GATE2004-IT-27

Question

A host is connected to a Department network which is part of a University network. The University network, in turn, is part of the Internet. The largest network in which the Ethernet address of the host is unique is

• A. the subnet to which the host belongs
• B. the Department network
• C. the University network
• D. the Internet

Comments

@Bikram sir

i have a doubt that  question is asking about largest network we choose option d  thts fine

but in general for all department,subnet of host,university  ,MAC address will be unique for specific host .

how spoofing will work?

Answer 1

Answer is D, Ethernet address is nothing but MAC Address which is present on NIC and it is unique for every network device (a single system might have multiple network cards and each can have its own MAC address).

PS: We can never say Ethernet address is unique only in a network -- because it is independent of the network a device is connected to. That is, if we move a device from one network to another, MAC address remains same. Of course we can do spoofing, but this is not relevant to the asked question.

Comments

Ethernet address is same as Mac address .

MAC addresses are most often assigned by the manufacturer of a network interface controller (NIC) and are stored in its hardware. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as  to as the burned-in address (BIA) . It may also be known as an Ethernet hardware address (EHA), hardware address or physical address  ...[1] [2]

https://en.wikipedia.org/wiki/MAC_address

https://www.net.princeton.edu/enetAddress.howto.html

As the largest network  is Internet itself where this MAC address is Unique .

Hence D is the correct answer .

---

sir but why do we say that mac addresses are not unique as the different manufacturers follow different so two devices from two different manufacturers can have same mac address

---

if these mac addresses are unique over thw internet then why do we need an alternate ip address i still didn't

get uu r point can u plzz elaborate

---

@vishal

mac addresses is provided by a manufacturer so it is different for different manufacturer .

you can read this for the difference https://www.cs.duke.edu/csl/docs/sysadmin_course/sysadm-339.html

---

@vishal goyal 

IP Addresses are allocated by an network administrator  to each communicating device in a network.  A MAC Address is a unique device specific address for each devices in all networks . Each device have only one MAC address but different network have different IP address.

The main difference is IP address can change with the change in network but your device MAC address is unchanged in different networks.

And there is ARP protocol convert IP address into MAC address.

---

https://gateoverflow.in/105481/which-device-have-exactly-address-work-station-router-gateway 

answer this once  plzzzzzzzzzz

---

The MAC address contains details like Vendor id, date of manufacture and serial no. So for two different manufacturers, their vendor id will be different. Hence no 2 MAC addresses are same.

---

what to say about this screenshot taken from Forozuan's book:

---

In general by ethernet address we mean Mac address or physical address. And physical address should be unique in the network it is a part of.
So why are we taking it as globally unique??

---

what will be the answer if instead of mac addess ip address is asked?

---

A vendor can always duplicate MAC address on exhaustion of allocated range. Isn't this question ambiguous?

---

They are talking about physical address over there and not the MAC address. MAC address is used as a physical address and it is universally unique. But MAC address doesn't have to be universally unique to be used as physical address. When talking about "physical address" they are talking conceptually. For an address to be locally unique is a sufficient condition for it to be a physical address.

---

In all the options given, the device will have a unique host as the admin of router maintains a mapping table.. which maintains the device's assigned IP with the device's MAC address.

(In IPV4, each computer sends a request packet to the router before establishing connection and hence the router maintains a mapping table of assigned IPs)

Now, the biggest network is Internet.

(The other answers given here say that D is correct due to unique MAC addresses in ethernet.. every network has a unique MAC address anyway, but biggest is the Internet.)

---

@Bikram sir the comment by manu thakur says that physical address is unique locally but not universally like internet and also example of physical address is Mac address so how Mac address can be unique globally 

Answer 2

The answer should be (D) since a specific LAN technology - Ethernet is mentioned here, so MAC addresses will be specifically taken as physical address which is unique in the entire world.!

If in general LAN Address was mentioned, then we would have had to take Physical Address concept, which only needs to be unique within the network, so answer would have been A in that case.

Answer 3

Answer is D.

Because the Ethernet address will be unique for every host.

Answer 4

Answer should be D.

As a media access control address (MAC address) of a device is a unique identifier assigned to a network interface controller (NIC) for communications at the data link layer of a network segment.

Source: https://en.m.wikipedia.org/wiki/MAC_address

Answer 5

ans a)

Answer 6

ans should be (A)

Comments

Answer must be D according to IPv6 protocol because in IPv6 MAC address itself the part of Ip address so..it's unique throughout INTERNET.