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Mohamed G. Gouda					CS 356
Spring 2018						Exercise 8
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When a router R receives an ICMP packet q, how can R check that
packet q is indeed an ICMP packet?

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Solution
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Packet q has an IP header. This header has a field that specifies 
the upper layer protocol (UDP, TCP, or ICMP) of packet q. If this 
field specifies ICMP, then router R concludes that the received
packet q is indeed an ICMP packet.