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One of the features that OSPF and IS-IS both share is their use of a backbone area. In
OSPF the backbone is classified as Area 0. How is an IS-IS backbone area numbered?A. Area 0B. Area 1C. Any legal area number.D. There is no backbone area number.
Ans: D
Explanation: 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
Reference: Cisco, Introduction to Intermediate, System-to-Intermediate System Protocol
http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/insys_wp.htm
Q4
Which three characteristics apply to IS-IS but not to OSPF? (Choose three)A. Encapsulates PDUs directly into a data-link frame.B. Uses a DIS and a backup DIS to present the pseudo-node on the LAN.C. Uses stubby areas to improve network scalability.D. Uses a default IOS metric of 10 on each interface.E. Runs PRC (Partial Calculations) to calculate IP reachability information.F. Uses an on-demand circuit to reduce the hello and LSA flooding across switched WAN
links, such as ISDN.
Ans: A, D, E
Ans "D" -- Page 617 of CCIE Professional Development Routing TCP/IP Volume I by Jeff Doyle
* Ans "E" -- "PRC is the software's process of calculating routes without performing an SPF
calculation."
Configuring Integrated IS-IS (pdf document) - IPC-271, page 11 of 16
* Ans "A" -- ??
- There is no such thing as a Backup DIS in IS-IS so "B" is not correct
- D and E are already taken
- The remaining possible Anss are: A, C, or F
- We think the most correct Ans is "A", Encapsulates PDUs directly into a data-link frame.
Section 12: List the types of IS-IS routers and their role in IS-IS area
design (6 questions)
Q
There are several varieties of IS-IS routers. Two types of IS-IS provide intra-area routing
services. Which of the following two match this description? (Select two)A. L1 ISB. L1 ESC. L2 ISD. L2 ESE. L1/L2 IS
Ans: A, E
Explanation: L1 IS and L1/L2 IS routers provide intra-area routing services.
Reference: RFC2966
Q2
How could you describe the backbone area of an IS-IS domain?A. A contiguous collection of L1 routers.B. A contiguous collection of L1 and L1/L2 routers.C. A contiguous collection of L1 and L2 routers.D. A contiguous collection of L2 and L1/L2 routers.
Ans: D
Explanation: In IS-IS, the backbone is a collection of L2 and L1/L2 routers.
Q3
Which one of the following statements correctly describes a characteristic of an IS-IS
backbone?A. A router in all areas.B. All routers in one area.C. A chain of L2 and L1/L2 IS-IS routers.D. An unbroken string of L1 and LS IS-IS routers.E. A central area to which all other areas are attached.
Ans: C
Explanation: L1 routers are internal to the area and so only L2 and L1/L2 routers form the
backbone in IS-IS.
Q4
The routing protocol IS-IS uses areas. What must an administrator connect each IS-IS area
to?A. Area 0B. Area 1C. Level-1 backboneD. Level-2 backboneE. External IS-IS areas
Ans: D
Explanation: Small IS-IS networks are built as a single area that includes all the routers in the
network. As the network grows larger, it is usually reorganized into a backbone area made up of
the connected set of all Level 2 routers from all areas, which is in turn connected to local areas.
Reference: Cisco, IS-IS Multiarea Support
Incorrect Anss
A, B: Area 0 or Area 1 has no special significance in IS-IS.
C: Level 2, not Level 1.
E: This is not a requirement.
Q5
Which one of the following features are a distinguishing trait of an IS-IS backbone?A. a router in all areasB. all routers in one areaC. a chain of L2 and L1/L2 IS-IS routersD. an unbroken string of L1 and L2 IS-IS routersE. a central area to which all other areas are attached.
Ans: C
Explanation: IS-IS backbone is a contiguous collection of Level 2-capable routers, each of
which can be in a different area
Reference: Introduction to Intermediate System-to-Intermediate System Protocol,
http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/insys_wp.htm
Q6
The newly appointed CertKing trainee wants to know what area number is assigned to an
IS-IS backbone.
What will your reply be?A. 0B. 1C. Any legal are number.D. There is no backbone area number.
Ans: D
Explanation:
OSPF requires that an area be defined as a backbone area and that each other area border that
backbone area. Special configuration (a virtual link) is required for any area that does not border
the backbone area. IS-IS backbone routers can reside in any area. There merely must be an
unbroken chain of Level 2 or Level 1/2 routers in order for the backbone to function.
The IS-IS backbone is a contiguous collection of Level-2 capable routers, each of which can be
in a different area.
Subsection: GENERAL IS-IS (12 questions)
Q 1
Which of the following three statements correctly describe the characteristics of IS-IS? (select
three)A. L1 routers have no knowledge about routes outside their area.B. L1/L2 routers maintain a separate Level 1 link-state database and a Level 2 link-state database,
they do not advertise L2 routes to L1 routers.C. To route packets to another area, L1 routers must forward the packets to the L2 router of the
destination area.D. To route packets to another area, L1 routers must forward the packets to an L1/L2 router within
their area.E. L2 routers form adjacencies with L1 and L1/L2 neighbors.
Ans: A, B, D
Explanation:
Intermediate System-to-Intermediate System (IS-IS) is an OSI link-state hierarchical routing protocol
that floods the network with link-state information to build a complete, consistent picture of network
topology. To simplify router design and operation, IS-IS distinguishes between Level 1 and Level 2 ISs.
Level 1 ISs communicate with other Level 1 ISs in the same area. Level 2 ISs route between Level 1
areas and form an intradomain routing backbone. Hierarchical routing simplifies backbone design
because Level 1 ISs need to know only how to get to the nearest Level 2 IS. The backbone routing
protocol also can change without impacting the intra-area routing protocol.
Reference:
Open Systems Interconnection (OSI) Routing Protocol
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/osi_rout.htm
Q2
In IS-IS, what network type identifies a LAN interface?A. broadcastB. point-to-pointC. pseudo-nodeD. non-broadcastE. point-to-multipoint
Ans: A
Explanation: The types of networks that IS-IS defines include Point-to-point networks and Broadcast
networks.
Reference: Cisco, Introduction to Intermediate, System-to-Intermediate System Protocol
http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/insys_wp.htm
Incorrect Anss
B: Point-to-point networks, such as serial lines, connect a single pair of routers.
C: A Designated Intermediate System (DIS) creates a pseudonode (a virtual node), and all the routers
on a LAN, including the DIS, form an adjacency with the pseudonode instead of forming n*(n-1)
order adjacencies with each other in a full mesh. DIS are not used by default however.
D: Non-broadcast is not used by IS-IS.
E: Point-to-multipoint is not used by IS-IS.
Q3
What is the metric used by Cisco routers on outgoing IS-IS interfaces?
You have just purchased a Cisco router, and have configured the outgoing interface with IS-IS. What
metric does that interface use?A. delayB. errorC. defaultD. expenseE. bandwidth
Ans: C
Explanation: The default metric used on Cisco IOS for IS-IS is the default (cost) metric and not
delay.
Q4
In the IS-IS routing protocol, what metric is supported exclusively by the Cisco IOS?A. DefaultB. DelayC. ExpenseD. Error
Ans: A
Explanation:
The original IS-IS specification defines four different types of metrics. Cost, being the default metric, is
supported by all routers. Delay, expense, and error are optional metrics. The delay metric measures
transit delay, the expense metric measures the monetary cost of link utilization, and the error metric
measures the residual error probability associated with a link.
The Cisco implementation uses cost only. If the optional metrics were implemented, there would be a
link-state database for each metric and SPF would be run for each link-state database.
and typically is assigned by a network administrator. Any single link can have a maximum value of 64,
and path links are calculated by summing link values. Maximum metric values were set at these levels
to provide the granularity to support various link types while at the same time ensuring that the shortestpath
algorithm used for route computation will be reasonably efficient. IS-IS also defines three optional
metrics (costs): delay, expense, and error.
Reference:
http://www.cisco.com/en/US/tech/ CK3 65/ CK3 81/technologies_white_paper09186a00800a3e6f.shtml
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