路由条目类型
- 主机路由：目标地址为单个IP。
- 网络路由：目标地址为IP网络。
- 默认路由：目标为任意主机，0.0.0.0/0.0.0.0。
用法，查看帮助
# man route
-v, --verbose：be verbose
-n, --numeric：don't resolve names
-ee, --extend：display other/more information
add：add a new route.
del：delete a route.
-net：the target is a network.
-host：the target is a host.
netmask|NM：when adding a network route, the netmask to be used.
gw|GW：route packets via a gateway.
dev：If force the route to be associated with the specified device, as the kernel will try to determine the device on its own. 可以不指定，内核会自己判断用哪块网卡
添加路由
# route add -net 0.0.0.0/0.0.0.0 gw 192.168.10.1
# route add default gw 192.168.10.1
# route add -net 192.56.76.0 netmask 255.255.255.0 dev eth0
adds a route to the local network 192.56.76.x via "eth0". The word "dev" can be omitted here.
删除路由
# route del default
deletes the current default route, which is labeled "default" or 0.0.0.0 in the destination field of the current routing table.
# route del -net 10.0.0.0/8 gw 192.168.10.1
查看路由表
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.1.254 0.0.0.0 UG 0 0 0 eth0
0.0.0.0 122.14.206.1 0.0.0.0 UG 0 0 0 eth1
122.14.206.0 0.0.0.0 255.255.254.0 U 0 0 0 eth1
192.168.0.0 0.0.0.0 255.255.240.0 U 0 0 0 eth0
各字段含义
Destination：The destination network or destination host. 目标网络或主机。
Gateway：The gateway address or '*' if none set. 网关地址，如果不指定则默认为*。
Genmask：The netmask for the destination net; '255.255.255.255' for a host destination and '0.0.0.0' for the default route. 目标网络的掩码，默认路由的掩码为0.0.0.0。
Flags：Possible flags include
U (route is up)：该路由是启动的。
H (target is a host)：目标是一个主机。
G (use gateway)：使用外部网关。
R (reinstate route for dynamic routing)：使用动态路由时，恢复路由。
D (dynamically installed by daemon or redirect)：
M (modified from routing daemon or redirect)
A (installed by addrconf)
C (cache entry)
! (reject route)：该路由被拒绝，用来抵挡不安全的网域。
Metric：The 'distance' to the target (usually counted in hops). It is not used by recent kernels, but may be needed by routing daemons. 距离、跳数。
Ref：Number of references to this route. (Not used in the Linux kernel.)
Use：Count of lookups for the route. Depending on the use of -F and -C this will be either route cache misses (-F) or hits (-C).
Iface：Interface to which packets for this route will be sent.
另外，路由表是有顺序的，从上到下匹配。如果在eth0和eth1上分别添加一条一样的路由，比如这样：
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
这时，数据包都会从eth0传出去。