determine ip and mac frame header information for a data packet

To be able to route packets, a router must know at a minimum the following.

To understand the complete process of how a packet moves from the source to the destination, consider the network shown in Figure 4-1.

When a response is received, it frames the packet with the source MAC address of Host1 and destination MAC address of Router1.

Since the packet is not destined to Router1, it must be routed out.

It finds that the destination network is reachable via Router2, so it frames the packet with the source MAC address of its exit interface (interface with the IP address of 10.1.1.1) and the destination address of Router2s interface.

This time the MAC address of Router2s exit interface is the source address while the MAC address of Router3 is the destination address.

At last the frame is sent out and reaches the destination host.

Hence the frame will need the MAC address of the default gateway as destination.

If Host3 does not have the MAC address of Router3, it will send an ARP query to get it.

Once Host3 has the MAC address, it will frame the segment and send it out to Router3.

From its routing table, it will know that the packet needs to go to Router2.

It will frame the packet with a source MAC address of its fa00 interface and the destination MAC address will be the address of Router2s fa01 interface and then send it out to the wire.

By the destination IP address it knows that the packet belongs to a directly connected interface.

The router uses that to create a frame with its fa00 interfaces MAC address as source and Host1s MAC address as destination and sends the frame out the interface.

You will see multiple questions about this on the CCNA exam The MAC address is only locally significant and changes each hop.

But as you have seen in the previous chapter, a new router has no configuration and the router is not going to discover remote networks by itself.

You will need to tell the router about the remote networks manually or configure it to learn the routes dynamically by talking to other routers.

I strongly suggest you setup the above network and configure the basic connectivity.

It will also allow you to practice everything learned in the previous chapter, once again.

Determine Ip And Mac Frame Header Information For A Data Packet