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Cache-Control: max-age measured in seconds. Expires field refers a time after which the response is considered stale.

I used “curl” as a client to create a GET request for The server responded with “ Expires” and “Cache-Control: max-age” fields, notifying me how long I should keep the resource in the cache. The following figure summarizes the flow. I have a http request and response from one of our previous articles. HTTP uses “ Expires” and “Cache-Control: max-age” header fields to control caching. TTL in HTTP lets the client know how long a resource (an image, a html, a media, etc.) should be stored locally before the client (browser) makes a new request for a copy of the resource. TTL in Hyper Text Transfer Protocol (HTTP) Each record includes a TTL with value of 4 which means that the client should cache the record for 4 seconds. In the figure below, the client is querying the DNS server, asking about The DNS server (8.8.8.8) sends a DNS response to the client (192.168.1.52) with multiple “A” record inside the packet.

It is set by DNS server, informing the client (resolver) how long it should keep the DNS record in its cache before requesting a new one. When it reduces to 0 (zero), the packet gets dropped and an ICMP packet is sent back to the sender.ĪLSO READ: Defensive Programming Techniques Explained with Examples The TTL value is decreased by 1 every time the packet passes through a layer 3 device. TTL is 1-byte field which can be set to maximum 255. The purpose of TTL in IP headers is to prevent a network packet from circulating indefinitely. It refers to the number of hops that a packet can travel through before it gets discarded by a layer 3 device. Since it is a broad definition, I will break it into 3 categories to explain it better. The generic definition of Time to Live (TTL) refers either life time of a network packet or expiration time of the cached data in a computer.