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Pinging with 2 Network Interfaces

Assuming that you have 2 network interfaces on you PC, one with IP 192.168.1.100 and one with IP 192.168.2.50, and that this is the routing table on your PC:

Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 192.168.1.1 192.168.1.100 10
169.254.0.0 255.255.255.0 192.168.2.1 192.168.2.50 5
10.10.10.0 255.255.255.0 192.168.2.1 192.168.2.50 100

a. When pinging 71.10.1.1, what interface will be used for the traffic? Why?
b. When pinging 169.254.0.10, what interface will be used for the traffic? Why?
c. When pinging 169.254.1.1, what interface will be used for the traffic? Why?
d. When pinging 10.10.10.1, what interface will be used for the traffic? Why?

Solution Preview

In order to understand how ping would choose between the network interfaces we need to understand the routing table
The example routing table is
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 192.168.1.1 192.168.1.100 10
169.254.0.0 255.255.255.0 192.168.2.1 192.168.2.50 5
10.10.10.0 255.255.255.0 192.168.2.1 192.168.2.50 100

Finding the route (See Route Determination Process [1])
The most suitable interface and gateway IP are determined using the following process:
The logical bitwise AND ...

Solution Summary

The solution covers with examples, how routing decision is made for any application (e.g., ping) by the router using the routing table. Specifically, this explains why certain routes are preferred over others when more than one network interface, and gateways are available.

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