网关是网络中的路由器，其作为访问其他网络的接入点；当IP地址与路由表中的地址不匹配时，便使用默认网关。
在Linux中使用netstat -r 或 route -n来查看默认网关。
What is default gateway? How can we find it in Linux?
A gateway is a router on a TCP/IP network that serves as an access point to another network. A default gateway is the router on the network that the network software uses when an IP address does not match any other routes in the routing table.
netstat –r –n or route –n.