useradd -g netadm -d /home/rancid -m -s /bin/bash rancid 

Команда ssh-keygen не создаёт директорию .ssh, надо сделать руками.

mkdir ~/.ssh 
chmod 700 ~/.ssh

https://arstech.net/install-iptables-in-debian-11-bullseye/

Останавливаем nftables.

apt remove --auto-remove nftables
apt purge nftables

Ставим iptables

apt install iptables
apt install iptables-persistent

Пишем первые правила в “/etc/iptables/rules.v4”

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
#SSH
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -s x.x.x.x/32 -j ACCEPT
#LAST_RULES
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT

Пишем первые правила в “/etc/iptables/rules.v6”

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p ipv6-icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
#-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
#-A INPUT -d fe80::/64 -p udp -m udp --dport 546 -m state --state NEW -j ACCEPT
#LAST-RULES
-A INPUT -j REJECT --reject-with icmp6-adm-prohibited
-A FORWARD -j REJECT --reject-with icmp6-adm-prohibited
COMMIT

Запускаем iptables.

systemctl start iptables ip6tables 
systemctl status iptables ip6tables 
systemctl enable iptables ip6tables 
iptables -S

apt update 
apt install mc joe bind9-utils man traceroute htop iftop net-tools telnet tcpdump

apt update 
apt install openssh-server
systemctl status ssh
systemctl enable ssh

Если на этапе установки не дать ОС выход в интернет, то в списке репо будет только “cdrom:”.
После настройки ip-адреса не получится сделать “apt update”.

В “/etc/apt/sources.list” комментируем “deb cdrom:[De..” и раскомментируем и дописываем “deb http://deb.debian.org/debian/ bullseye main contrib non-free”
Приводим файл к виду:

root@swan1:~# cat /etc/apt/sources.list
# deb cdrom:[Debian GNU/Linux 11.7.0 _Bullseye_ - Official amd64 NETINST 20230429-11:49]/ bullseye main

#deb cdrom:[Debian GNU/Linux 11.7.0 _Bullseye_ - Official amd64 NETINST 20230429-11:49]/ bullseye main

# Line commented out by installer because it failed to verify:
deb http://security.debian.org/debian-security bullseye-security main
# Line commented out by installer because it failed to verify:
deb-src http://security.debian.org/debian-security bullseye-security main

# bullseye-updates, to get updates before a point release is made;
# see https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_updates_and_backports
# A network mirror was not selected during install.  The following entries
# are provided as examples, but you should amend them as appropriate
# for your mirror of choice.
#
deb http://deb.debian.org/debian/ bullseye main contrib non-free
#deb-src http://deb.debian.org/debian/ bullseye-updates main

Поднимаем интерфейс.

# ip -c link show 
# ip link set dev ens18 up

Задаем ip-адрес и маршрут по умолчанию.

# ip addr add x.x.x.x/24  dev ens18
# ip route add 0.0.0.0/0 via x.x.x.1

DNS.

# echo 'nameserver 8.8.8.8' > /etc/resolv.conf

Правим /etc/network/interfaces.

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

auto ens18
iface ens18 inet static
        address x.x.x.99
        netmask 255.255.255.0
        gateway x.x.x.1
        dns-nameservers 8.8.8.8

Перезапускаем networking.

systemctl start networking
systemctl enable networking