1. Use route command to add
//Routes added to hosts
[root@localhost ~]# route add -host 8.8.8.8 dev ens3
[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.25.8.250 0.0.0.0 UG 100 0 0 ens3
8.8.8.8 0.0.0.0 255.255.255.255 UH 0 0 0 ens3
172.25.0.0 0.0.0.0 255.255.0.0 U 100 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
[root@localhost ~]# route add -host 8.8.8.8 gw 8.8.8.8
[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.25.8.250 0.0.0.0 UG 100 0 0 ens3
8.8.8.8 8.8.8.8 255.255.255.255 UGH 0 0 0 ens3
8.8.8.8 0.0.0.0 255.255.255.255 UH 0 0 0 ens3
172.25.0.0 0.0.0.0 255.255.0.0 U 100 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0//Routes added to the network (why)
route add –net 11.11.1.11 netmask 255.255.255.0 dev eth0
route add –net 11.11.1.11 netmask 255.255.255.0 gw 11.11.1.1
route add –net 11.11.1.0/24 dev eth1//Add default gateway
[root@localhost ~]# route add default gw 172.25.8.250
[root@localhost ~]# route add default gw 172.25.8.251
[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.25.8.251 0.0.0.0 UG 0 0 0 ens3
0.0.0.0 172.25.8.250 0.0.0.0 UG 0 0 0 ens3
0.0.0.0 172.25.8.250 0.0.0.0 UG 100 0 0 ens3
8.8.8.8 8.8.8.8 255.255.255.255 UGH 0 0 0 ens3
8.8.8.8 0.0.0.0 255.255.255.255 UH 0 0 0 ens3
172.25.0.0 0.0.0.0 255.255.0.0 U 100 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0//Delete route
[root@localhost ~]# route del -host 8.8.8.8 dev ens3
[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.25.8.251 0.0.0.0 UG 0 0 0 ens3
0.0.0.0 172.25.8.250 0.0.0.0 UG 0 0 0 ens3
0.0.0.0 172.25.8.250 0.0.0.0 UG 100 0 0 ens3
172.25.0.0 0.0.0.0 255.255.0.0 U 100 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0//After the machine restarts or the network card restarts, the route fails
[root@localhost ~]# systemctl restart network
[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.25.8.250 0.0.0.0 UG 100 0 0 ens3
172.25.0.0 0.0.0.0 255.255.0.0 U 100 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr02. Use ip command to add and delete routes
[root@localhost ~]# ip route add default via 172.25.8.251 dev ens3
[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.25.8.251 0.0.0.0 UG 0 0 0 ens3
0.0.0.0 172.25.8.250 0.0.0.0 UG 100 0 0 ens3
172.25.0.0 0.0.0.0 255.255.0.0 U 100 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
[root@localhost ~]# ip route add 172.16.1.0/24 via 172.25.8.251 dev ens3
[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.25.8.251 0.0.0.0 UG 0 0 0 ens3
0.0.0.0 172.25.8.250 0.0.0.0 UG 100 0 0 ens3
172.16.1.0 172.25.8.251 255.255.255.0 UG 0 0 0 ens3
172.25.0.0 0.0.0.0 255.255.0.0 U 100 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
3. How to set permanent route under linux
1) Added to the end of / etc/sysconfig/network is globally valid. (effective method)
Gateway = GW IP or gateway = GW dev
2) Add routes under / etc / sysconfig / network script / route interface (one file for each interface, if not, only routes for that interface can be added)
For example, add a default gateway to eth0:
vim /etc/sysconfig/network-scripts/ifcfg-eth0
#Add the following (you can omit dev eth0)
GATEWAY=X.X.X.X
#After saving and exiting
service network restart or systemctl restart network.