Based on my understanding, when a packet reaches a router, the Data Link layer header (and trailer if there is a trailer) will be removed from the packet and a new header (and a new trailer if there is a trailer) will be added to the packet.
But is the header of any other layer (other than the Data Link layer) is also removed and re-added when reaching a router?
Of course I am talking about the layers in the OSI model.
But is the header of any other layer (other than the Data Link layer) is also removed and re-added when reaching a router?
No. Routing happens at layer-3, so any information below layer-3 is removed, and anything at or above layer-3 is preserved. Because the TTL is decremented, the IPv4 checksum must be recalculated in the IPv4 header, but IPv6 does not have a header checksum, so decrementing the Hop Count does not need to recalculate a checksum.
If NAT or NAPT is also performed on a router, the layer-3 header is modified (address and checksum), and the header of TCP, UDP, or ICMP must also be modified (possibly port or ICMP query number and checksum), but that is not inherent in routing.
