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- Step 1: the destination address is checked against the networks present in the routing table to see if it finds a match.
- Step 2: if several records satisfy the requirement of step 1, the "narrowest route" is selected, i.e. the entry having the maximum netmask value is selected. For example, mask /24 is narrower than /8.
- Step 3: if at step 2 there are several routing table entries with the same network masks, the Distance parameter is compared. The lower the value of this parameter, the higher the priority of the route.
- Step 4: if at step 3 there are several entries in the routing table with the same Distance value, the metrics are compared. The lower the metric value, the higher the priority of the route.
- Step 5: if there is no entry in the routing table that meets the requirements of step 1 and there is no default route, the packet is dropped.
Routing
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table management examples
Let's look at the some examples of the routing table management in various scenarios (Figure 6a-c).
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- Step 1a: PC1 generates a packet with the destination IP address of PC2 and transfers it for processing to the L2 layer of the network interface.
- Step 1b: The L2 layer of the PC1's network interface verifies that the destination belongs to the source networkto which MAC address is mapped the destination IP address by checking the switching table (when the first frame is transmitted towards a destination, the ARP protocol is used for determining the MAC address). Since PC1 and PC2 belong to the same network, the the PC2's network interface MAC address is set in the Ethernet header. The generated frame is sent to Switch1.
- Step 1c: The switch transmits the frame to PC2 frame according to the switching table.
Data are is transmitted using switching technologies within the same network using switching technologies, router R1 does not participate in this process.
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