Вам надо было либо все команды выполнять с sudo
Клиент 18.04 (получает список папок на 16.04, но не заходит на 20.04 и Win10)
~ $ sudo ip link show; sudo ip addr show; sudo ip route show type unicast; sudo iptables-save
[sudo] пароль для ****:
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
link/ether 74:d0:2b:6b:63:c2 brd ff:ff:ff:ff:ff:ff
3: vboxnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 0a:00:27:00:00:00 brd ff:ff:ff:ff:ff:ff
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: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
link/ether 74:d0:2b:6b:63:c2 brd ff:ff:ff:ff:ff:ff
inet 192.168.159.204/24 brd 192.168.159.255 scope global dynamic noprefixroute enp4s0
valid_lft 24577sec preferred_lft 24577sec
inet6 fe80::76d0:2bff:fe6b:63c2/64 scope link noprefixroute
valid_lft forever preferred_lft forever
3: vboxnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 0a:00:27:00:00:00 brd ff:ff:ff:ff:ff:ff
inet 192.168.56.1/24 brd 192.168.56.255 scope global vboxnet0
valid_lft forever preferred_lft forever
inet6 fe80::800:27ff:fe00:0/64 scope link
valid_lft forever preferred_lft forever
default via 192.168.159.200 dev enp4s0 proto dhcp metric 100
169.254.0.0/16 dev enp4s0 scope link metric 1000
192.168.56.0/24 dev vboxnet0 proto kernel scope link src 192.168.56.1
192.168.159.0/24 dev enp4s0 proto kernel scope link src 192.168.159.204 metric 100
Сервер 16.04 (в качестве сервера доступен всем)
~$ sudo ip link show; sudo ip addr show; sudo ip route show type unicast; sudo iptables-save
[sudo] пароль для ****:
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether d0:50:99:13:ec:cf brd ff:ff:ff:ff:ff:ff
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
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: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether d0:50:99:13:ec:cf brd ff:ff:ff:ff:ff:ff
inet 192.168.159.202/24 brd 192.168.159.255 scope global dynamic eth0
valid_lft 20461sec preferred_lft 20461sec
inet6 fe80::d250:99ff:fe13:eccf/64 scope link
valid_lft forever preferred_lft forever
default via 192.168.159.200 dev eth0 proto static metric 100
169.254.0.0/16 dev eth0 scope link metric 1000
192.168.159.0/24 dev eth0 proto kernel scope link src 192.168.159.202 metric 100
клиент и сервер 20.04 (в качестве сервера НЕ доступен с 18.04, в качестве клиента нормально получает список папок на 16.04)
~ $ sudo ip link show; sudo ip addr show; sudo ip route show type unicast; sudo iptables-save
[sudo] пароль для *****:
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 74:d4:35:8a:27:05 brd ff:ff:ff:ff:ff:ff
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: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 74:d4:35:8a:27:05 brd ff:ff:ff:ff:ff:ff
inet 192.168.159.207/24 brd 192.168.159.255 scope global dynamic noprefixroute enp1s0
valid_lft 16220sec preferred_lft 16220sec
inet6 fe80::77bb:3ec:7021:bd85/64 scope link noprefixroute
valid_lft forever preferred_lft forever
default via 192.168.159.200 dev enp1s0 proto dhcp metric 100
169.254.0.0/16 dev enp1s0 scope link metric 1000
192.168.159.0/24 dev enp1s0 proto kernel scope link src 192.168.159.207 metric 100