Network Automator

Did you know that a router Can Foward Ethernet Frames just like a switch?

Did you know that a router Can Foward Ethernet Frames just like a switch?

If packet arrives at router- with the destination address of the encapsulated Ethernet destination field same as the router’s address. It either means the Ethernet frame arrived here because….

A) The packets destination IP is configured on the router and it has arrived at its final destination.

Or

B) If the destination IP field is not configured on the router interface then we must “route”

1. Now the routing table in the control plane provides the logic(longest match) to route the packet recursively, then the data plane’s FIB(forwarding information base) table will forward the packet to the correct egress interface of the packets destination route.
2. In order to forward the packet to the correct interface the router needs the layer 2 details of the interface that’s located in the FIB, this is where the Adjacency table(CAM/TCAM) comes in.

3. The router will now locate the source MAC and the destination MAC through the adjacency tables. The router will then discard the old frame and recreate the a new frame with correct source/destination mac. Inherently it is the the adjacency table that provides the necessary fields to rewrite the frame header.
4. Once the frame header is rewritten with correct destination MAC and and Source, it will forward but before it performs the forwarding(like a switch), it will recalculate the IP packet TTL. It will decrease TTL by 1 and subsequently because of this amendment to packet the IP header checksum will need to be recalculated too.

the data plane’s FIB(forwarding information base) table will forward the packet to the correct egress interface to the packets destination route.