最近在尝试搭建一个校内的 csgo 服务器。但是用来跑 csgo 服务器的机子拿不到公网访问，恰巧手头又有一个树莓派有公网 ip 可以访问，于是尝试进行端口映射使服务器暴露出来。
先说说 socat 的一些优点：配置简单，性能好，各大发行版均可以用包管理器进行安装。
相比于 iptables 动辄一大串的命令参数，socat 的启动方式非常简单：
socat tcp4-listen:27015,reuseaddr,fork tcp4:192.168.xx.xx:27015&
socat udp4-listen:27015,reuseaddr,fork udp4:192.168.xx.xx:27015&
两行语句，就完成了端口映射,此时已经可以访问此服务器。
另外，socat 相比 iptables 还有一些优点：支持 6to4 和 4to6 转发，而 iptables 不支持。
简单帖个 socat -h 的输出
socat by Gerhard Rieger and contributors - see www.dest-unreach.org
Usage:
socat [options] <bi-address> <bi-address>
options:
-V print version and feature information to stdout, and exit
-h|-? print a help text describing command line options and addresses
-hh like -h, plus a list of all common address option names
-hhh like -hh, plus a list of all available address option names
-d[ddd] increase verbosity (use up to 4 times; 2 are recommended)
-D analyze file descriptors before loop
-ly[facility] log to syslog, using facility (default is daemon)
-lf<logfile> log to file
-ls log to stderr (default if no other log)
-lm[facility] mixed log mode (stderr during initialization, then syslog)
-lp<progname> set the program name used for logging
-lu use microseconds for logging timestamps
-lh add hostname to log messages
-v verbose text dump of data traffic
-x verbose hexadecimal dump of data traffic
-r <file> raw dump of data flowing from left to right
-R <file> raw dump of data flowing from right to left
-b<size_t> set data buffer size (8192)
-s sloppy (continue on error)
-t<timeout> wait seconds before closing second channel
-T<timeout> total inactivity timeout in seconds
-u unidirectional mode (left to right)
-U unidirectional mode (right to left)
-g do not check option groups
-L <lockfile> try to obtain lock, or fail
-W <lockfile> try to obtain lock, or wait
-4 prefer IPv4 if version is not explicitly specified
-6 prefer IPv6 if version is not explicitly specified
bi-address:
pipe[,<opts>] groups=FD,FIFO
<single-address>!!<single-address>
<single-address>
single-address:
<address-head>[,<opts>]
address-head:
abstract-client:<filename> groups=FD,SOCKET,RETRY,UNIX
abstract-connect:<filename> groups=FD,SOCKET,RETRY,UNIX
abstract-listen:<filename> groups=FD,SOCKET,LISTEN,CHILD,RETRY,UNIX
abstract-recv:<filename> groups=FD,SOCKET,RETRY,UNIX
abstract-recvfrom:<filename> groups=FD,SOCKET,CHILD,RETRY,UNIX
abstract-sendto:<filename> groups=FD,SOCKET,RETRY,UNIX
create:<filename> groups=FD,REG,NAMED
exec:<command-line> groups=FD,FIFO,SOCKET,EXEC,FORK,TERMIOS,PTY,PARENT,UNIX
fd:<num> groups=FD,FIFO,CHR,BLK,REG,SOCKET,TERMIOS,UNIX,IP4,IP6,UDP,TCP,SCTP
gopen:<filename> groups=FD,FIFO,CHR,BLK,REG,SOCKET,NAMED,OPEN,TERMIOS,UNIX
interface:<interface> groups=FD,SOCKET
ip-datagram:<host>:<protocol> groups=FD,SOCKET,RANGE,IP4,IP6
ip-recv:<protocol> groups=FD,SOCKET,RANGE,IP4,IP6
ip-recvfrom:<protocol> groups=FD,SOCKET,CHILD,RANGE,IP4,IP6
ip-sendto:<host>:<protocol> groups=FD,SOCKET,IP4,IP6
ip4-datagram:<host>:<protocol> groups=FD,SOCKET,RANGE,IP4
ip4-recv:<protocol> groups=FD,SOCKET,RANGE,IP4
ip4-recvfrom:<protocol> groups=FD,SOCKET,CHILD,RANGE,IP4
ip4-sendto:<host>:<protocol> groups=FD,SOCKET,IP4
ip6-datagram:<host>:<protocol> groups=FD,SOCKET,RANGE,IP6
ip6-recv:<protocol> groups=FD,SOCKET,RANGE,IP6
ip6-recvfrom:<protocol> groups=FD,SOCKET,CHILD,RANGE,IP6
ip6-sendto:<host>:<protocol> groups=FD,SOCKET,IP6
open:<filename> groups=FD,FIFO,CHR,BLK,REG,NAMED,OPEN,TERMIOS
openssl:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,IP6,TCP,OPENSSL
openssl-dtls-client:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,IP6,UDP,OPENSSL
openssl-dtls-server:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP4,IP6,UDP,OPENSSL
openssl-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP4,IP6,TCP,OPENSSL
pipe:<filename> groups=FD,FIFO,NAMED,OPEN
proxy:<proxy-server>:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,IP6,TCP,HTTP
pty groups=FD,NAMED,TERMIOS,PTY
sctp-connect:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,IP6,SCTP
sctp-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP4,IP6,SCTP
sctp4-connect:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,SCTP
sctp4-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP4,SCTP
sctp6-connect:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP6,SCTP
sctp6-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP6,SCTP
socket-connect:<domain>:<protocol>:<remote-address> groups=FD,SOCKET,CHILD,RETRY
socket-datagram:<domain>:<type>:<protocol>:<remote-address> groups=FD,SOCKET,RANGE
socket-listen:<domain>:<protocol>:<local-address> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE
socket-recv:<domain>:<type>:<protocol>:<local-address> groups=FD,SOCKET,RANGE
socket-recvfrom:<domain>:<type>:<protocol>:<local-address> groups=FD,SOCKET,CHILD,RANGE
socket-sendto:<domain>:<type>:<protocol>:<remote-address> groups=FD,SOCKET
socks4:<socks-server>:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,IP6,TCP,SOCKS4
socks4a:<socks-server>:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,IP6,TCP,SOCKS4
stderr groups=FD,FIFO,CHR,BLK,REG,SOCKET,TERMIOS,UNIX,IP4,IP6,UDP,TCP,SCTP
stdin groups=FD,FIFO,CHR,BLK,REG,SOCKET,TERMIOS,UNIX,IP4,IP6,UDP,TCP,SCTP
stdio groups=FD,FIFO,CHR,BLK,REG,SOCKET,TERMIOS,UNIX,IP4,IP6,UDP,TCP,SCTP
stdout groups=FD,FIFO,CHR,BLK,REG,SOCKET,TERMIOS,UNIX,IP4,IP6,UDP,TCP,SCTP
system:<shell-command> groups=FD,FIFO,SOCKET,EXEC,FORK,TERMIOS,PTY,PARENT,UNIX
tcp-connect:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,IP6,TCP
tcp-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP4,IP6,TCP
tcp4-connect:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP4,TCP
tcp4-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP4,TCP
tcp6-connect:<host>:<port> groups=FD,SOCKET,CHILD,RETRY,IP6,TCP
tcp6-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY,RANGE,IP6,TCP
tun[:<ip-addr>/<bits>] groups=FD,CHR,NAMED,OPEN,INTERFACE
udp-connect:<host>:<port> groups=FD,SOCKET,IP4,IP6,UDP
udp-datagram:<host>:<port> groups=FD,SOCKET,RANGE,IP4,IP6,UDP
udp-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,UDP
udp-recv:<port> groups=FD,SOCKET,RANGE,IP4,IP6,UDP
udp-recvfrom:<port> groups=FD,SOCKET,CHILD,RANGE,IP4,IP6,UDP
udp-sendto:<host>:<port> groups=FD,SOCKET,IP4,IP6,UDP
udp4-connect:<host>:<port> groups=FD,SOCKET,IP4,UDP
udp4-datagram:<host>:<port> groups=FD,SOCKET,RANGE,IP4,UDP
udp4-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RANGE,IP4,UDP
udp4-recv:<port> groups=FD,SOCKET,RANGE,IP4,UDP
udp4-recvfrom:<port> groups=FD,SOCKET,CHILD,RANGE,IP4,UDP
udp4-sendto:<host>:<port> groups=FD,SOCKET,IP4,UDP
udp6-connect:<host>:<port> groups=FD,SOCKET,IP6,UDP
udp6-datagram:<host>:<port> groups=FD,SOCKET,RANGE,IP6,UDP
udp6-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RANGE,IP6,UDP
udp6-recv:<port> groups=FD,SOCKET,RANGE,IP6,UDP
udp6-recvfrom:<port> groups=FD,SOCKET,CHILD,RANGE,IP6,UDP
udp6-sendto:<host>:<port> groups=FD,SOCKET,IP6,UDP
unix-client:<filename> groups=FD,SOCKET,NAMED,RETRY,UNIX
unix-connect:<filename> groups=FD,SOCKET,NAMED,RETRY,UNIX
unix-listen:<filename> groups=FD,SOCKET,NAMED,LISTEN,CHILD,RETRY,UNIX
unix-recv:<filename> groups=FD,SOCKET,NAMED,RETRY,UNIX
unix-recvfrom:<filename> groups=FD,SOCKET,NAMED,CHILD,RETRY,UNIX
unix-sendto:<filename> groups=FD,SOCKET,NAMED,RETRY,UNIX
vsock-connect:<cid>:<port> groups=FD,SOCKET,CHILD,RETRY
vsock-listen:<port> groups=FD,SOCKET,LISTEN,CHILD,RETRY