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Practical BGP by Sangli Srihari, Russ White, Danny McPherson

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Forcing Symmetric Entry and Exit Points

Because BGP and other routing protocols primarily focus on the next hop toward a destination at each router or hop rather than a complete path, asymmetric routing is the normal, accepted behavior when dual homing to one or two service providers. However, there are situations where asymmetric traffic flow isn't desirable, such as the network connections illustrated in Figure 2.21.

Figure 2.21. Forcing symmetric routing.

As you can see, there are a pair of firewalls, one behind each router that connects to an Internet service provider. Since firewalls generally inspect packets based on the flow to which the ...

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