I have several containers running Ubuntu 20.04.
I am able to connect to the containers via SSH. I can also update the the containers using apt.
The problem is that I can no longer make connections to other hosts from within the containers, I think since I upgraded to LXD 5.1.
When I try to ping any external ip address it fails.
How can I diagnose this problem?
lxc info focal
Name: focal
Status: RUNNING
Type: container
Architecture: x86_64
PID: 65544
Created: 2020/11/23 10:16 GMT
Last Used: 2022/05/11 10:42 BST
Resources:
Processes: 113
CPU usage:
CPU usage (in seconds): 30
Memory usage:
Memory (current): 511.61MiB
Memory (peak): 543.86MiB
Swap (current): 1.11MiB
Swap (peak): 112.00KiB
Network usage:
eth0:
Type: broadcast
State: UP
Host interface: veth747c6e80
MAC address: 00:16:3e:1d:31:00
MTU: 1500
Bytes received: 169.74kB
Bytes sent: 157.94kB
Packets received: 1842
Packets sent: 1733
IP addresses:
inet: 10.165.251.237/24 (global)
inet6: fd42:8121:aac9:ec67:216:3eff:fe1d:3100/64 (global)
inet6: fe80::216:3eff:fe1d:3100/64 (link)
lo:
Type: loopback
State: UP
MTU: 65536
Bytes received: 65.31kB
Bytes sent: 65.31kB
Packets received: 823
Packets sent: 823
IP addresses:
inet: 127.0.0.1/8 (local)
inet6: ::1/128 (local)
I am wondering if this problem could be related to IP6? The host does not have IP6 configured.
Certain kinds of connection are working. For example, I can use nslookup from within a container:
root@focal:~# nslookup google.com
Server: 127.0.0.53
Address: 127.0.0.53#53
Non-authoritative answer:
Name: google.com
Address: 216.58.212.238
Name: google.com
Address: 2a00:1450:4009:80b::200e
But if I try to ping an IP address it fails:
root@focal:~# ping -c 10 216.58.212.238
PING 216.58.212.238 (216.58.212.238) 56(84) bytes of data.
--- 216.58.212.238 ping statistics ---
10 packets transmitted, 0 received, 100% packet loss, time 9203ms
lxc network list
+---------+----------+---------+-----------------+---------------------------+-------------+---------+---------+
| NAME | TYPE | MANAGED | IPV4 | IPV6 | DESCRIPTION | USED BY | STATE |
+---------+----------+---------+-----------------+---------------------------+-------------+---------+---------+
| docker0 | bridge | NO | | | | 0 | |
+---------+----------+---------+-----------------+---------------------------+-------------+---------+---------+
| lxdbr0 | bridge | YES | 10.165.251.1/24 | fd42:8121:aac9:ec67::1/64 | | 11 | CREATED |
+---------+----------+---------+-----------------+---------------------------+-------------+---------+---------+
| wlp59s0 | physical | NO | | | | 0 | |
+---------+----------+---------+-----------------+---------------------------+-------------+---------+---------+
ip a on host
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: wlp59s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 9c:b6:d0:ba:f3:33 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.2/24 brd 192.168.1.255 scope global dynamic noprefixroute wlp59s0
valid_lft 83888sec preferred_lft 83888sec
inet6 2a00:23a8:8e3:a901:5c3a:c062:1c85:d819/64 scope global temporary dynamic
valid_lft 230sec preferred_lft 50sec
inet6 2a00:23a8:8e3:a901:497e:c0ed:75ac:bbed/64 scope global dynamic mngtmpaddr noprefixroute
valid_lft 230sec preferred_lft 50sec
inet6 fe80::85e5:8a5e:77ae:6e7b/64 scope link noprefixroute
valid_lft forever preferred_lft forever
3: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
link/ether 02:42:ad:b9:c5:80 brd ff:ff:ff:ff:ff:ff
inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
valid_lft forever preferred_lft forever
5: lxdbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 00:16:3e:4d:ab:16 brd ff:ff:ff:ff:ff:ff
inet 10.165.251.1/24 scope global lxdbr0
valid_lft forever preferred_lft forever
inet6 fd42:8121:aac9:ec67::1/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::216:3eff:fe4d:ab16/64 scope link
valid_lft forever preferred_lft forever
11: veth5b3afa58@if10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master lxdbr0 state UP group default qlen 1000
link/ether 76:ee:91:5e:bb:d5 brd ff:ff:ff:ff:ff:ff link-netnsid 2
15: veth747c6e80@if14: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master lxdbr0 state UP group default qlen 1000
link/ether b2:bd:55:94:80:dd brd ff:ff:ff:ff:ff:ff link-netnsid 0
ip a in container
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
14: eth0@if15: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 00:16:3e:1d:31:00 brd ff:ff:ff:ff:ff:ff link-netnsid 0
inet 10.165.251.237/24 brd 10.165.251.255 scope global dynamic eth0
valid_lft 2310sec preferred_lft 2310sec
inet6 fd42:8121:aac9:ec67:216:3eff:fe1d:3100/64 scope global dynamic mngtmpaddr noprefixroute
valid_lft 3127sec preferred_lft 3127sec
inet6 fe80::216:3eff:fe1d:3100/64 scope link
valid_lft forever preferred_lft forever
Any help is very gratefully received. I have been using LXD for many years with no issues, but I am not very familiar with Linux networking configuration. 
Sounds like a firewall issue.
Please show sudo iptables-save and sudo nft list ruleset (if available).
Thanks for the reply!
sudo iptables-save
# Generated by iptables-save v1.8.4 on Wed May 11 11:36:11 2022
*nat
:PREROUTING ACCEPT [3958:598378]
:INPUT ACCEPT [2464:496382]
:OUTPUT ACCEPT [11162:937095]
:POSTROUTING ACCEPT [10899:900182]
:DOCKER - [0:0]
-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
-A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER
-A POSTROUTING -s 172.17.0.0/16 ! -o docker0 -j MASQUERADE
-A DOCKER -i docker0 -j RETURN
COMMIT
# Completed on Wed May 11 11:36:11 2022
# Generated by iptables-save v1.8.4 on Wed May 11 11:36:11 2022
*filter
:INPUT ACCEPT [617076:721790590]
:FORWARD DROP [1276:86774]
:OUTPUT ACCEPT [401992:48551234]
:DOCKER - [0:0]
:DOCKER-ISOLATION-STAGE-1 - [0:0]
:DOCKER-ISOLATION-STAGE-2 - [0:0]
:DOCKER-USER - [0:0]
-A FORWARD -j DOCKER-USER
-A FORWARD -j DOCKER-ISOLATION-STAGE-1
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A DOCKER-ISOLATION-STAGE-1 -i docker0 ! -o docker0 -j DOCKER-ISOLATION-STAGE-2
-A DOCKER-ISOLATION-STAGE-1 -j RETURN
-A DOCKER-ISOLATION-STAGE-2 -o docker0 -j DROP
-A DOCKER-ISOLATION-STAGE-2 -j RETURN
-A DOCKER-USER -j RETURN
COMMIT
# Completed on Wed May 11 11:36:11 2022
sudo nft list ruleset not available.
Ah, just saw:
Please see LXD and Docker Firewall Redux - How to deal with FORWARD policy set to drop - #3 by tomp
and we also have a section here:
Please let us know if that helps.
Thanks @tomp it was docker causing the issue. Thanks so much for your help 
