TTL (Time To Live)
TTL limits how many hops a packet can traverse to prevent infinite routing loops.
Updated: 2026-03-05
Definition
TTL is a field in IP headers decreased by 1 at each router hop.
When TTL reaches 0, the packet is dropped and an ICMP time-exceeded message can be sent.
Key points
- Decreases at each hop
- Prevents endless loops
- Used by traceroute
Common mistakes
- Confusing TTL with DNS TTL (different concepts).
- Ignoring TTL-related drops during troubleshooting.
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