(a) Assume a host A wants to send an IP message to another host B. Assume A know
ID: 658552 • Letter: #
Question
(a) Assume a host A wants to send an IP message to another host B. Assume A knows its
own configuration information (of course) and it knows the IP address of B. How does A
determine if it should forward the message to its default router or if it should forward the
message directly to B?
(b) Assume a small company has a single Ethernet with a subnet number 198.16.28.0/24.
This is the only address block of the company. Assume a router R is connected to this
Ethernet, and assume that a host H in the company does not support Ethernet (very old
host!), so a modem connection is established between the router R and the host H. How
would this affect the set of addresses given to the Ethernet?
Explanation / Answer
Answer:
a)
When host A knows his IP address configuration then he will know the network address too. Similarly, when host A knows the IP address of the host B then he will know the network address of the host B too.
Now in-order to forward a message to host B directly or indirectly is decided by the network addresses of both the hosts. The decision is based on either of the below conditions.
If they have same network addresses then host A can send the message directly to host B.
If they does not have same network addresses then host A need to forward the message to its default router.
b)
Explanation of the effect of the set of addresses given to the Ethernet when a single host is connected to the Router directly apart from its Ethernet connection:
According to the problem description, the company has only one single Ethernet. This explains clearly that the systems are working with one network address.
The subnet number given is 198.16.28.0/24.
This address specifies that 24 bits are assigned for the network address. The remaining 8-bits are used to assign the host IP addresses.
So, by using 8 bits one can assign 28=256 hosts to the same network.
Now, it is specified that one of the host that is host H is not supportable by the given Ethernet.
Even specified that host H is directly connected to the router by using modem.
One point need to be understood that when a router is getting connect to two different networks, and then it has to update its routing table too.
Since, only a single system is connected separately to the router apart from the given Ethernet connection.
So, among 8 bits, 1 bit is being assigned as separate network. But the company has only one Ethernet connection. This clearly specifies that 7 bits are used to assign the hosts of the Ethernet.
That means only 127 systems can be connected to the Ethernet. Thus, it is clear that the number of hosts that can be connected to the single Ethernet will reduced to half. The other half of the IP addresses cannot be used to connect the systems under this Ethernet.
Thus, it affects the set of addresses given to the Ethernet.
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