{"id":78843,"date":"2026-09-25T13:48:55","date_gmt":"2026-09-25T13:48:55","guid":{"rendered":"http:\/\/bangla.sitestree.com\/?p=78843"},"modified":"2026-09-25T13:48:56","modified_gmt":"2026-09-25T13:48:56","slug":"do-routers-in-the-internet-core-use-mac-address","status":"publish","type":"post","link":"http:\/\/bangla.sitestree.com\/?p=78843","title":{"rendered":"Do routers in the Internet Core Use MAC address?"},"content":{"rendered":"\n

Yes \u2014 if the link between two routers is Ethernet<\/strong>, the packet is carried from one router to the next inside an Ethernet frame that uses MAC addresses<\/strong> for that particular hop.<\/p>\n\n\n\n

But the important distinction is:<\/p>\n\n\n\n

\n

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.<\/strong><\/p>\n<\/blockquote>\n\n\n\n

For example:<\/p>\n\n\n\n

Host A \u2192 Router 1 \u2192 Router 2 \u2192 Router 3 \u2192 Host B<\/code><\/pre>\n\n\n\n
Suppose all links are Ethernet.<\/p>\n\n\n\n
Hop 1: Host A \u2192 Router 1<\/h3>\n\n\n\n
IP packet:\nSource IP = Host A\nDestination IP = Host B\n\nEthernet frame:\nSource MAC = Host A MAC\nDestination MAC = Router 1 MAC<\/code><\/pre>\n\n\n\n
Hop 2: Router 1 \u2192 Router 2<\/h3>\n\n\n\n
Router 1 removes the old Ethernet frame, examines the IP packet, chooses Router 2 as the next hop, and creates a new frame<\/strong>:<\/p>\n\n\n\n
IP packet:\nSource IP = Host A\nDestination IP = Host B\n\nNew Ethernet frame:\nSource MAC = Router 1's outgoing-interface MAC\nDestination MAC = Router 2's MAC<\/code><\/pre>\n\n\n\n
Hop 3: Router 2 \u2192 Router 3<\/h3>\n\n\n\n
Again:<\/p>\n\n\n\n
Source MAC = Router 2\nDestination MAC = Router 3<\/code><\/pre>\n\n\n\n
The MAC addresses change at every Ethernet hop<\/strong>.<\/p>\n\n\n\n
So:<\/p>\n\n\n\n
IP addresses:  mostly end-to-end\nMAC addresses: hop-to-hop<\/code><\/pre>\n\n\n\n
A useful diagram is:<\/p>\n\n\n\n
Host A          R1             R2             R3          Host B\n IP A                                                   IP B\n\nMAC A \u2192 MAC R1\n                 MAC R1 \u2192 MAC R2\n                                  MAC R2 \u2192 MAC R3\n                                                  MAC R3 \u2192 MAC B\n\nIP A --------------------------------------------------> IP B<\/code><\/pre>\n\n\n\n
But not every Internet-core link has to use MAC addresses<\/h3>\n\n\n\n
This is the important qualification.<\/p>\n\n\n\n
A router-to-router link could use:<\/p>\n\n\n\n