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How is network layer addressing accomplished in the OSI protocol suite?A. Internet Protocol addressB. Media Access Control addressC. Packet Layer Protocol addressD. Network Service Access Point addressE. Authority and Format Identifier address
Ans: D
Network Layer Addressing
OSI network layer addressing is implemented by using two types of hierarchical addresses:
network service access point addresses and network entity titles.
A network service access point (NSAP) is a conceptual point on the boundary between the
network and the transport layers. The NSAP is the location at which OSI network services
are provided to the transport layer. Each transport layer entity is assigned a single NSAP,
which is individually addressed in an OSI internetwork using NSAP addresses.
Subsection: NSAP ADDRESSING (6 questions)
Q 1
How are network layer addresses accomplished in the OSI model?A. Internet Protocol addressB. Media Access Control addressC. Packet Layer Protocol addressD. Network Service Access Point addressE. Authority and Format Identifier address
Ans: D
Explanation: The term "network address" is used to refer to the Network Service Access Point
(NSAP) at which the OSI Network Service is made available to a Network Service user by the
Network Service provider.
Reference: RFC 941, Addendum to the Network Service Definition Covering Network Layer
Addressing
Incorrect Anss
A: IP is a protocol that is based on the OSI model.
B: MAC addresses operate at a lower level in the OSI model.
C, E: Do not apply.
Q2
Decipher the area ID from the following OSI IS-IS NSAP address:
47.040C.0061.040C.0056.0D12.00A. 00B. 46C. 47.040CD. 47.040C.0061E. 040C.0056.0D12
Ans: D
Explanation:
An NSAP address (figure 7) has two major parts: the initial domain part (IDP) and the domain
specific part (DSP) (Figure 7). The IDP consists of a 1-byte authority and format identifier (AFI)
and a variable-length initial domain identifier (IDI), and the DSP is a string of digits identifying
particular transport implementation of a specified AFI authority. Everything to the left of the
system ID can be thought of as the area address of a network node.
Figure 7 The NSAP address
Reference:
http://www.cisco.com/en/US/tech/ CK3 65/ CK3 81/technologies_white_paper09186a00800a3e6f.shtm
Q3
Decipher the area ID from the following OSI IS-IS NSAP address:
47.040C.0061.040C.0056.0D12.00A. 00B. 47C. 47.040CD. 47.040C.0061E. 040C.0056.0D12
Ans: D
Explanation:
SEL is the rightmost octet:
47.040C.0061.040C.0056.0D12.00
SystemID is next six octet:
47.040C.0061.040C.0056.0D12.00
The AreaID is the remaining leftmost octets:
47.040C.0061.040C.0056.0D12.00
Note: There are several NSAP formats. This is an OSI NSAP format (the second in the sample
below).
Sample:
Reference: Introduction to Intermediate System-to-Intermediate System Protocol,
http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/insys_wp.htm
Incorrect Anss
A: 00 is the SEL.
B, C: 47 and 47.040C is just a part of the Domain
E: 040C.0056.0D12 is the SystemID.
Q4
Which of the Ans choices below represents a valid: private, locally administered NSAP
address?A. 39.0f01.0002.0000.0c00.1111.00B. 48.0f01.0002.0000.0c00.1111.00C. 49.0004.30ac.0000.3090.c7df.00D. 52.0f01.0002.0000.0c00.1111.00
Ans: A
Explanation: The private NSAP addresses have AFI beginning with 39, 45 and 47.
AESA Network Service Access Point (NSAP) ATM Addresses
There are 3 types of private ATM addresses:
o NSAP encoding format for E.164 addresses - The authority and format identifier (AFI)
is 45. These addresses are used in establishing ISDN calls by public networks, and they a
normally used in public telephony.
o Data Country Code (DCC) AESA - The AFI is 39. These addresses are to be used in
public networks. For example, the initial domain identifier (IDI) value 0x84.0f identifies
the United States.
o International Code Designator (ICD) AESA - The AFI is 47. These addresses are used
in private organizations, and the ICD field indicates the code set or organization. Cisco
uses by default ICD addresses.
Reference:
http://www.cisco.com/en/US/tech/ CK3 9/ CK4 9/technologies_tech_note09186a00800c9761.shtml
Q5
You are a guest lecturer at the CertKing Academy and are preparing a lesson on the Cisco
NSAP address System IDs? (Select three)A. System IDs can vary in size within a domain.B. The System ID identifies a node in an IS-IS network.C. The System ID must be unique within a Level-1 area.D. The System ID must be unique within a Level-2 area.E. The System ID must be the MAC address of the router.
Ans: B, C, D
Explanation:
B: Each system ID within an area must be unique. It is used to identify a IS-IS node.
C: All Level 1 routers and hosts in an area must have an NSAP with the same area address.
D: Level 2 routers advertise their own area addresses (NSAP) to the other Level 2 routers in the
backbone.
Reference: Introduction to Intermediate System-to-Intermediate System Protocol
http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/insys_wp.htm
Incorrect Anss
A: All ISs and ESs in a routing domain must have system IDs of the same length. Furthermore,
Cisco implements a fixed length of 6 bytes for the system ID.
E: There are several techniques for creating unique system IDs
* Start numbering 1, 2, 3, 4, and so on.
* Use Media Access Control (MAC) addresses.
* Convert and use the loopback IP address: 192.168.11.1 --> 192.168.011.001-->
1921.6801.1001.
Q6
You are the network engineer at CertKing . Your newly appointed CertKing trainee wants t
know what the difference between an OSI NSAP address and a Network Entity Title
(NET)is.
What will your reply be?A. A NET is an NSAP address with the N-selector byte set to 00.B. Network Entity Titles do not have to start and stop on byte boundaries.C. The System ID field of the NSAP address does not uniquely identify a node.D. To identify a Domain, and NSAP address must be used because a NET can only identify
an Area.E. A NET is a special version of an NSAP address restricted to 8 bytes for the Area Address
System ID and the N-Selector byte.
Ans: A
Explanation:
NETs and NSAP
NETs and NSAPs are ISO addresses. The differences between the NET and NSAP addresses are subtle. The N
address is the address of the host, where the value in the NSEL field is set to 0x00. Therefore, there is no upper-lay
protocol identified within the host. With no application identified within the end host, the packet can be routed
to
destination, but it cannot be handed off to a process after it has been delivered. However, routers do not have
upp
layer protocols to identify because they are transitory ISs. Therefore, the NSAP of the router is referred to as a
N
because the NSEL field is set to 00. The NSAP is the full ISO address. It not only defines the area and
destination h
within the area, but also specifies where to send the incoming packet after it has reached the host. The NSEL
field
the end of the ISO address specifies the upper-layer protocol and is similar to the Protocol field of the IP header.
Network Entity Title (NET) In IS-IS, this is the ISO address of the system, but not to the process destination
with
the system. The NET describes both the area and system ID of a system in the IS-IS network but excludes the
NSE
which is set to 0x00. If the NSEL identifies the process within the system, the ISO address is called the "NSA
address."
Network Service Access point (NSAP) In IS-IS, this describes a service at the network layer to which the packe
to be directed. The NSAP is the NET address with the NSEL field set to a positive value, a value other than
0x00.
Network entity title (NET)
The NET describes both the area and system ID of a system in the IS-IS network but excludes the NSEL, which
defines the NSAP address of the system.
Network service access point (NSAP)
Describes a service at the network layer to which the packet is to be directed. The NSAP is the NET address
with th
SEL field set to a value other than 0x00.
Section 11: Identify similarities and differences between Integrated ISIS
and OSPF (4 questions)
Q
Drag the routing protocol characteristics on the left to the corresponding OSPF box in the
middle or the corresponding IS-IS box on the right.
Q2
There routing protocols OSPF and IS-IS share many characteristics. Which four of the
characteristics below do they share? (Select four)A. link-state databaseB. backbone area designC. Shortest Path First (SPF) algorithmD. Update, Decision, and Flooding ProcessE. Hello protocol to establish and maintain adjacencies
Ans: A, C, D, E
Explanation:
A: IS-IS use a link-state database.
C: The IS-IS decision process runs shortest-path-first (SPF) algorithm on the link-state database,
and creates the forwarding database.
D: The Update, Decision, and Flooding Process of IS-IS and OSPF are similar.
E: Routers running IS-IS will send hello packets out all IS-IS-enabled interfaces to discover
neighbors and establish adjacencies. This is similar to OSPF.
Reference: Introduction to Intermediate System-to-Intermediate System Protocol
http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/insys_wp.htm
Incorrect Anss
B: IS-IS does not have a backbone area like the OSPF area 0. The IS-IS backbone is a
contiguous collection of Level 2-capable routers, each of which can be in a different area.
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