Explain the outcome of Step 5. That is, explain why the ping issued by PC3 has the effect that the ping commands from PC1 to PC3 (in step4) are successful. Compare the outcome with the outcome in Step 2.
What will be an ideal response?
```
[root@PC3 lab6]# ping -c 1 10.0.1.11
PING 10.0.1.11 (10.0.1.11) 56(84) bytes of data.
64 bytes from 10.0.1.11: icmp_seq=1 ttl=64 time=1.84 ms
--- 10.0.1.11 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 1.842/1.842/1.842/0.000 ms
```
We notice that the time required for ping requests to be successful is higher for PC1 to PC2 as compared
to PC1 to PC3.
When PC2 is connected to the hub of PC4, Router3 does not know that PC2 has moved, hence it does not
forward the ICMP echo request packet and the packet does not reach PC2. Eventually since the MAC
forwarding entry for PC2 is not refreshed at Router2 and Router3, the entry is deleted. When the entry is
deleted the next ICMP echo request from PC1 is flooded on all ports, thus reaching PC2. When PC2
responds, all bridges update their MAC forwarding table using the source MAC address of PC2.
When PC3 is connected to the hub of PC4, Router3 does not know that PC3 has moved, hence it does not
forward the ICMP echo request packet and the packet does not reach PC3. However when a ping command is issued by PC3 for PC1, the MAC forwarding tables of Router3 is updated, while that of router 2 and Router1 is refreshed. Thus the ICMP echo request packets are forwarded by Router3 and PC3 responds. Thus the ping command from PC3 (when issued before the time-out of the MAC entries) serves as a trigger to enable quicker success of the PC1 ping command.
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