Which value in an IPv4 header is decremented with each router that receives the packet?

In an IPv4 packet header, the value that is decremented with each router that processes the packet is the Time-to-Live (TTL) field. The TTL field is designed to prevent packets from circulating indefinitely in the network in case of routing loops.

When a packet is sent, it starts with an initial TTL value that is typically set by the originating device. Each time the packet is forwarded by a router, that router decreases the TTL value by one. If the TTL reaches zero before the packet arrives at its destination, the packet is discarded, and an Internet Control Message Protocol (ICMP) message may be sent back to the sender to indicate that the packet could not be delivered.

This mechanism helps in maintaining the health of the network and ensures that resources are not wasted on packets that would otherwise travel endlessly through the network without reaching their destination.