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ccna 200 301 bookshelves target for wall.. They are encapsulated in IP packets. Some common events and messages associated with ICMP are described next. . DestinationUnreachable If the router can no longer forward IP packets,it uses ICMP to return a message to the sender host informing it of the situation. Take Figure 4.9 as an example, which shows that the E0 interface of the Lab_B router is down.Lab_B's E0 is down, and Host A tries to communicate with Host B. What happens then?Figure 4.9 Remote Router Sends ICMP Error Message to Sending Host Host A sends a packet with host B as the destination, and the Lab_B router sends a packet to the sending host (alsois host A in this example) returns an ICMP destination unreachable message. BufferFull/SourceQuence If the router receives incoming datathe cache is full, it sends this message using ICMP until congestion is relieved.Hops/TimeExceeded Each packet is specified to be able to traverse a certain number ofof routers, and this number is called the hop count. If the number of routers traversed by the packet before it reaches its destination reachesthis hop limit, then the last router to receive the packet drops it. The router that dropped the packet then uses ICMP to send an "obituary" message to the sender host, telling it that the packet has been dropped due to the hop limit.The Ping packet network probe (Ping) uses ICMP Echo Request and Echo Response