Which part of an IP header are propossed by a router?

Routers primarily modify the "Time to Live" (TTL) field in the IP header as they forward packets. Each time a packet passes through a router, the TTL value is decremented by one to prevent packets from circulating indefinitely. Additionally, routers may also update the "Header Checksum" field to account for changes made to the header, ensuring data integrity. Other fields, like the source and destination IP addresses, remain unchanged during routing.