1. 此例中,得到协议是IP后, IP 先在IP header上运行CRC, 然后检测destination IP address.
注意1: IP仅仅是完成部分CRC, 并非像Data Link Layer, IP只是检查header
注意2: 当ping不通时候, 并不是说packet没有到达destination host, 而是一个remote router 没有找到一条回到originating host’s network的route. 所以说, packet是在回路上掉了, 而不是去路上掉了.
注意3: 当packet is lost on the way back to the originating host—request timed out
当route is not in the routing table on the way to the destination device—destination unreachable message
2. 如此一来, packet 知道了怎么达到172.16.10.0, 这是Ethernet 0 的exit interface, 就这样packet被switch到了interface Ethernet 0
3. Router, 也就是LAB_A检查ARP cache以确定IP是172.16.10.2的主机hostA的硬件地址是否已经解析.
4. 这样hostA的硬件地址is already cached from the originating trip to hostB, 于是硬件地址和packet被传往Data Link Layer.
5. Data Link Layer再次frame
6. 发到physical layer one bit /time
7. Destination host 收到frame, 先CRC, 再检测destination hardware address, 最后查找ether-type field
8. Packet 传给了Network layer的IP, IP检测protocol field, 并且把payload发给ICMP, 然后ICMP确定这个packet 是一个ICMP echo reply
9. ICMP acknowledges, 它收到了一个reply.
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