IPTables：允许传出 SSH

Question 1

当您有传出连接时，目标端口将为 22，因此规则应为：

$IPT -A OUTPUT -o eth0 -p tcp --dport 22 -j ACCEPT

此外，您应该有一条规则来涵盖ESTABLISHED和位于和链RELATED之上：INPUTOUTPUT

$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

希望这可以帮助。

Answer

当您有传出连接时，目标端口将为 22，因此规则应为：

$IPT -A OUTPUT -o eth0 -p tcp --dport 22 -j ACCEPT

此外，您应该有一条规则来涵盖ESTABLISHED和位于和链RELATED之上：INPUTOUTPUT

$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

希望这可以帮助。

Question 2

您的传出 SSH 流量规则不包含NEW启动传出连接所需的语句。

Answer

您的传出 SSH 流量规则不包含NEW启动传出连接所需的语句。

Question 3

如果你不了解客户端-服务器架构和“状态防火墙”，这是一个典型的错误

在客户端-服务器架构中，唯一可预先知道的端口是目标端口，因为客户端会选择一个临时端口1，除了一些极其罕见的例外，例如 DHCP。

从防火墙的角度来看，从防火墙驱逐的每个数据包都具有 NEW 状态，尤其是在 TCP 连接中。2

首先让我们看看我们有什么

IPT=/sbin/iptables
$IPT -F
$IPT -X
$IPT -t nat -F
$IPT -t nat -X
$IPT -t mangle -F
$IPT -t mangle -X
$IPT -P INPUT DROP
$IPT -P FORWARD DROP
$IPT -P OUTPUT DROP

# Excellent!! because always we need to accept this kind of states because
# always are response packets, remember we can be client or server
$IPT -A INPUT -m state --STATE ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -m state --STATE ESTABLISHED,RELATED -j ACCEPT

# Allow All for SSH
# this accept ssh connections from outside, and the response for this input
# is a outgoing packet with the state ESTABLISHED. (four lines above)
$IPT -A INPUT -i eth0 -p tcp --dport 22 -j ACCEPT

# this rule are meaningless because you never start a ssh connection from
# source port 22, this because the source ports are choose randomly
$IPT -A OUTPUT -o eth0 -p tcp --sport 22 -j ACCEPT

# this one let start a ssh connection from within to the outside and the response
# enter in state ESTABLISHED, 13 lines above
$IPT -A OUTPUT -o eth0 -p tcp --dport 22 -j ACCEPT

# Allow all for HTTP / HTTPS
# http servers are very basic if we think on client-server, they only respond a
# client request, except if some web software try to establish a network connection
# to the outside, for this block the only rule with meaning is the first, the rest are
# meaningless
$IPT -A INPUT -i eth0 -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
$IPT -A OUTPUT -o eth0 -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT
$IPT -A OUTPUT -o eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
$IPT -A INPUT -i eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

# Allow loopback traffic
# this are obligatory rules avoiding the firewall block himself
$IPT -A INPUT -i lo -j ACCEPT
$IPT -A OUTPUT -o lo -j ACCEPT

# Allow to be pinged ( Outside => srv )
# always the interpretation depends from the point of view
# with this rules you can accept ping request from outside and despond the request
# but you cannot ping from inside to outside because in that scenario you send the request (OUTPUT)
# and receive a reply from outside (INPUT) 
$IPT -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
$IPT -A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT


# Allow outgoing DNS connections
# this allow send dns queries to the DNS server that you have registered in the file
# /etc/resolv.conf
$IPT -A OUTPUT -p udp -o eth0 --dport 53 -j ACCEPT
# this one are meaningless because the response from the DNS server is ESTABLISHED and is 
# accepted in the very beginning in the firewall 
$IPT -A INPUT -p udp -i eth0 --sport 53 -j ACCEPT

# Apt-get
# AFAIK apt use http or ftp, they can use https but is less common
# the specification of a range on source port are meaningless
$IPT -A OUTPUT -p tcp --dport 80 --sport 32786:61000 -j ACCEPT
$IPT -A INPUT -p tcp --dport 80 --sport 32786:61000 -j ACCEPT
$IPT -A OUTPUT -p tcp --dport 32786:61000 --sport 80 -j ACCEPT
$IPT -A INPUT -p tcp --dport 32786:61000 --sport 80 -j ACCEPT

# SMTP Outgoing
# I don't known why you start adding more criteria without meaning 
# maybe you start surfing on the net and starting copy&paste code without see what you are doing
# always when yo need to learn something go to the root, or in this case to www.netfilter.org
$IPT -A OUTPUT -p tcp --sport 1024:65535 -d 0/0 --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT
$IPT -A INPUT -p tcp -s 0/0 --sport 25 --dport 1024:65535 -m state --state ESTABLISHED-j ACCEPT


# the rules below are.... copy&paste from somewhere

# Prevent DoS
#$IPT -A INPUT -p tcp --dport 80 -m limit --limit 60/minute --limit-burst 150 -j ACCEPT
$IPT -A INPUT -p tcp --dport 80 -m connlimit --connlimit-above 100 --connlimit-mask 32     -j REJECT --reject-with tcp-reset
#
# Log dropped packets
$IPT -N LOGGING
$IPT -A INPUT -j LOGGING
$IPT -A LOGGING -m limit --limit 2/min -j LOG --log-prefix "IPTables Packet Dropped: "     --log-level 7
$IPT -A LOGGING -j DROP

所以对我来说，你需要这个防火墙

IPT=/sbin/iptables
$IPT -F
$IPT -X
$IPT -t nat -F
$IPT -t nat -X
$IPT -t mangle -F
$IPT -t mangle -X
$IPT -P INPUT DROP
$IPT -P FORWARD DROP
$IPT -P OUTPUT DROP

# accept a priori all the responses
$IPT -A INPUT -m state --STATE ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -m state --STATE ESTABLISHED,RELATED -j ACCEPT

# Allow All for SSH 
# allow ssh connections from outside to inside
$IPT -A INPUT -i eth0 -p tcp --dport 22 -j ACCEPT

# allow ssh connections from inside to outside
$IPT -A OUTPUT -o eth0 -p tcp --dport 22 -j ACCEPT

# Allow all for HTTP / HTTPS
$IPT -A INPUT -i eth0 -p tcp --dport 80 -j ACCEPT
$IPT -A INPUT -i eth0 -p tcp --dport 443 -j ACCEPT

# Allow loopback traffic
$IPT -A INPUT -i lo -j ACCEPT
$IPT -A OUTPUT -o lo -j ACCEPT

# Allow to be pinged ( Outside => srv )
$IPT -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
$IPT -A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT
# from srv to outside
$IPT -A INPUT -p icmp --icmp-type echo-reply -j ACCEPT
$IPT -A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT

# Allow outgoing DNS connections
$IPT -A OUTPUT -p udp -o eth0 --dport 53 -j ACCEPT

# Apt-get
$IPT -A OUTPUT -p tcp --dport 80 -j ACCEPT
$IPT -A OUTPUT -p tcp --dport 21 -j ACCEPT

# SMTP Outgoing
$IPT -A OUTPUT -p tcp --dport 25 -j ACCEPT

希望对您有所帮助。抱歉，我的英语不是我的母语。

Answer