Remember TTL
Full name: Time to Live
Memory aid: Traffic has a Travel Limit; cached records have a Time Limit.
IPv4 TTL decreases at routers; DNS TTL represents seconds of cache lifetime.
Study area: Protocols & logical ports · Batch 7
Relevant study for: CompTIA Network+ N10-009 · Cisco CCNA 200-301 · CompTIA A+ Core 1 220-1201 · CompTIA Security+ SY0-701 · ISC2 CISSP 2024 outline
Practice with exam flashcards →Networking & Connectivity / Knowledge library
TTL — Time to Live
Limits IPv4 packet forwarding and also names DNS cache lifetime fields.
Why learn TTL — Time to Live?
Limits IPv4 packet forwarding and also names DNS cache lifetime fields.
Where it came from
IPv4 TTL decreases at routers; DNS TTL represents seconds of cache lifetime.
- Memory aid (a learning cue, not the expansion): Traffic has a Travel Limit; cached records have a Time Limit.
Build your understanding
Work through these exercises in order. Try the task before opening a reference.
- Without looking, expand TTL: Time to Live.
- Recall this memory aid: Traffic has a Travel Limit; cached records have a Time Limit.
- Explain the practical use: Limits IPv4 packet forwarding and also names DNS cache lifetime fields.
- Explain this distinction: IPv4 TTL decreases at routers; DNS TTL represents seconds of cache lifetime.
- Identify TTL in a device specification, architecture diagram, or system inventory.
Documentation and sources
- IETF RFC 791 (www.rfc-editor.org)