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Note that the next hop’s IP address is in the router’s memory only: it does not appear in the packet at any time.This clears some points that always puzzled me:
If the gateway is identified by an IP address, but the destination host is also an IP address, which address exactly is put into the packet? And how can a packet be routed if the gateway's IP is itself part of the subnet that's supposed to be routed to it. (E.g. 192.168.0.0/24 with default gateway 192.168.0.1)
So the answer is, if I send the packet to host 1.1.1.1 but the routing table has 2.2.2.2 as the next hop, the packet will have 1.1.1.1 as the destination in the IP part but the MAC of 2.2.2.2 as destination of the Ethernet part (or equivalent). It doesn't matter which subnet the next hop's IP is in, as the routing table isn't consulted for it anyway - it's only used in ARP)
This leaves the question, why the indirection and why the mucking around with ARP and IPs that are never used as the destination to anything?
Couldn't you simply put the next hop's MAC address (instead of IP address) into the routing table and be able to route packets just as well, with a lot less complexity?
This clears some points that always puzzled me:
If the gateway is identified by an IP address, but the destination host is also an IP address, which address exactly is put into the packet? And how can a packet be routed if the gateway's IP is itself part of the subnet that's supposed to be routed to it. (E.g. 192.168.0.0/24 with default gateway 192.168.0.1)
So the answer is, if I send the packet to host 1.1.1.1 but the routing table has 2.2.2.2 as the next hop, the packet will have 1.1.1.1 as the destination in the IP part but the MAC of 2.2.2.2 as destination of the Ethernet part (or equivalent). It doesn't matter which subnet the next hop's IP is in, as the routing table isn't consulted for it anyway - it's only used in ARP)
This leaves the question, why the indirection and why the mucking around with ARP and IPs that are never used as the destination to anything?
Couldn't you simply put the next hop's MAC address (instead of IP address) into the routing table and be able to route packets just as well, with a lot less complexity?