---------------------------------------------------------------------------
Mohamed G. Gouda						CS 356
Spring 2019							Midterm 3
---------------------------------------------------------------------------

(1)
Consider a Switched Ethernet SE that has 15 hosts, 2 switches, and 1
interface to a router R whose other interface connects R with the rest of
the Internet. How many IP addresses are used in this SE ? Explain your
answer.
--------------------------------------------------------------------------- 

(2)
Let S be a switch in a Switched Ethernet SE. Assume that the switching
table of S has an entry 
	e = (dst=M25, interface=15, TTL)

(a) Describe how e is updated when S receives a frame
	(src=M25, dst=M12)
via interface 17.

(b) Describe how e is updated when S receives a frame
	(src=M12, dst=M25)
via interface 15.
---------------------------------------------------------------------------

(3)
Consider a Switched Ethernet SE that has 20 hosts, 3 switches, and 1
interface to a router R whose other interface connects R with the rest of
the Internet. what is the maximum number of entries that can co-exist in
the switching table of any switch in SE.
---------------------------------------------------------------------------

(4)
Attached to a Switched Ethernet SE is a host whose IP address is H and
whose MAC address is M. Host H can send a packet P over SE to another
host whose IP address is H' according to the following protocol:

	1. H encapsulates P in a frame F and broadcasts F to every
	host attached to SE.

	2. Every host attached to SE receives F and checks whether
	this host is the one intended to receive P and decides
	whether to keep or discard P.

The header of F has the following three fields:

	src MAC address = ?
	dst MAC address = ?
	Data            = ?

What are the values that H assigns to these three fields ?
----------------------------------------------------------------------------
Solutions:
----------------------------------------------------------------------------

(1)
This SE has 1 IP address for each interface of a host. Also this SE has 1
IP address for the router interface that is in SE. Thus this SE has a 
total of 16 IP addresses.

----------------------------------------------------------------------------

(2)(a)
Entry e is changed to become (dst=M25, interface=17, TTL=max-value).
(2)(b)
Entry e remains unchanged.
----------------------------------------------------------------------------

(3)
The maximum number of entries that can co-exist in the switching table of any
switch is 21. (For an explanation, see solution (1) above.)
-----------------------------------------------------------------------------

(4)
	src MAC address = M
	dst MAC address = FFFFFFFFFFFF
	Data            = Packet P
-----------------------------------------------------------------------------
---------------------------------------------------------------------------
Mohamed G. Gouda						CS 356
Spring 2019							Midterm 3A
---------------------------------------------------------------------------
(1)
Consider a Switched Ethernet SE that has 15 hosts, 2 switches, and 1
interface to a router R whose other interface connects R with the rest of
the Internet. How many MAC addresses are used in this SE ? Explain your
answer.
--------------------------------------------------------------------------- 

(2)
Let S be a switch in a Switched Ethernet SE. Assume that the switching
table of S has an entry 
	e = (dst=M25, interface=15, TTL)

(a) Describe how e is updated when S receives a frame
	(src=M25, dst=M11)
via interface 15.

(b) Describe how e is updated when S receives a frame
	(src=M12, dst=M25)
via interface 15.
---------------------------------------------------------------------------

(3)
Consider a Switched Ethernet SE that has 17 hosts, 3 switches, and 1
interface to a router R whose other interface connects R with the rest of
the Internet. What is the maximum number of entries that can co-exist in
the switching table of any switch in SE.
---------------------------------------------------------------------------

(4)
Attached to a Switched Ethernet SE is a host whose IP address is H and
whose MAC address is M. Host H can send a packet P over SE to another
host whose IP address is H' according to the following protocol:

	1. H encapsulates P in a frame F and broadcasts F to every
	host attached to SE.

	2. Every host attached to SE receives F and checks whether
	this host is the one intended to receive P and decides
	whether to keep or discard P.

The header of F has the following three fields:

	src MAC address = ?
	dst MAC address = ?
	Data            = ?

What are the values that H assigns to these three fields ?
---------------------------------------------------------------------------
Solutions:
---------------------------------------------------------------------------

(1)
This SE has 1 MAC address for each interface of a host. Also this SE has 1
MAC address for the router interface that is in SE. Thus this SE has a 
total of 16 MAC addresses.

----------------------------------------------------------------------------

(2)(a)
Entry e remains unchanged except that its TTL is assigned its max value.
(2)(b)
Entry e remains unchanged.
----------------------------------------------------------------------------

(3)
The maximum number of entries that can co-exist in the switching table of any
switch is 18. (For an explanation, see solution (1) above.)
-----------------------------------------------------------------------------

(4)
	src MAC address = M
	dst MAC address = FFFFFFFFFFFF
	Data            = packet P
---------------------------------------------------------------------------