Cisco Certified Internetwork Expert (CCIE) Practice Test

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Boost your skills for the CCIE Exam. Enhance your knowledge with interactive multiple-choice questions, including hints and explanations. Prepare effectively for your certification exam!

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Which two statements are true about the TTL value in an IPv4 header?

Its maximum value is 255
It is a 4-bit value
It can be used for traceroute operations
When it reaches 0, it generates an ICMP Type 11 message

The correct answer is: It can be used for traceroute operations

The statement that the Time to Live (TTL) value in an IPv4 header can be used for traceroute operations is accurate. In the case of the traceroute utility, each packet is sent with a TTL value that is incremented with each successive packet. This process allows the packets to be routed through a sequence of network devices (routers), and each router decrements the TTL by one. When the TTL reaches zero, the router drops the packet and sends back an ICMP Type 11 message to the source. This message indicates that the TTL has expired and provides the source with the IP address of the router that dropped the packet. This mechanism allows the traceroute command to map out the path packets take to a destination IP, revealing each hop along the way. The other statements about the TTL value do not hold true. The maximum value of TTL is indeed 255, but it is important to note that TTL is actually an 8-bit field within the IPv4 header. Therefore, while there can be confusion regarding its bit size and operations, the correct understanding of TTL is critical for network diagnostics and understanding routing behaviors.