Homework 4: End-to-End Data Plane Forwarding

Given the network topology at the end of this document, answer the following questions.

1. Suppose an application on host A is sending a UDP packet to an application on host B. The application is bound to port 10000 on host A and port 20000 on host B. Fill in the source and destination addresses used at each layer of the protocol stack when the packet leaves Host A.

	Source	Destination
UDP Header: Port
IP Header: IP Address
Ethernet Header: MAC address

2. Suppose an application on host A is sending a UDP Packet to an application on Server 1. The application is bound to port 10000 on host A and port 30000 on Server 1. Fill in the source and destination addresses used at each layer of the protocol stack at every L3 hop along the way.

Hop 1	Hop 2	Hop 3
UDP Header Source Port : Dest Port:	UDP Header Source Port : Dest Port:	UDP Header Source Port : Dest Port:
IP Header Source IP: Dest IP:	IP Header Source IP: Dest IP:	IP Header Source IP: Dest IP:
Ethernet Header Source MAC Dst MAC	Ethernet Header Source MAC Dst MAC	Ethernet Header Source MAC Dst MAC

3. In hop 1, how does host A learn the addresses needed at each layer prior to sending the packet? The answer may be one or more of: manual or static host configuration, dynamically learned via some protocol (in which case state the protocol), dynamically selected by operating system, or well-known (i.e. some standard reserved value known a priori). Choose the most common mechanism for each address in above table.

4. Repeat the above question for hop 2. In this case, the addresses may also be known by virtue of the fact that they are carried in the packet.

5. Repeat the above question for hop 3.