GSEC · Question #63
The TTL can be found in which protocol header?
The correct answer is B. It is found in byte 8 of the IP header.. The IPv4 TTL field sits at byte offset 8 in the IP header, where it controls how many hops a packet may traverse.
Question
The TTL can be found in which protocol header?
Options
- AIt is found in byte 8 of the ICMP header.
- BIt is found in byte 8 of the IP header.
- CIt is found in byte 8 of the TCP header.
- DIt is found in byte 8 of the DNS header.
How the community answered
(21 responses)- A5% (1)
- B81% (17)
- C10% (2)
- D5% (1)
Why each option
The IPv4 TTL field sits at byte offset 8 in the IP header, where it controls how many hops a packet may traverse.
The ICMP header has no TTL field; ICMP messages are encapsulated in IP packets and rely on the IP header for TTL.
In the IPv4 header defined by RFC 791, the first 8 bytes cover Version/IHL, DSCP/ECN, Total Length, Identification, Flags, and Fragment Offset, placing the TTL field at byte offset 8. Each forwarding router decrements TTL by one and discards the packet when it reaches zero, preventing routing loops.
The TCP header contains no TTL field; TTL is a Layer 3 concept managed entirely by the IP header.
DNS resource records carry a TTL value inside the DNS message payload, not in a transport or network header at byte offset 8.
Concept tested: IPv4 header structure and TTL field location
Source: https://datatracker.ietf.org/doc/html/rfc791
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