Which value, that is contained in an IPv4 header field, is decremented by each router that receives a packet?
The value that is decremented by each router that receives an IPv4 packet is called the Time To Live (TTL) field. The TTL field is a 1-byte (8-bit) field in the IPv4 header.
It is initially set by the source host and represents the maximum number of hops (routers) that the packet is allowed to pass through before it is discarded.
When a router receives an IPv4 packet, it decrements the TTL value by 1. If the TTL value reaches 0, the router discards the packet and sends an Internet Control Message Protocol (ICMP) Time Exceeded message back to the source host to inform it that the packet has expired.
The TTL mechanism is used for loop prevention and to ensure that packets do not circulate indefinitely in the network. By limiting the number of hops, the TTL field helps to prevent packets from being caught in routing loops or other unexpected network issues.
It’s important to note that although the term “Time To Live” implies a time limit, the TTL field represents the number of hops rather than an actual timer. The actual time taken to traverse a network hop can vary, so the TTL value is decremented regardless of the time it takes for each hop.
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