我有这个奇怪的问题，我不能closures端口21.我使用数字海洋运行Debian Stretch 9.我对我的域运行nmap ，它显示端口21是打开的。
作为参考的域名是： https : //fadverts.co.uk
我有一个防火墙设置，只允许以下端口：22,80,443。我已经尝试iptables和ufw无济于事。
这是从ufw status numbered输出：
[ 1] 22/tcp LIMIT IN Anywhere [ 2] 80/tcp ALLOW IN Anywhere [ 3] 443/tcp ALLOW IN Anywhere [ 4] 22/tcp (v6) LIMIT IN Anywhere (v6) [ 5] 80/tcp (v6) ALLOW IN Anywhere (v6) [ 6] 443/tcp (v6) ALLOW IN Anywhere (v6)
这是iptables的输出：
Chain INPUT (policy DROP) target prot opt source destination ufw-before-logging-input all -- 0.0.0.0/0 0.0.0.0/0 ufw-before-input all -- 0.0.0.0/0 0.0.0.0/0 ufw-after-input all -- 0.0.0.0/0 0.0.0.0/0 ufw-after-logging-input all -- 0.0.0.0/0 0.0.0.0/0 ufw-reject-input all -- 0.0.0.0/0 0.0.0.0/0 ufw-track-input all -- 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy DROP) target prot opt source destination ufw-before-logging-forward all -- 0.0.0.0/0 0.0.0.0/0 ufw-before-forward all -- 0.0.0.0/0 0.0.0.0/0 ufw-after-forward all -- 0.0.0.0/0 0.0.0.0/0 ufw-after-logging-forward all -- 0.0.0.0/0 0.0.0.0/0 ufw-reject-forward all -- 0.0.0.0/0 0.0.0.0/0 ufw-track-forward all -- 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT) target prot opt source destination ufw-before-logging-output all -- 0.0.0.0/0 0.0.0.0/0 ufw-before-output all -- 0.0.0.0/0 0.0.0.0/0 ufw-after-output all -- 0.0.0.0/0 0.0.0.0/0 ufw-after-logging-output all -- 0.0.0.0/0 0.0.0.0/0 ufw-reject-output all -- 0.0.0.0/0 0.0.0.0/0 ufw-track-output all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-after-forward (1 references) target prot opt source destination Chain ufw-after-input (1 references) target prot opt source destination ufw-skip-to-policy-input udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:137 ufw-skip-to-policy-input udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:138 ufw-skip-to-policy-input tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:139 ufw-skip-to-policy-input tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:445 ufw-skip-to-policy-input udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:67 ufw-skip-to-policy-input udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:68 ufw-skip-to-policy-input all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type BROADCAST Chain ufw-after-logging-forward (1 references) target prot opt source destination LOG all -- 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW BLOCK] " Chain ufw-after-logging-input (1 references) target prot opt source destination LOG all -- 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW BLOCK] " Chain ufw-after-logging-output (1 references) target prot opt source destination Chain ufw-after-output (1 references) target prot opt source destination Chain ufw-before-forward (1 references) target prot opt source destination ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 4 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 11 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 12 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 8 ufw-user-forward all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-before-input (1 references) target prot opt source destination ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED ufw-logging-deny all -- 0.0.0.0/0 0.0.0.0/0 ctstate INVALID DROP all -- 0.0.0.0/0 0.0.0.0/0 ctstate INVALID ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 4 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 11 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 12 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmptype 8 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp spt:67 dpt:68 ufw-not-local all -- 0.0.0.0/0 0.0.0.0/0 ACCEPT udp -- 0.0.0.0/0 224.0.0.251 udp dpt:5353 ACCEPT udp -- 0.0.0.0/0 239.255.255.250 udp dpt:1900 ufw-user-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-before-logging-forward (1 references) target prot opt source destination Chain ufw-before-logging-input (1 references) target prot opt source destination Chain ufw-before-logging-output (1 references) target prot opt source destination Chain ufw-before-output (1 references) target prot opt source destination ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED ufw-user-output all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-logging-allow (0 references) target prot opt source destination LOG all -- 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW ALLOW] " Chain ufw-logging-deny (2 references) target prot opt source destination RETURN all -- 0.0.0.0/0 0.0.0.0/0 ctstate INVALID limit: avg 3/min burst 10 LOG all -- 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW BLOCK] " Chain ufw-not-local (1 references) target prot opt source destination RETURN all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL RETURN all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type MULTICAST RETURN all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type BROADCAST ufw-logging-deny all -- 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 10 DROP all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-reject-forward (1 references) target prot opt source destination Chain ufw-reject-input (1 references) target prot opt source destination Chain ufw-reject-output (1 references) target prot opt source destination Chain ufw-skip-to-policy-forward (0 references) target prot opt source destination DROP all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-skip-to-policy-input (7 references) target prot opt source destination DROP all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-skip-to-policy-output (0 references) target prot opt source destination ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-track-forward (1 references) target prot opt source destination Chain ufw-track-input (1 references) target prot opt source destination Chain ufw-track-output (1 references) target prot opt source destination ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 ctstate NEW ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 ctstate NEW Chain ufw-user-forward (1 references) target prot opt source destination Chain ufw-user-input (1 references) target prot opt source destination tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 ctstate NEW recent: SET name: DEFAULT side: source mask: 255.255.255.255 ufw-user-limit tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 ctstate NEW recent: UPDATE seconds: 30 hit_count: 6 name: DEFAULT side: source mask: 255.255.255.255 ufw-user-limit-accept tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 Chain ufw-user-limit (1 references) target prot opt source destination LOG all -- 0.0.0.0/0 0.0.0.0/0 limit: avg 3/min burst 5 LOG flags 0 level 4 prefix "[UFW LIMIT BLOCK] " REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable Chain ufw-user-limit-accept (1 references) target prot opt source destination ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-user-logging-forward (0 references) target prot opt source destination Chain ufw-user-logging-input (0 references) target prot opt source destination Chain ufw-user-logging-output (0 references) target prot opt source destination Chain ufw-user-output (1 references) target prot opt source destination
现在我正在使用ufw但使用iptables时遇到了同样的问题。 这是我testing的一个configuration，但仍然是端口21显示为开放：
iptables -t filter -F iptables -t filter -X iptables -t filter -P FORWARD DROP iptables -t filter -P INPUT DROP iptables -t filter -P OUTPUT DROP iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT iptables -t filter -A INPUT -i lo -j ACCEPT iptables -t filter -A OUTPUT -o lo -j ACCEPT iptables -t filter -A OUTPUT -p tcp --dport 53 -j ACCEPT iptables -t filter -A OUTPUT -p udp --dport 53 -j ACCEPT iptables -t filter -A INPUT -p tcp --dport 53 -j ACCEPT iptables -t filter -A INPUT -p udp --dport 53 -j ACCEPT iptables -t filter -A INPUT -p tcp --dport 22 -j ACCEPT iptables -t filter -A OUTPUT -p tcp --dport 22 -j ACCEPT iptables -t filter -A OUTPUT -p tcp --dport 80 -j ACCEPT iptables -t filter -A INPUT -p tcp --dport 80 -j ACCEPT iptables -t filter -A OUTPUT -p tcp --dport 443 -j ACCEPT iptables -t filter -A INPUT -p tcp --dport 443 -j ACCEPT
防火墙的工作原理是，如果我使用nc -l -p 5001创build一个服务器，并从外部扫描端口，它将被closures。
另外，如果我telnet到端口21连接：
telnet fadverts.co.uk 21 Trying 139.59.172.62... Connected to fadverts.co.uk. Escape character is '^]'.
任何想法发生了什么？