I am completely new to lxc-containers. I installed lxc-container (fedora 29 amd64) on my ubuntu 18.04 system. The linux container had no firewall command line tools. Therefore I installed iptables into my container and it installed successfully.

However I tried to configure the interfaces to drop all incoming and outgoing packets which did not work. I am giving you all the details here.

The command ip \a gave;

[root@fedora29 ~]# 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
7: eth0@if8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:16:3e:4c:d8:bf brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.0.3.52/24 brd 10.0.3.255 scope global dynamic eth0
       valid_lft 3456sec preferred_lft 3456sec
    inet6 fe80::216:3eff:fe4c:d8bf/64 scope link 
       valid_lft forever preferred_lft forever

I have iptables rules as follows;

[root@fedora29 ~]# iptables -L
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    

Therefore I added the following two rules

iptables --table filter --append INPUT --in-interface eth0@if8 --jump DROP
iptables --table filter --append OUTPUT --out-interface eth0@if8 --jump DROP

When I finally saved the configuration with

 iptables-save

[root@fedora29 ~]# iptables-save
# Generated by iptables-save v1.8.0 on Wed Feb 20 08:41:43 2019
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -i eth0@if8 -j DROP
-A OUTPUT -o eth0@if8 -j DROP
COMMIT
# Completed on Wed Feb 20 08:41:43 2019

However the same worked fine with my ubuntu host system, where the interface is named lxcbr0. Please let me know if I need to provide any additional information so that it could help me to make you understand the problem more clear