深入理解Netscaler INat
http://blog.51cto.com/caojin/1898173
Netscaler的INat主要是用作基于目的地址的转换，将client访问的公网IP通过Netscaler转换成服务器的私网IP，与DNAT作用类似。由于Netscaler默认的工作机制就是同时做源IP：【源端口】+目的IP：【目的端口】的转换，也就是说它默认执行了NAPT（端口映射）但有不完全等同与NAPT。NAPT只替换目的IP和端口，而Netscaler默认是全部替换的。
测试环境：
SNIP：10.110.110.121
10.110.140.151
10.110.140.152
MIP： 10.110.140.153
VIP：111.1.1.1
Client：10.110.110.146
Server VIP：10.110.140.150
Server：10.110.110.130
配置方法:
> add inat <name> <public ip> <private ip>(private ip不能是Netscaler所属的IP包括VIP）
-ftp ( ENABLED | DISABLED )
-mode STATELESS
-proxyIP <ip_addr|ipv6_addr>
-tcpproxy ( ENABLED | DISABLED )
-td <positive_integer>
-tftp ( ENABLED | DISABLED )
-usip ( ON | OFF )
-usnip ( ON | OFF )
When the appliance forwards a packet to a server, the source IP address assigned to the
packet is determined as follows:
-
If use subnet IP (USNIP) mode is enabled and use source IP (USIP) mode is disabled,
the NetScaler uses a subnet IP address (SNIP) as the source IP address.
-
If USNIP mode is disabled and USIP mode is disabled, the NetScaler uses a mapped IP
address (MIP) as the source IP address.
-
If USIP mode is enabled, and USNIP mode is disabled the NetScaler uses the client IP
(CIP) address as the source IP address.
-
If both USIP and USNIP modes are enabled, USIP mode takes precedence.
-
You can also configure the NetScaler to use a unique IP address as the source IP
address, by setting the proxyIP parameter.
-
If none of the above modes is enabled and a unique IP address has not been
specified, the NetScaler attempts to use a MIP as the source IP address.
-
If both USIP and USNIP modes are enabled and a unique IP address has been
specified, the order of precedence is as follows: USIP-unique IP-USNIP-MIP-Error.
To protect the NetScaler from DoS attacks, you can enable TCP proxy. However, if other
protection mechanisms are used in your network, you may want to disable them.
如果启用了proxy ip，那么与服务器连接就只用一个SNIP，与静态DNAT类似
如果关闭proxy ip，Netscaler将采用轮训的方式，用与私网目的IP一个网段的SNIP来连接服务器，类似动态DNAT
只打开USIP时，Netscaler会用client的源ip来与后台私网连接（由于测试环境没有去client的路由因此没有完成TCP连接）
同时打开USIP和USNIP时，由于USIP的优先级高于USNIP，Netscaler会用client的源ip来与后台私网连接（由于测试环境没有去client的路由因此没有完成TCP连接）
关闭USIP和USNIP后，Netscaler会用MIP来与后台连接
关闭USIP和USNIP，但选择了Proxy IP后，被选择的SNIP优先高于MIP，会用它与后台服务器连接
不管是用USIP还是USNIP，启用了TCP proxy后Netscaler都会用client源IP来与后台连接，tcp proxy可以保护Netscaler抵抗DOS攻击
Mode中的stateless只能应用与IPV4-IPV6的转换
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