Network Troubleshooting

Correct Answer: ping

The 'ping' command is used to test the connectivity to a remote host. It sends a series of data packets to a specific IP address, and await a response. If received, it signifies that the network pathway to the remote host exists and is operational. The 'nslookup' command, on the other hand, is used to obtain information about Internet servers using domain name system (DNS) queries, not to test connectivity. 'netstat' is used for displaying network connections, both incoming and outgoing, routing tables, and a number of network interface and network protocol statistics and 'ifconfig' is typically used to view or change network configurations on a system, not to test connection to a remote host.

Correct Answer: ipconfig /flushdns

The command to flush the DNS cache on a Windows machine is 'ipconfig /flushdns'. This command sends a request to the DNS server to empty the cache of IP addresses and their corresponding DNS names. The other commands given do not perform this operation. 'netstat -r' displays the routing table, 'ping -a' does a reverse name lookup, and 'nslookup' queries the DNS to obtain domain name or IP address mapping or any other specific DNS record.

Correct Answer: To limit the number of routers an IP packet can pass through before being discarded.

The purpose of the TTL (Time to Live) field in the IP header is to limit the number of routers an IP packet can pass through before being discarded. This is to prevent data packets from circulating indefinitely within a network in the case of routing loops. Each time the packet passes through a router, the TTL value is decremented by one. When the TTL value reaches zero, the packet is discarded. This explanation makes the other answers incorrect. Answer about specifying the size of the IP packet in bytes is incorrect because that is the job of another field in IP header, not the TTL. The answer about indicating the order in fragmented IP packets should be reassembled is incorrect because again, there is another field in IP header responsible for that- fragmentation offset field. The TTL field does not specify the type of data carried in the IP packet, that is the work of protocol field. These reasons make 'to limit the number of routers an IP packet can pass through before being discarded' the best answer in this question.