Iptables
埠轉發到 OpenVPN 連接一次然後停止連接
我正在嘗試通過 OpenVPN 連接 (10.8.0.100) 將 IMAP 和 SMTP 埠從外部 IP 地址 (xxxx) 轉發到專用網路上的電腦。我目前有一個 OpenVPN 伺服器 (10.8.0.1)，它與外部 IP (xxxx) 存在於同一台機器上。
我使用 iptables 從 xxxx 轉發埠 993、587 和 143 到 10.8.0.100，我可以通過 telnet 從外部連接到任何這些埠並從內部 IMAP 和 SMTP 伺服器獲得響應，但是一旦我關閉連接，我無法重新連接一段時間（大約 30 秒）。如果我嘗試立即連接，它只會掛在那裡說“正在嘗試 xxxx ..”並且不會連接。如果我停止嘗試一段時間，然後再試一次，它會再次正常響應。但是如果我關閉連接，它會再次發生。
如果我在帶有 OpenVPN 伺服器本身的機器上，也會發生這種情況。如果我在埠 143 上 telnet 到 10.8.0.100，假設它會連接，然後如果我關閉連接並重試，它就在那裡。
root@x.x.x.x:~# telnet 10.8.0.100 143 Trying 10.8.0.100... Connected to 10.8.0.100. Escape character is '^]'. * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE STARTTLS AUTH=PLAIN] Dovecot ready. d d BAD Error in IMAP command received by server. d d BAD Error in IMAP command received by server. d * BYE Too many invalid IMAP commands. Connection closed by foreign host. root@x.x.x.x:~# telnet 10.8.0.100 143 Trying 10.8.0.100...現在，如果我進入 IMAP/SMTP 伺服器所在的專用網路中的電腦，我可以毫無問題地遠端登錄這些埠，關閉它們並儘快重新打開。
我一直在尋找幾天來嘗試解決此問題的方法，但我似乎無法在網路上找到與此問題相關的任何內容。任何幫助，將不勝感激。
更新 添加 iptables-save 輸出：
~# iptables-save # Generated by iptables-save v1.4.21 on Sat Sep 19 00:13:24 2015 *nat :PREROUTING ACCEPT [7476:440381] :INPUT ACCEPT [6361:381728] :OUTPUT ACCEPT [5842:414754] :POSTROUTING ACCEPT [5829:413974] -A PREROUTING -d x.x.x.x/32 -p tcp -m tcp --dport 993 -j DNAT --to-destination 10.8.0.100:993 -A PREROUTING -d x.x.x.x/32 -p tcp -m tcp --dport 587 -j DNAT --to-destination 10.8.0.100:587 -A PREROUTING -d x.x.x.x/32 -p tcp -m tcp --dport 143 -j DNAT --to-destination 10.8.0.100:143 -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -d 10.8.0.100/32 -p tcp -m tcp --dport 993 -j SNAT --to-source 10.8.0.1:993 -A POSTROUTING -d 10.8.0.100/32 -p tcp -m tcp --dport 587 -j SNAT --to-source 10.8.0.1:587 -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE -A POSTROUTING -d 10.8.0.100/32 -p tcp -m tcp --dport 143 -j SNAT --to-source 10.8.0.1:143 -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE COMMIT # Completed on Sat Sep 19 00:13:24 2015 # Generated by iptables-save v1.4.21 on Sat Sep 19 00:13:24 2015 *filter :INPUT DROP [42:2113] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] :ufw-after-forward - [0:0] :ufw-after-input - [0:0] :ufw-after-logging-forward - [0:0] :ufw-after-logging-input - [0:0] :ufw-after-logging-output - [0:0] :ufw-after-output - [0:0] :ufw-before-forward - [0:0] :ufw-before-input - [0:0] :ufw-before-logging-forward - [0:0] :ufw-before-logging-input - [0:0] :ufw-before-logging-output - [0:0] :ufw-before-output - [0:0] :ufw-logging-allow - [0:0] :ufw-logging-deny - [0:0] :ufw-not-local - [0:0] :ufw-reject-forward - [0:0] :ufw-reject-input - [0:0] :ufw-reject-output - [0:0] :ufw-skip-to-policy-forward - [0:0] :ufw-skip-to-policy-input - [0:0] :ufw-skip-to-policy-output - [0:0] :ufw-track-forward - [0:0] :ufw-track-input - [0:0] :ufw-track-output - [0:0] :ufw-user-forward - [0:0] :ufw-user-input - [0:0] :ufw-user-limit - [0:0] :ufw-user-limit-accept - [0:0] :ufw-user-logging-forward - [0:0] :ufw-user-logging-input - [0:0] :ufw-user-logging-output - [0:0] :ufw-user-output - [0:0] -A INPUT -j ufw-before-logging-input -A INPUT -j ufw-before-input -A INPUT -j ufw-after-input -A INPUT -j ufw-after-logging-input -A INPUT -j ufw-reject-input -A INPUT -j ufw-track-input -A INPUT -i eth0 -p tcp -m tcp --dport 993 -m state --state NEW,ESTABLISHED -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 587 -m state --state NEW,ESTABLISHED -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 143 -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT -A FORWARD -s 10.8.0.0/24 -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu -A FORWARD -j ufw-before-logging-forward -A FORWARD -j ufw-before-forward -A FORWARD -j ufw-after-forward -A FORWARD -j ufw-after-logging-forward -A FORWARD -j ufw-reject-forward -A FORWARD -j ufw-track-forward -A OUTPUT -j ufw-before-logging-output -A OUTPUT -j ufw-before-output -A OUTPUT -j ufw-after-output -A OUTPUT -j ufw-after-logging-output -A OUTPUT -j ufw-reject-output -A OUTPUT -j ufw-track-output -A OUTPUT -o eth0 -p tcp -m tcp --sport 993 -m state --state ESTABLISHED -j ACCEPT -A OUTPUT -o eth0 -p tcp -m tcp --sport 25 -m state --state ESTABLISHED -j ACCEPT -A OUTPUT -o eth0 -p tcp -m tcp --sport 587 -m state --state ESTABLISHED -j ACCEPT -A OUTPUT -o eth0 -p tcp -m tcp --sport 143 -m state --state ESTABLISHED -j ACCEPT -A ufw-after-input -p udp -m udp --dport 137 -j ufw-skip-to-policy-input -A ufw-after-input -p udp -m udp --dport 138 -j ufw-skip-to-policy-input -A ufw-after-input -p tcp -m tcp --dport 139 -j ufw-skip-to-policy-input -A ufw-after-input -p tcp -m tcp --dport 445 -j ufw-skip-to-policy-input -A ufw-after-input -p udp -m udp --dport 67 -j ufw-skip-to-policy-input -A ufw-after-input -p udp -m udp --dport 68 -j ufw-skip-to-policy-input -A ufw-after-input -m addrtype --dst-type BROADCAST -j ufw-skip-to-policy-input -A ufw-after-logging-input -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW BLOCK] " -A ufw-before-forward -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT -A ufw-before-forward -p icmp -m icmp --icmp-type 3 -j ACCEPT -A ufw-before-forward -p icmp -m icmp --icmp-type 4 -j ACCEPT -A ufw-before-forward -p icmp -m icmp --icmp-type 11 -j ACCEPT -A ufw-before-forward -p icmp -m icmp --icmp-type 12 -j ACCEPT -A ufw-before-forward -p icmp -m icmp --icmp-type 8 -j ACCEPT -A ufw-before-forward -j ufw-user-forward -A ufw-before-input -i lo -j ACCEPT -A ufw-before-input -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT -A ufw-before-input -m conntrack --ctstate INVALID -j ufw-logging-deny -A ufw-before-input -m conntrack --ctstate INVALID -j DROP -A ufw-before-input -p icmp -m icmp --icmp-type 3 -j ACCEPT -A ufw-before-input -p icmp -m icmp --icmp-type 4 -j ACCEPT -A ufw-before-input -p icmp -m icmp --icmp-type 11 -j ACCEPT -A ufw-before-input -p icmp -m icmp --icmp-type 12 -j ACCEPT -A ufw-before-input -p icmp -m icmp --icmp-type 8 -j ACCEPT -A ufw-before-input -p udp -m udp --sport 67 --dport 68 -j ACCEPT -A ufw-before-input -j ufw-not-local -A ufw-before-input -d y.y.y.y/32 -p udp -m udp --dport 5353 -j ACCEPT -A ufw-before-input -d z.z.z.z/32 -p udp -m udp --dport 1900 -j ACCEPT -A ufw-before-input -j ufw-user-input -A ufw-before-output -o lo -j ACCEPT -A ufw-before-output -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT -A ufw-before-output -j ufw-user-output -A ufw-logging-allow -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW ALLOW] " -A ufw-logging-deny -m conntrack --ctstate INVALID -m limit --limit 3/min --limit-burst 10 -j RETURN -A ufw-logging-deny -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW BLOCK] " -A ufw-not-local -m addrtype --dst-type LOCAL -j RETURN -A ufw-not-local -m addrtype --dst-type MULTICAST -j RETURN -A ufw-not-local -m addrtype --dst-type BROADCAST -j RETURN -A ufw-not-local -m limit --limit 30/min --limit-burst 10 -j ufw-logging-deny -A ufw-not-local -j DROP -A ufw-skip-to-policy-forward -j ACCEPT -A ufw-skip-to-policy-input -j DROP -A ufw-skip-to-policy-output -j ACCEPT -A ufw-track-forward -p tcp -m conntrack --ctstate NEW -j ACCEPT -A ufw-track-forward -p udp -m conntrack --ctstate NEW -j ACCEPT -A ufw-track-output -p tcp -m conntrack --ctstate NEW -j ACCEPT -A ufw-track-output -p udp -m conntrack --ctstate NEW -j ACCEPT -A ufw-user-input -p tcp -m tcp --dport 22 -j ACCEPT -A ufw-user-input -p udp -m udp --dport 22 -j ACCEPT -A ufw-user-input -p udp -m udp --dport 1194 -j ACCEPT -A ufw-user-input -p tcp -m tcp --dport 25 -j ACCEPT -A ufw-user-input -p tcp -m tcp --dport 587 -j ACCEPT -A ufw-user-input -p udp -m udp --dport 587 -j ACCEPT -A ufw-user-input -p tcp -m tcp --dport 465 -j ACCEPT -A ufw-user-input -p udp -m udp --dport 465 -j ACCEPT -A ufw-user-input -p tcp -m tcp --dport 993 -j ACCEPT -A ufw-user-input -p udp -m udp --dport 993 -j ACCEPT -A ufw-user-input -p tcp -m tcp --dport 143 -j ACCEPT -A ufw-user-input -p udp -m udp --dport 143 -j ACCEPT -A ufw-user-limit -m limit --limit 3/min -j LOG --log-prefix "[UFW LIMIT BLOCK] " -A ufw-user-limit -j REJECT --reject-with icmp-port-unreachable -A ufw-user-limit-accept -j ACCEPT COMMIT
**修復：**我決定從一組乾淨的 iptables 規則開始，執行以下操作：
iptables -F iptables --table nat --flush iptables --delete iptables --table nat --delete-chain iptables -F (maybe not necessary but did it at the end anyhow)我決定禁用 ufw 並使用 iptables 在埠 1194（OpenVPN 埠）上允許 udp。
iptables -I INPUT -p udp -m udp --dport 1194 -j ACCEPT然後使用https://unix.stackexchange.com/questions/76300/iptables-port-to-another-ip-port-from-the-inside作為我的指導，我做了以下事情：
iptables -t nat -A PREROUTING -p tcp --dport 143 -d x.x.x.x -j DNAT --to-destination 10.8.0.100 iptables -t nat -A POSTROUTING -p tcp --dport 143 -d 10.8.0.100 -j SNAT --to-source 10.8.0.1 iptables -A FORWARD -p tcp --dport 143 -d 10.8.0.100 -j ACCEPT現在，我可以遠端登錄到埠 143，關閉連接並立即重新打開連接，而無需等待。我對所有 IMAP(S) 和 SMTP(S) 埠都這樣做了。