临时配置，重启网卡或系统后失效

route add -net 172.31.0.0  netmask 255.255.248.0 gw 10.33.42.10

永久配置

echo "172.31.0.0/21 via 10.33.42.10 dev em2" >> /etc/sysconfig/network-scripts/route-eno1

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