When a packet is forwarded through a network from one host to another host, which of the following fields in
the Ethernet frame will change at every hop?
A.
Source IP address
B.
Destination MAC address
C.
Source port number
D.
Destination IP address
Explanation:
When an Ethernet frame is forwarded through the network, both the source and destination MAC addresses will
change at every hop.
The source and destination IP addresses and source and destination port numbers MUST remain the same for
proper routing to occur, for the proper delivery to the destination service, and for the proper reception of
responses to the sending device. By contrast, the MAC addresses used at each hop must be those of the
physical interfaces involved in the Layer 2 forwarding at each hop.
As a simple illustration of this process, IP addresses and MAC addresses are assigned to two computers and
three routers shown in the diagram. The network is arranged as shown below:
The IP addresses and the MAC addresses of each device are shown below:
There will be four handoffs to get this packet from WKS1 to WKS2. The following table shows the destination IP
addresses and destination MAC addresses used at each handoff.
As you can see, the destination IP address in the packet does not change, but the MAC address in the frame
changes at each handoff.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Interpret Ethernet frame formatReferences:
MAC address changes for every new network
