/0.160 ms
david@Ptolemy:~$ ping -6 www.google.com
PING www.google.com(syd09s23-in-x04.1e100.net (2404:6800:4006:80f::2004)) 56 data bytes
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=1 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=2 Destination unreachable: Address unreachable
From 2001:8003:7405:1200:faab:5ff:feca:8050 (2001:8003:7405:1200:faab:5ff:feca:8050) icmp_seq=3 Destination unreachable: Address unreachable
^C
--- www.google.com ping statistics ---
4 packets transmitted, 0 received, +3 errors, 100% packet loss, time 3026ms

david@Ptolemy:~$ ping -6 www.amazon.com
ping: www.amazon.com: Name or service not known
david@Ptolemy:~$ ping -4 www.google.com
PING www.google.com (142.250.66.196) 56(84) bytes of data.
64 bytes from syd09s23-in-f4.1e100.net (142.250.66.196): icmp_seq=1 ttl=115 time=22.3 ms
64 bytes from syd09s23-in-f4.1e100.net (142.250.66.196): icmp_seq=2 ttl=115 time=27.1 ms
64 bytes from syd09s23-in-f4.1e100.net (142.250.66.196): icmp_seq=3 ttl=115 time=22.3 ms
64 bytes from syd09s23-in-f4.1e100.net (142.250.66.196): icmp_seq=4 ttl=115 time=22.3 ms
64 bytes from syd09s23-in-f4.1e100.net (142.250.66.196): icmp_seq=5 ttl=115 time=21.9 ms
^X64 bytes from syd09s23-in-f4.1e100.net (142.250.66.196): icmp_seq=6 ttl=115 time=22.2 ms
^C
--- www.google.com ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5007ms
rtt min/avg/max/mdev = 21.931/23.008/27.081/1.825 ms
david@Ptolemy:~$ ping -4 www.amazon.com
PING e15316.e22.akamaiedge.net (23.217.176.20) 56(84) bytes of data.
64 bytes from a23-217-176-20.deploy.static.akamaitechnologies.com (23.217.176.20): icmp_seq=1 ttl=60 time=9.58 ms
64 bytes from a23-217-176-20.deploy.static.akamaitechnologies.com (23.217.176.20): icmp_seq=2 ttl=60 time=9.31 ms
64 bytes from a23-217-176-20.deploy.static.akamaitechnologies.com (23.217.176.20): icmp_seq=3 ttl=60 time=9.36 ms
^C
--- e15316.e22.akamaiedge.net ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 9.305/9.414/9.578/0.117 ms

TL;DR

Does anyone have a working netplan configuration that sets a dynamic IPv4 and a static IPv6 under Ubuntu Server 20.04?

What works

My provider (OVH) gave me a server with this configuration in /etc/netplan/50-cloud-init.yaml out of the box:

# This file is generated from information provided by the datasource.  Changes
# to it will not persist across an instance reboot.  To disable cloud-init's
# network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    version: 2
    ethernets:
        ens3:
            dhcp4: true
            match:
                macaddress: xx:yy:zz:aa:bb:cc
            mtu: 1500
            set-name: ens3

So the server is obtaining an IPv4 address through DHCP. Everything works here.

The issue

But, they also gave a static IPv6 (found from the web console management for this server) which is not present in the netplan configuration.

I tried to add it manually, using snippet like:

network:
    version: 2
    ethernets:
        ens3:
            dhcp6: false
            match:
                name: ens3
            addresses:
              - "dead:beef:404:200::cafe/128"
            gateway6: "dead:beef:404:200::1"

But nothing works: if the IPv4 works I have no IPv6, and if I get an IPv6 it revokes my IPv4 and I lose access to the server.

The try

I just tried this exact configuration in /etc/netplan/60-test-askubuntu.yaml after renamed all other files with .yaml.bak:

network:
    version: 2
    ethernets:
        ens3:
            dhcp6: false
            addresses:
              - "2001:41d0:206:cd1d::6153/128"
            gateway6: "2001:41d0:206:cd1d::1"
            dhcp4: true
            mtu: 1500

Result: the IPv4 is still working but I guess it will fail when the DHCP bail will be expired. The IPv6 address is set, but the gateway is not set so I cannot ping6 an IPv6 address:

user@server:/etc/netplan$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    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: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether fa:16:3e:23:28:1f brd ff:ff:ff:ff:ff:ff
    inet 51.210.xx.yy/32 scope global dynamic ens3
       valid_lft 86396sec preferred_lft 86396sec
    inet6 2001:41d0:206:cd1d::6153/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fe23:281f/64 scope link 
       valid_lft forever preferred_lft forever
user@server:/etc/netplan$ ip route
default via 51.210.8.1 dev ens3 proto dhcp src 51.210.xx.yy metric 100 
51.210.8.1 dev ens3 proto dhcp scope link src 51.210.xx.yy metric 100 
user@server:/etc/netplan$ ping google.com
PING google.com (172.217.22.142) 56(84) bytes of data.
64 bytes from par21s12-in-f14.1e100.net (172.217.22.142): icmp_seq=1 ttl=51 time=6.16 ms
64 bytes from par21s12-in-f14.1e100.net (172.217.22.142): icmp_seq=2 ttl=51 time=6.19 ms
^C
--- google.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 6.161/6.177/6.194/0.016 ms
user@server:/etc/netplan$ ping6 google.com
ping6: connect: Network is unreachable
user@server:/etc/netplan$ ip route
default via 51.210.8.1 dev ens3 proto dhcp src 51.210.xx.yy metric 100 
51.210.8.1 dev ens3 proto dhcp scope link src 51.210.xx.yy metric 100 
user@server:/etc/netplan$ ip -6 route
::1 dev lo proto kernel metric 256 pref medium
2001:41d0:206:cd1d::6153 dev ens3 proto kernel metric 256 pref medium
fe80::/64 dev ens3 proto kernel metric 256 pref medium

Question

Does anyone have a working netplan configuration for a dynamic IPv4 and a static IPv6?

It works when I set it manually using ip addr and ip route but I want a permanent configuration using netplan.

I try to install a server from scratch with a fixed IP address. For installation I use the provided ISO of 18.04.3 and the installation agent of Ubuntu.

First I thought that my understanding of the subnet CIDR was wrong, but after I received credible information from https://networkengineering.stackexchange.com/questions/63499/how-to-interpret-subnet-mask I am sure that this is more a problem within Ubuntu.

When I enter 255.255.252.0/22 as subnet CIDR and 10.16.192.252 as the IP address I get the error message that 10.16.192.251 is not contained in 255.255.252.0/22. But a subnet calculator tells me that 10.16.192.1 - 10.16.195.254 would be part of the subnet.

I want to create a pure IPv6 environment or disable IPv4 completely, not just on the interface. If it is impossible, I want to disable IPv4 on boot via the command line or a configuration file.

I've got a new laptop running Ubuntu 16.04 that worked like a charm for a couple of weeks but has now lost its appetite for connecting to the internet via Wi-fi. I know it's not a problem with my router or ISP, because I'm writing this post using my old Windows laptop on the exact same home network by Ubuntu laptop won't connect to.

I'm connecting to my router successfully, and running nmcli dev shows that I'm connected to my wifi device (wlp2s0) and to the wireless network.

Last night I was able to open some pages (Google, Facebook, YouTube), but not others (ubuntu.com, riken.jp). At the time I suspected it was something where IPv6 was working but IPv4 wasn't. Now, however, nothing works. Chromium, ping, wget, dig -- nothing. /etc/resolv.conf/ contains nothing at all (beyond the comment lines telling me not to edit it), and the table returned by route is empty.

UPDATE 1: I used ipconfig /all on my Windows machine to figure out which DNS servers it was using (75.75.75.75, 75.75.76.76., 2001:558:feed::1, 2001:558:feed::2), then used Network Connections to add these as DNS Servers for my home network. cat /etc/resolv.conf now gives me nameserver 127.0.1.1; I'm not entirely sure what this means, but I think it's some kind of alias, right? nmcli dev show | grep DNS shows me as using the two IPv6 DNS servers (2001:558:feed::1 and 2001:558:feed::2).

I can get wget to work with URLs that resolve to an IPv6 address, like so:

craig@craig-XPS-13-9370:~$ wget www.google.com
--2018-04-14 13:06:17--  http://www.google.com/
Resolving www.google.com (www.google.com)... 2607:f8b0:4004:808::2004, 
172.217.13.68
Connecting to www.google.com 
(www.google.com)|2607:f8b0:4004:808::2004|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Saving to: ‘index.html.5’

index.html.5            [ <=>                ]  10.41K  --.-KB/s    in 0.003s  

2018-04-14 13:06:17 (3.36 MB/s) - ‘index.html.5’ saved [10659]

I can't get a wget request to work with URLs that resolve to an IPv4 address:

craig@craig-XPS-13-9370:~$ wget www.ubuntu.com
--2018-04-14 13:06:28--  http://www.ubuntu.com/
Resolving www.ubuntu.com (www.ubuntu.com)... 91.189.89.118
Connecting to www.ubuntu.com (www.ubuntu.com)|91.189.89.118|:80... failed: 
Network is unreachable.

Adding the -4 flag to wget to force IPv4 usage gets a similar result:

craig@craig-XPS-13-9370:~$ wget -4 www.google.com
--2018-04-14 13:06:41--  http://www.google.com/
Resolving www.google.com (www.google.com)... 172.217.13.68
Connecting to www.google.com (www.google.com)|172.217.13.68|:80... failed: 
Network is unreachable.

Similarly, ping www.google.com doesn't work, but ping6 www.google.com does. So it's pretty clear that something is wrong with IPv4, but I'm not sure what...

UPDATE 2: I thought my problem looked pretty similar to this question, but the solution suggested there (disabling IPv4 via Network Connections) doesn't seem to have affected anything. It did give me some ideas for what it's useful to share with others, though:

Output from cat /etc/network/interfaces:

craig@craig-XPS-13-9370:~$ cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

Output from ifconfig:

craig@craig-XPS-13-9370:~$ ifconfig
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:13526 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13526 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:1031920 (1.0 MB)  TX bytes:1031920 (1.0 MB)

wlp2s0    Link encap:Ethernet  HWaddr 9c:b6:d0:8b:4b:c5  
          inet6 addr: fe80::1f3b:5545:508:919a/64 Scope:Link
          inet6 addr: 2601:140:8600:e0:d64b:9272:665f:3734/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:19665 errors:0 dropped:0 overruns:0 frame:0
          TX packets:10262 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:14731745 (14.7 MB)  TX bytes:1722860 (1.7 MB)

Output from iwconfig:

craig@craig-XPS-13-9370:~$ iwconfig
lo        no wireless extensions.

wlp2s0    IEEE 802.11abgn  ESSID:"MOTOROLA-ABD39"  
          Mode:Managed  Frequency:2.447 GHz  Access Point: 34:1F:E4:E4:35:D0   
          Bit Rate=1 Mb/s   Tx-Power=20 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:on
          Link Quality=55/70  Signal level=-55 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:39   Missed beacon:0

Output from cat /etc/resolv.conf:

craig@craig-XPS-13-9370:~$ 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

Output from route -n:

craig@craig-XPS-13-9370:~$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface

Output from route -6 -n:

craig@craig-XPS-13-9370:~$ route -6 -n
Kernel IPv6 routing table
Destination                    Next Hop                   Flag Met Ref Use If
2601:140:8600:e0::/64          ::                         U    600 0     0 wlp2s0
2601:140:8600:e0::/60          fe80::361f:e4ff:fee4:35cf  UG   600 0     0 wlp2s0
fe80::/64                      ::                         U    256 0     0 wlp2s0
::/0                           fe80::361f:e4ff:fee4:35cf  UG   600 2     4 wlp2s0
::/0                           ::                         !n   -1  1  1495 lo
::1/128                        ::                         Un   0   7    46 lo
2601:140:8600:e0:d64b:9272:665f:3734/128 ::                         Un   0   2   150 lo
fe80::1f3b:5545:508:919a/128   ::                         Un   0   2     4 lo
ff00::/8                       ::                         U    256 7    99 wlp2s0
::/0                           ::                         !n   -1  1  1495 lo

Output from ip neigh:

craig@craig-XPS-13-9370:~$ ip neigh
fe80::361f:e4ff:fee4:35cf dev wlp2s0 lladdr 34:1f:e4:e4:35:cf router REACHABLE