TTL: How does it work?

What is TTL?

Time-to-live, or for short just TTL, is a value that limits the amount of time or the number of hops that a data packet is set up for being alive. That could be on a network or in the cache memory. Once that time expires, either the number of hops reaches their limit, the data packets won’t be available anymore. 

There is a difference between the data packets. However, each of them holds its own TTL value. This time value is determined depending on the particular need of time or hops for the data packet to be alive. 

How does it work?

Let’s just picture the scenario in which the data packets do not have a TTL value at all. It is going to include the huge amounts of packets traveling all over the different routers constantly. For that reason, it is vital to set a limit and expiration for all of the data packets and successfully avoid this problem.

Thanks to the TTL value, we are able to track their route and understand for how long they have been alive.

For achieving their purpose and arriving at their successful target, data packets should travel through several network points. As we mentioned, each of them holds inside its own established TTL value. After receiving the data packet, routers should transfer it to the next network point. Yet, that is only possible if there are hops or time left available. In situations when there is no left amount of time or number of hops, the router is not able, and it is not going to proceed with transferring it. 

Instead, the router is going to send and inform with ICMP (Internet Control Message Protocol) message. That way, it notifies for IP errors and directs to the IP address source which issued the packet in the first place.

Quick Guide to Checking TTL Values

TTL, short for Time to Live, is essential in controlling how long data remains valid before an update is required. Here’s how to swiftly check TTL:

1. Using Command-Line Tools:

• Windows: Use ping [hostname] in Command Prompt to see the TTL value of a single packet.
• Unix/Linux/Mac: Use ping [hostname] to view the TTL for pings or dig +nocmd [hostname] +noall +answer for DNS records.

2. Online DNS Check Tools: There are online platforms that provide DNS lookup services where you can input a domain to retrieve its TTL values easily.

3. Browser Extensions: Some browser add-ons allow you to view the TTL for DNS records instantly as you browse the internet, streamlining the process.

Regularly checking the TTL will help you maintain an efficient network, ensuring information is neither outdated nor unnecessarily refreshed

What else is TTL used for?

Time-to-live is a vital value for controlling the period that data is going to be valid. Specifying its life lowers the portion of data going around and keeps the systems stress-free. With the help of TTL, everything is up to date. 

• Domain Name System (DNS). In the environment of DNS, TTL values serve to show the DNS resolving servers how long they should keep the DNS records in their cache memory. The DNS record types are a lot, and each of them holds its individual TTL value. Once the Time-to-live expires, the DNS resolving servers should obtain a fresh copy of the DNS records from the authoritative DNS server. Then, they are going to keep them as long as the new TTL is valid.
• Networking. In these circumstances, TTL prevents the infinite travel of the packets. With its help, we could track their route on the Internet.
• Content Delivery Network (CDN).  In this environment, TTL assists in knowing the duration the servers should keep the entire content they deliver, like photos and videos. After the TTL expires, servers drop the stored content. After that, they request the new information from the primary servers and cache them again. The exact procedure is going to repeat after the new TTL expires. These big networks have a presence all over the world. Thanks to the Time-to-live value, they keep duplicates of their content for enough period of time. That way, the primary servers are not saturated with consistent requests. The process is way more optimized and reduces bandwidth to serve faster distribution.