after looking up its routing table, does a router add next hop's address into this packet?

Question

i didn't mean changing the source or destination, but adding another address, the address of next hop.

Answer 1

No. It's like the post office system. The packet has the destination and sender's address. The routers are the various sorting mechanisms of the post office depots. Through Routing Information Protocol (RIP) they know where to pass a packet on to get it to its destination.

Answer 2

if it doesn't do that, how is the next router supposed to receive the packet? of course it does.