Commands#

> ls -la /usr/sbin/ip*  # list all commands, there are many
> iptables*             # for ipv4 (in debian busters = nft)
> ip6tables*            # for ipv6 (in debian busters = nft)
> iptables-legacy       # former ones, not nft
> iptables-nft          # directly use nft

• all iptables commands (for ipv4) have an ip6tables* equivalent (for ipv6)
• see info on nft

> who -u                      # get all sessions with ip and pid
> sudo netstat -pantW         # list network connections, p=programs,a=all,n=IPs,t=tcp,W=wide(not truncate IP address) 
> ip a                        # list all ips
> sudo ip6tables -L -v        # list all ipv6 rules
> sudo ip6tables -n -v --line-numbers -L     # list all ipv6 rules with numeric IPs and rule number

Syntax#

> sudo iptables -L -v 
> sudo iptables -nvL                    # thjis is most compact
> sudo iptables -n -v --line-numbers -L 
> sudo service iptables start		# activate firewalling
> sudo service ip6tables start
> sudo chkconfig iptables on		# enable after reboot
> sudo chkconfig ip6tables on

iptables [-t <table-name>] <command> <chain-name> <parameter-1>  <option-1> <parameter-n> <option-n>

• table-name
  • like [filter, nat, mangle, raw, security], if omitted we use "filter"
• command
  • -F : flush current chain or all if omitted
  • -X : deletes a user-specified chain or all if omitted
  • -Z : zeros the byte and packet counters in all chains
  • -A : apppend a rule at the end
  • -I : inserts at a specified position (similar to replace -R), wihtout position at the top
  • -P : a policy is a fall back and is used after all rules have passede** you can enable certain special addresses earlier
  • -L : list all rules
• chain-name
  • INPUT, FORWARD, OUTPUT (as listed with > iptables -L)
  • you may invent new chain names, but this seems not to be common (command -N)
• parameter-1 (filter)
  • -s : source filter (address[/mask][...])
  • -d : destination filter
  • -p : protocoll filter like [icmp, tcp, udp, all] or those in /etc/protocols, if omitted ALL protocols are considered
    • with -p tcp you can use --dport for destination port filter, any number
    • with -p udp you can use --dport for destination port and --sport as source port filter
    • ports can be also a range like 3000:3200 (all from 3000 to 3200)
    • with -p icmp you can use --icmp-type
  • -i : interface like [eth0, lo, ppp0], without name ALL interfaces are used
  • -j : jump to [ACCEPT, DROP, QUEUE, RETURN] (or others added with modules)
  • -m : adds a comment when listing the rules, syntax >-m comment --comment "My comments here"<
• option-1 (target)
  • [ACCEPT, DROP, QUEUE, RETURN] (or others added with modules)
• option-n (listing options)
  • -v : verbose output
  • -n : displays IP addresses and port numbers in numeric format instead of hostname/network service
• notes
  • the first three commands are usually used to create a fresh ruleset in a script
  • in the chain list and then drop all other later

4. my general ruleset#

We also need to enable the local interface and the DNS nameservers.
I use a custom DNS server setting, because the fritzbox does not resolve my dynv6 domains (?).

> sudo nmcli -o device show	    # show interfaces settings
> sudo nmcli -p connection show	    # show interface status

#THIS IS NECESSARY
> sudo nmcli con mod "Wired connection 1" ipv4.dns "1.1.1.1,8.8.8.8"                # add cloudflare and google dns
> sudo nmcli con mod "Wired connection 1" ipv4.ignore-auto-dns no                   # this adds "search fritz.box" to get ips at all from frit.box
> sudo nmcli con mod "Wired connection 1" ipv6.ignore-auto-dns yes                  # we skip ipv6 dns
> sudo nmcli c down "Wired connection 1" && sudo nmcli c up "Wired connection 1"    # restart
> sudo vi /etc/resolv.conf    # validate settings

#!/bin/bash
# MARKUS
SOURCE=::

# ipv4 ------------------------------------
# Flush all rules and delete all chains for a clean startup
iptables -F
iptables -X
iptables -Z             # Zero out all counters

# drop all ipv4 traffic, we want to use ipv6 only
iptables -A INPUT -s 1.1.1.1 -j ACCEPT
iptables -A OUTPUT -d 1.1.1.1 -j ACCEPT
iptables -A INPUT -s 8.8.8.8 -j ACCEPT
iptables -A OUTPUT -d 8.8.8.8 -j ACCEPT

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
iptables -A INPUT -j DROP
iptables -A FORWARD -j DROP
iptables -A OUTPUT -j DROP

# ipv6 ------------------------------------
# Flush all rules and delete all chains for a clean startup
ip6tables -F
ip6tables -X
ip6tables -Z

# drop all ipv6 traffic, except EbelStube
# do not limit to --dport 22, because the source has random ports (?)
# add first to enabel replacing 1. rule later
ip6tables -A INPUT  -s $SOURCE -j ACCEPT
ip6tables -A OUTPUT -d $SOURCE -j ACCEPT

# allow ipv6 local loopback
ip6tables -A INPUT -i lo -j ACCEPT
ip6tables -A OUTPUT -o lo -j ACCEPT

# drop everthing else
ip6tables -P FORWARD DROP               # as policy generally
ip6tables -A INPUT  -j DROP
ip6tables -A OUTPUT -j DROP

# update first ip6tables rules and enable my computer
/home/markus/update_ip6tables.py