Yes — if the link between two routers is Ethernet, the packet is carried from one router to the next inside an Ethernet frame that uses MAC addresses for that particular hop.
But the important distinction is:
Routers decide where to send the packet using Layer 3 information such as the IP destination (or sometimes an MPLS label), not by using the final destination’s MAC address.
For example:
Host A → Router 1 → Router 2 → Router 3 → Host BSuppose all links are Ethernet.
Hop 1: Host A → Router 1
IP packet:
Source IP = Host A
Destination IP = Host B
Ethernet frame:
Source MAC = Host A MAC
Destination MAC = Router 1 MACHop 2: Router 1 → Router 2
Router 1 removes the old Ethernet frame, examines the IP packet, chooses Router 2 as the next hop, and creates a new frame:
IP packet:
Source IP = Host A
Destination IP = Host B
New Ethernet frame:
Source MAC = Router 1's outgoing-interface MAC
Destination MAC = Router 2's MACHop 3: Router 2 → Router 3
Again:
Source MAC = Router 2
Destination MAC = Router 3The MAC addresses change at every Ethernet hop.
So:
IP addresses: mostly end-to-end
MAC addresses: hop-to-hopA useful diagram is:
Host A R1 R2 R3 Host B
IP A IP B
MAC A → MAC R1
MAC R1 → MAC R2
MAC R2 → MAC R3
MAC R3 → MAC B
IP A --------------------------------------------------> IP BBut not every Internet-core link has to use MAC addresses
This is the important qualification.
A router-to-router link could use:
- Ethernet → MAC addresses are used
- PPP → no Ethernet MAC addressing
- MPLS → labels may be used for forwarding through the provider network
- other Layer-2 technologies → their own framing/addressing rules
Today, Ethernet is very common even between routers, so MAC addresses are often involved. But it is more accurate to say:
Each router forwards the IP packet to the next hop using the Layer-2 mechanism of that particular link. If the link is Ethernet, that mechanism includes source and destination MAC addresses.
So I would not say:
“The Internet core routes packets using MAC addresses.”
I would say:
The Internet core routes packets using Layer 3 routing, while each individual Ethernet hop uses MAC addresses to deliver the frame to the next router.
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