很多时候可能存在如下的网络架构，小网的虚机（特别是版本构建机器）可能需要访问公司内部的服务，此时可以在双网卡机器上安装 squid 代理服务软件，然后在办公机器上配置代理服务器的大网 ip 和 squid 监听的端口作为代理，即可实现在办公网络访问小网，相应的，在小网虚机上配置代理服务器的小网 ip 和 squid 监听的端口作为代理，可以实现在小网访问办公网络。

但是，有时候在小网在访问办公网络并不能满足要求，可能需要连接外网下载开发包或工具等，此时需要为 squid 配置上层（parent）代理，即首先要解决双网卡机器自身访问外部网络的问题。

此时需要在 /etc/squid/squid.conf 中增加如下的配置，大致意思就是对于真正的外网访问转发至 cache_peer 定义的上一层代理服务器，而对于办公网络的访问直接直接由其自身进行转发：

# Parent proxy
acl to_localnet dst 10.0.0.0/8     # RFC1918 possible internal network
acl to_localnet dst 172.16.0.0/12  # RFC1918 possible internal network
acl to_localnet dst 192.168.0.0/16 # RFC1918 possible internal network
acl to_localnet dst fc00::/7       # RFC 4193 local private network range
acl to_localnet dst fe80::/10      # RFC 4291 link-local (directly plugged) machines

acl to_localdomain dstdomain .example.com

cache_peer proxy.example.com parent 80 0 default no-query no-digest
cache_peer_access proxy.example.com deny to_localnet
cache_peer_access proxy.example.com deny to_localdomain

never_direct deny to_localnet
never_direct deny to_localdomain
never_direct allow all

然后重启 squid 服务即可，具体的配置项的含义可以参考后文的参考链接。

附完整的 squid 配置文件内容如下：

#
# Recommended minimum configuration:
#

# Example rule allowing access from your local networks.
# Adapt to list your (internal) IP networks from where browsing
# should be allowed
acl localnet src 10.0.0.0/8 # RFC1918 possible internal network
acl localnet src 172.16.0.0/12  # RFC1918 possible internal network
acl localnet src 192.168.0.0/16 # RFC1918 possible internal network
acl localnet src fc00::/7       # RFC 4193 local private network range
acl localnet src fe80::/10      # RFC 4291 link-local (directly plugged) machines

acl Safe_ports port 22      # ssh
acl SSL_ports port 22       # ssh

acl Safe_ports port 873     # rsync
acl SSL_ports port 873      # rsync

acl SSL_ports port 9418     # git

acl SSL_ports port 443
acl Safe_ports port 80      # http
acl Safe_ports port 21      # ftp
acl Safe_ports port 443     # https
acl Safe_ports port 70      # gopher
acl Safe_ports port 210     # wais
acl Safe_ports port 1025-65535  # unregistered ports
acl Safe_ports port 280     # http-mgmt
acl Safe_ports port 488     # gss-http
acl Safe_ports port 591     # filemaker
acl Safe_ports port 777     # multiling http
acl CONNECT method CONNECT

#
# Recommended minimum Access Permission configuration:
#
# Deny requests to certain unsafe ports
http_access deny !Safe_ports

# Deny CONNECT to other than secure SSL ports
http_access deny CONNECT !SSL_ports

# Only allow cachemgr access from localhost
http_access allow localhost manager
http_access deny manager

# We strongly recommend the following be uncommented to protect innocent
# web applications running on the proxy server who think the only
# one who can access services on "localhost" is a local user
#http_access deny to_localhost

#
# INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
#

# Example rule allowing access from your local networks.
# Adapt localnet in the ACL section to list your (internal) IP networks
# from where browsing should be allowed
http_access allow localnet
http_access allow localhost

# And finally deny all other access to this proxy
http_access deny all

# Squid normally listens to port 3128
http_port 123456

# Parent proxy
acl to_localnet dst 10.0.0.0/8     # RFC1918 possible internal network
acl to_localnet dst 172.16.0.0/12  # RFC1918 possible internal network
acl to_localnet dst 192.168.0.0/16 # RFC1918 possible internal network
acl to_localnet dst fc00::/7       # RFC 4193 local private network range
acl to_localnet dst fe80::/10      # RFC 4291 link-local (directly plugged) machines

acl to_localdomain dstdomain .example.com

cache_peer proxy.example.com parent 80 0 default no-query no-digest
cache_peer_access proxy.example.com deny to_localnet
cache_peer_access proxy.example.com deny to_localdomain

never_direct deny to_localnet
never_direct deny to_localdomain
never_direct allow all

# Uncomment and adjust the following to add a disk cache directory.
#cache_dir ufs /var/spool/squid 100 16 256

# Leave coredumps in the first cache dir
coredump_dir /var/spool/squid

#
# Add any of your own refresh_pattern entries above these.
#
refresh_pattern ^ftp:       1440    20% 10080
refresh_pattern ^gopher:    1440    0%  1440
refresh_pattern -i (/cgi-bin/|\?) 0 0%  0
refresh_pattern .       0   20% 4320

参考文档

Configure Squid Proxy To Forward To A Parent Proxy

https://www.rootusers.com/configure-squid-proxy-to-forward-to-a-parent-proxy/

Squid configuration directive acl

http://www.squid-cache.org/Doc/config/acl/

Squid configuration directive cache_peer_domain

http://www.squid-cache.org/Doc/config/cache_peer_domain/

Squid configuration directive cache_peer_access

http://www.squid-cache.org/Doc/config/cache_peer_access/

最后修改于 2019-01-12