When configuring two gateways on Linux, usually only one gateway will be used for the default route unless you use a specific routing policy.
By default, Linux systems can only have one default route, which is used to send all outbound traffic. When you configure two gateways, the operating system selects one as the default route and ignores the other. This means that only one gateway will be used for all outbound traffic, and the other gateway will be ignored.
This may be the reason why only one gateway is available. If you want to use two gateways at the same time, you need to use specific routing policies and rules.
Here's one way to implement two gateways at the same time:
创建两个路由表，每个路由表对应一个网关。
创建路由表1（例如，gateway1）：
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sudo echo “1 gateway1” >> /etc/iproute2/rt_tables
创建路由表2（例如，gateway2）：
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sudo echo "2 gateway2" >> /etc/iproute2/rt_tables
Configure routing rules for each gateway.
Set routing rules for gateway 1 (for example, 192.168.1.1):
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sudo ip route add 192.168.1.0/24 dev eth0 table gateway1
sudo ip route add default via 192.168.1.1 table gateway1
针对网关2（例如，192.168.2.1）设置路由规则：
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sudo ip route add 192.168.2.0/24 dev eth1 table gateway2
sudo ip route add default via 192.168.2.1 table gateway2
Configure the main routing table rules.
Configure the main route table rules to choose which route table to use:
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sudo ip rule add from 192.168.1.0/24 table gateway1
sudo ip rule add from 192.168.2.0/24 table gateway2
启用IP转发。
请确保已经启用IP转发功能，以便正确转发流量：
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sudo sysctl net.ipv4.ip_forward=1
```
可以将上述命令添加到`/etc/sysctl.conf`文件中，以便在系统重启后保持设置。
完成上述步骤后，您应该能够同时使用两个网关进行通信。请注意，这种配置可能需要更复杂的网络架构和路由规划，并需要根据您的具体网络环境进行适当的配置。