A layered protocol stack is designed to simplify network communication by separating functionalities into distinct layers. Each layer has a defined role and communicates with the layers directly above and below it. The main benefits of this model include:
Simplified design and implementation: Developers can focus on one layer without needing to understand the entire system.
Flexibility: New protocols can be developed and inserted at specific layers without redesigning the whole stack.
Interoperability: Standard interfaces allow different systems and vendors to work together.
Isolation of functions: Errors and updates can be managed within one layer without impacting others.
However,reducing protocol overhead is not a primary goalof this model. In fact, the encapsulation and interaction between layers can sometimesintroduce extra overhead. This overhead is a trade-off accepted to gain the other benefits listed above.
[Reference:Nokia IP Networking Fundamentals Study Guide – Chapter 2: "Layered Protocol Architectures", Section: "Benefits and Goals of Layered Models", , ]
Question # 5
In MAC address 00-20-60-CE-2B-28, which part is the Organisationally Unique Identifier (OUI)?
AMAC address(Media Access Control address) is a 48-bit identifier typically expressed in six groups of two hexadecimal digits (e.g., 00-20-60-CE-2B-28). It consists of two key parts:
OUI (Organizationally Unique Identifier)– The first24 bits(or first 3 octets, e.g., 00-20-60) are assigned by theIEEE to hardware manufacturers. This identifies the vendor or manufacturer.
Device Identifier (NIC Specific)– The remaining24 bits(e.g., CE-2B-28) are assigned uniquely by the vendor to each device/interface.
So in the address 00-20-60-CE-2B-28:
00-20-60 is theOUI
CE-2B-28 is thedevice-specific portion
Thus, the correct answer isD. 00-20-60.
[Reference:, IEEE MAC Address Standard (IEEE 802), Nokia IP Networking Fundamentals Study Guide – Chapter: "Ethernet Addressing", , , ]
Question # 6
In which of the following types of network would STP be used?
A.
An MPLS network with multiple LSPs to the same LER.
Spanning Tree Protocol (STP)is used specifically inEthernet Layer 2 networkstoprevent loopscaused byredundant paths.
STPdetects loops and blocks one or more redundant pathsto ensure there is aloop-free topologyin a bridged network.
STP dynamicallyrecalculates the topologyif a link fails, reactivating previously blocked paths.
Explanation of other options:
A. MPLS with LSPs:MPLS uses its own mechanisms for path management, such as RSVP or Segment Routing. STP is not applicable here.
C. OSPF with ECMP (Equal-Cost Multi-Path):OSPF is a Layer 3 protocol that inherently supports multiple paths without loops; STP is not involved.
D. eBGP (Exterior Border Gateway Protocol):Operates at Layer 3 for inter-AS communication; STP is not used in BGP routing.
Therefore,Option Bis correct, as STP is explicitly designed forLayer 2 Ethernet networkswithredundant paths.
[Reference:, Nokia IP Networking Fundamentals Study Guide – Chapter: "Layer 2 Technologies", IEEE 802.1D Standard – Spanning Tree Protocol Overview, , , ]
Question # 7
How many subnets and host addresses are obtained by subnetting network 201.148.26.0/24 using a /26 subnet mask?
BGP (Border Gateway Protocol)uses amulti-step decision processto select the best route among multiple paths. It doesnot use SPF or simple metrics like hop count.
Key BGP selection criteria include:
Local preference
AS path length
Origin type
MED (Multi-Exit Discriminator)
eBGP over iBGP
IGP metric to next hop
Option C is correct– BGP evaluatesmultiple attributesfor route selection.
[Reference:, Nokia IP Routing Fundamentals – BGP Route Selection, RFC 4271 – BGP Decision Process, ===========]