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MCQeasy
Which IS-IS TLV is used to carry IPv6 reachability information?
A.TLV 135
B.TLV 236
C.TLV 232
D.TLV 242
AnswerB
TLV 236 is IPv6 Reachability.
Why this answer
TLV 236 (IPv6 Reachability) carries IPv6 prefixes and associated metrics.
75 of 125 questions · Page 1/2 · Spcor Networking topic · Answers revealed
Which IS-IS TLV is used to carry IPv6 reachability information?
TLV 236 is IPv6 Reachability.
Why this answer
TLV 236 (IPv6 Reachability) carries IPv6 prefixes and associated metrics.
In an OSPF network, an engineer wants to reduce the size of the routing table and prevent external routes from being advertised into an area. Which area type should be configured?
Stub area blocks type 5 LSAs; uses default route to the ABR.
Why this answer
A stub area does not allow AS-external LSAs (type 5), reducing routing table size. NSSA allows limited external routes via type 7 LSAs.
In BGP, what is the purpose of the ORIGINATOR_ID attribute in a route reflector environment?
ORIGINATOR_ID is used to detect and avoid loops.
Why this answer
ORIGINATOR_ID is set by the route reflector to identify the originator of the route. It is used to prevent loops in iBGP.
Which IS-IS TLV is used to carry Traffic Engineering (TE) information such as link bandwidth and TE metric in modern SP networks?
Correct. TLV 22 carries extended IS reachability with sub-TLVs for TE.
Why this answer
IS-IS TE extensions use sub-TLVs within the extended IS reachability TLV (type 22). Specifically, TLV 135 (extended IP reachability) carries wide metrics, but TE information is carried in the extended IS reachability TLV (type 22) with sub-TLVs. The question asks for the TLV that carries TE info; the correct answer is the extended IS reachability TLV (type 22).
An engineer is configuring IS-IS fast convergence. Which mechanism provides sub-second failure detection independently of the routing protocol?
BFD provides sub-second failure detection.
Why this answer
BFD (Bidirectional Forwarding Detection) provides fast failure detection at the link layer, triggering routing protocol convergence.
A service provider is deploying BGP PIC (Prefix Independent Convergence) to improve convergence after a link failure. Which mechanism does BGP PIC leverage to achieve fast failover?
Correct. BGP PIC pre-installs backup paths for prefix-independent convergence.
Why this answer
BGP PIC uses backup paths that are pre-installed in the RIB/FIB. When the primary path fails, traffic is immediately switched to the backup path without waiting for BGP re-convergence.
An ISP is deploying BGP confederations to reduce iBGP mesh requirements. Which of the following statements about BGP confederations are true? (Choose two.)
Next-hop is not changed; it remains the same as iBGP.
Why this answer
BGP confederations divide an AS into sub-ASes. eBGP-like behavior is used between sub-ASes, but the AS_PATH length calculation treats the confederation as a single AS. The sub-AS number is appended to the AS_PATH with a special type code, but the AS_PATH length for best path selection ignores confederation segments.
A service provider is implementing 6PE to carry IPv6 traffic over an existing MPLS IPv4 core. Which BGP extension is required on the provider edge (PE) routers to exchange IPv6 prefixes with an IPv4 next-hop?
Correct. 6PE uses MP-BGP to advertise IPv6 prefixes with an IPv4 next-hop.
Why this answer
6PE uses BGP multiprotocol extensions (MP-BGP) with the IPv6 Address Family Identifier (AFI) and subsequent AFI (SAFI) to carry IPv6 prefixes. The next-hop is encoded as an IPv4 address using the 'next-hop' attribute with an IPv4 address. This is done via MP_REACH_NLRI for IPv6 with an IPv4 next-hop.
In BGP route selection, which attribute is considered before LOCAL_PREF?
Weight is checked first; it is Cisco proprietary.
Why this answer
BGP route selection starts with the highest weight (Cisco proprietary), then highest LOCAL_PREF, then locally originated routes.
Totally stubby blocks all inter-area (Type 3) except default, and all external (Type 4/5).
Why this answer
Totally stubby area blocks Type 4 (ASBR Summary) and Type 5 (External) LSAs, and also Type 3 (Summary) LSAs except for the default route.
VPNv6 unicast carries IPv6 VPN prefixes.
Why this answer
6VPE uses the VPNv6 address family (or IPv6 labeled unicast with VPN extensions) to carry IPv6 prefixes with VPN-IPv6 addresses.
In an IS-IS network, a router has a NET of 49.0001.1921.6800.1001.00. What does the '00' at the end represent?
SEL is always 00 for IS-IS.
Why this answer
The last byte '00' is the SEL (NSAP Selector), which is always '00' for IS-IS routing.
In IS-IS, what is the purpose of the System ID portion of the NET address?
Correct; System ID is unique per router in the area.
Why this answer
The NET (Network Entity Title) consists of AFI, Area ID, System ID, and SEL. The System ID uniquely identifies a router within an area.
Which OSPF area type does not allow external routes (Type 5 LSAs) but does allow inter-area routes and can have a default route injected?
Stub areas block Type 5 and have a default.
Why this answer
A stub area blocks Type 5 LSAs, and a default route is injected for external destinations.
An SP is implementing IPv6 transition using MAP-T. Which encapsulation method does MAP-T use?
MAP-T uses translation in the data plane.
Why this answer
MAP-T (Mapping of Address and Port using Translation) uses IPv4-IPv6 translation (stateless NAT64-like) at the customer edge, not encapsulation.
An engineer is designing an iBGP route reflector topology to improve scalability. Which two statements about BGP route reflectors are correct?
Originator-id is set by the RR and checked to avoid loops.
Why this answer
Route reflectors use cluster-id to detect loops and originator-id to prevent advertisement back to the originator. The non-client mesh requirement is eliminated with route reflectors.
Which three BGP communities are standardized and commonly used for inter-AS traffic engineering? (Choose three.)
Prevents route from being advertised to any eBGP peer.
Why this answer
Standard BGP communities include NO_EXPORT (0xFFFFFF01), NO_ADVERTISE (0xFFFFFF02), and LOCAL_AS (0xFFFFFF03). NO_EXPORT prevents advertisement to any eBGP peer; NO_ADVERTISE prevents advertisement to any peer; LOCAL_AS prevents advertisement outside the local AS.
Which BGP attribute is locally significant and used to influence outbound traffic from an AS?
LOCAL_PREF influences outbound traffic.
Why this answer
LOCAL_PREF is used to influence the path selection for outbound traffic within the AS, with higher preference preferred.
Which BGP attribute influences inbound traffic to an AS by affecting the path selection of eBGP peers?
MED is used to influence inbound traffic.
Why this answer
MED (Multi-Exit Discriminator) is used to influence inbound traffic by suggesting to a neighbor AS which path to use.
Which three BGP attributes are considered in the route selection process before comparing MED? (Choose three.)
Highest weight is first in selection.
Why this answer
The order: weight, local pref, originate (locally originated), AS_PATH length, ORIGIN, MED. So weight, local pref, and AS_PATH length are before MED.
In BGP route selection, which attribute is considered before the MED when comparing routes from different ASes?
ORIGIN (IGP, EGP, incomplete) is compared before MED.
Why this answer
The BGP best path selection order is: weight, local pref, originated locally, AS_PATH length, ORIGIN, MED, etc. MED is considered after ORIGIN.
Which three BGP attributes are considered before the MED in the BGP best path selection process?
Weight is first in order.
Why this answer
Weight, local preference, and AS_PATH length are considered before MED. ORIGIN is also before MED but AS_PATH is longer.
In a BGP confederation, which AS number is used in the AS_PATH to prevent loops within the confederation?
Private AS numbers are used within the confederation.
Why this answer
Confederation uses private AS numbers (from 64512 to 65535) for sub-ASs, and these are prepended to the AS_PATH but not shown to external peers.
A service provider is designing an OSPF network for both IPv4 and IPv6. Which two features are supported by OSPFv3 but not by OSPFv2? (Choose two.)
OSPFv3 is designed for IPv6.
Why this answer
OSPFv3 runs over IPv6, supports multiple instances per link, and uses link-local addresses. OSPFv2 does not have these.
Which BGP mechanism can reduce the number of iBGP sessions in a large SP network while preventing routing loops?
Route reflectors reduce iBGP sessions and use loop prevention mechanisms.
Why this answer
Route reflectors allow iBGP speakers to advertise routes learned from other iBGP peers, reducing full mesh requirements, and use cluster-id and originator-id to prevent loops.
In OSPFv3, what change was introduced compared to OSPFv2 for supporting IPv6?
Correct; OSPFv3 uses IPv6 link-local addresses for neighbor communication.
Why this answer
OSPFv3 runs per-link instead of per-subnet, uses link-local addresses for neighbor discovery, and separates the protocol from addressing by using LSAs with IPv6 prefix information.
In IS-IS, which type of router is responsible for routing between different areas and also maintains a Level 1 Link State Database?
L1/L2 routers participate in both levels.
Why this answer
L1/L2 routers perform both intra-area and inter-area routing, maintaining both L1 and L2 LSDBs.
A service provider is implementing BGP PIC (Prefix Independent Convergence) for its core network. Which mechanism does BGP PIC primarily rely on to achieve fast convergence?
BGP PIC precomputes and installs backup paths in FIB.
Why this answer
BGP PIC uses precomputed backup paths (e.g., via BGP PIC edge or BGP add-path) to switch traffic upon failure without waiting for BGP convergence.
In OSPFv3, which of the following is true about the protocol's operation?
OSPFv3 adjacencies are formed over links, not IP subnets.
Why this answer
OSPFv3 runs per-link, not per-subnet; it uses link-local addresses for adjacencies and floods LSA types specific to IPv6.
Which OSPF area type can import external routes as Type 7 LSAs?
NSSA allows external routes as Type 7 LSAs.
Why this answer
NSSA (Not-So-Stubby Area) allows the import of external routes as Type 7 LSAs, which are translated to Type 5 at the ABR.
A service provider wants to enable fast convergence for OSPF networks. Which feature should be enabled to detect link failures in sub-second time?
BFD provides sub-second failure detection.
Why this answer
BFD (Bidirectional Forwarding Detection) provides fast failure detection for routing protocols like OSPF. OSPF can be configured to use BFD for sub-second convergence.
An ISP is implementing 6PE for IPv6 transport over MPLS. Which two conditions are required for 6PE to work? (Choose two.)
BGP must carry IPv6 address family.
Why this answer
6PE requires BGP to carry IPv6 prefixes with an IPv4 next-hop (MPLS label), and the core MPLS network must support IPv4 LSPs.
An SP engineer is configuring IS-IS on a router and specifies a NET address of 49.0001.1921.6800.1001.00. What does the '00' at the end represent?
SEL identifies the network service user; 00 is for the routing protocol.
Why this answer
The last two octets of an IS-IS NET address represent the SEL (NSAP Selector), which is always 00 for a router.
A service provider is designing an OSPF network with multiple areas. Which two area types prevent Type 5 LSAs from entering the area (choose two)?
Stub area blocks Type 5 LSAs.
Why this answer
Stub and NSSA both block Type 5 LSAs. However, NSSA allows Type 7 LSAs which are translated to Type 5 at the ABR.
Which IS-IS metric type is required for traffic engineering and segment routing?
Wide metrics support larger values and are used for TE and segment routing.
Why this answer
IS-IS wide metrics (TLV 22 and 135) use 24-bit or 32-bit values, allowing higher link costs needed for TE. Narrow metrics are limited to 6 bits.
An SP network is migrating from IS-IS narrow metrics to wide metrics. What is a key advantage of using wide metrics?
Wide metrics allow larger values and TE extensions.
Why this answer
Wide metrics support values up to 2^24-1 (16,777,215) and allow Traffic Engineering (TE) metrics, unlike narrow metrics which are limited to 6 bits (max 63).
A service provider is implementing Segment Routing in an IS-IS network. Which TLV is used to advertise the Segment Routing Global Block (SRGB)?
TLV 242 is the Router Capability TLV used for SRGB advertisement.
Why this answer
The IS-IS Router Capability TLV (242) carries sub-TLVs including the SR Capabilities sub-TLV that advertises the SRGB.
Which TWO of the following are types of OSPF stub areas? (Choose two.)
Correct. Blocks Type 5 LSAs.
Why this answer
OSPF defines several stub area types. A stub area blocks Type 5 LSAs. A totally stubby area (Cisco proprietary) blocks Type 3, 4, and 5 except for a default route.
NSSA (Not-So-Stubby Area) allows external routes via Type 7 LSAs.
An SP is deploying NAT64 to allow IPv6-only clients to access IPv4 servers. Which address translation mechanism is used by NAT64 to map IPv6 addresses to IPv4 addresses?
Correct. NAT64 uses a prefix (64:ff9b::/96) to embed IPv4 addresses.
Why this answer
NAT64 uses a well-known prefix (64:ff9b::/96) to embed IPv4 addresses into IPv6 addresses. The IPv4 address is appended to the prefix, creating an IPv6 address that represents the IPv4 destination.
Type 10 carries TE information within an area.
Why this answer
OSPF uses opaque LSAs to carry TE information. Type 10 (area-local) and Type 11 (AS-scoped) opaque LSAs are used for TE. Type 9 is link-local.
An engineer is configuring IS-IS in a service provider network. The network uses wide metrics for traffic engineering. Which TLV is mandatory for IS-IS to carry traffic engineering (TE) information in accordance with RFC 5305?
TLV 22 carries TE information including link attributes.
Why this answer
TLV 22 (Extended IS Reachability) is the mandatory TLV for IS-IS TE, defined in RFC 5305.
In IS-IS, which type of LSP is used to advertise prefix information for IPv4 and IPv6 in a modern SP network that supports traffic engineering?
TLV 135 carries IPv4 prefixes with wide metrics.
Why this answer
TLV 135 for IPv4 (extended IP reachability) and TLV 236 for IPv6 (IPv6 reachability) are used in IS-IS for prefix advertisement.
In IS-IS, a router is configured as L1 only. Which statement is true regarding its routing table?
Correct. The L1/L2 router advertises a default route into L1 area.
Why this answer
An L1 router only knows routes within its own area. It uses the closest L1/L2 router as a default route to reach other areas. The L1/L2 router leaks a default route into the L1 area.
Which THREE of the following are valid BGP extended community attributes? (Choose three.)
SoO is an extended community for loop prevention.
Why this answer
Route Target (RT), Route Origin (RO), and Site of Origin (SoO) are well-known extended communities. The Color extended community is also valid, but the question asks for three; the correct three are RT, RO, and SoO. The standard community is 32-bit, not extended.
A service provider is deploying IPv6 transition mechanisms. Which three technologies use encapsulation over an IPv4 network? (Choose three.)
6VPE encapsulates IPv6 VPN traffic over MPLS.
Why this answer
6PE, 6VPE, and 6rd encapsulate IPv6 packets over IPv4; MAP-T uses translation, not encapsulation.
Which BGP attribute is used to influence inbound traffic to a specific AS by indicating the preferred path?
MED is used to influence inbound traffic by indicating the preferred entry point.
Why this answer
MED (Multi-Exit Discriminator) is used to influence inbound traffic from a neighboring AS; lower MED is preferred.
Which IS-IS level is used for routing within an area?
L1 is used for routing within a single area.
Why this answer
IS-IS uses Level 1 (L1) for intra-area routing and Level 2 (L2) for inter-area routing.
An SP network is running OSPFv3 for IPv6 and needs to support traffic engineering extensions for RSVP-TE. Which three statements about OSPFv3 TE extensions are true?
TLV 1 is the Router Address TLV used in OSPF TE.
Why this answer
OSPFv3 uses Opaque LSA types 9, 10, and 11 for TE, with Type 10 carrying TE information link-state. OSPFv3 TE requires the OSPFv3 process to be configured for TE.
Type 10 is area-scoped opaque, used for TE.
In OSPF, which type of area does not allow external routes and only accepts a default route?
Stub areas block Type 5 LSAs and use a default route.
Why this answer
A stub area blocks Type 5 LSAs and injects a default route; it does not accept external routes from other areas.
An SP network is implementing BGP PIC (Prefix Independent Convergence) for fast failover. What is the primary mechanism used by BGP PIC to achieve sub-second convergence?
Correct. BGP PIC installs a backup path so that upon failure, traffic is immediately switched to the backup.
Why this answer
BGP PIC uses a backup path (often a pre-computed alternate path) that is installed in the FIB along with the primary path. Upon failure of the primary path, traffic is switched to the backup path without waiting for BGP convergence.
An SP network is using IS-IS and wants to achieve fast convergence using BFD. Which two statements about BFD in IS-IS are correct?
BFD provides fast detection, typically less than 1 second.
Why this answer
BFD provides fast failure detection (sub-second) and is configured under the interface. IS-IS does not require BFD for normal operation; it's an enhancement.
In IS-IS, which type of metric uses 24 bits (wide) to allow higher link bandwidth values and is required for TE support?
Correct. Wide metrics are 24 bits and support TE.
Why this answer
IS-IS originally used narrow metrics (6 bits), but wide metrics (24 bits) were introduced in TLV 135 and 22 to support higher values and TE. Wide metrics are required for traffic engineering.
Which BGP attribute is used to influence inbound traffic to an AS by indicating the preferred path into the AS?
Correct. MED is used to influence inbound traffic.
Why this answer
The MED (Multi-Exit Discriminator) is used to influence inbound traffic from neighboring ASes. It is advertised to eBGP peers and is compared when multiple paths to the same prefix exist from the same neighboring AS.
In IS-IS, what is the result of configuring wide metrics on all interfaces?
Wide metrics support higher values, essential for TE.
Why this answer
Wide metrics (24-bit or 32-bit) allow values up to 16,777,215 or higher, enabling TE and faster convergence with precise metric adjustments.
An SP network engineer configures IS-IS with wide metrics. Which statement is true about IS-IS wide metrics compared to narrow metrics?
Wide metrics use TLV 135 and 236 for TE.
Why this answer
Wide metrics use a 24-bit field, allowing values up to 16,777,215, and support TE extensions and segment routing.
An SP engineer configures IS-IS fast convergence mechanisms. Which three techniques help achieve sub-second convergence in IS-IS?
iSPF reduces SPF recomputation.
Why this answer
BFD provides fast failure detection, PRC recalculates only affected routes, and SPF incremental (iSPF) reduces SPF computation. LFA provides fast reroute.
A service provider is implementing BGP route reflectors to scale iBGP. Which THREE mechanisms are used to prevent routing loops in a route reflector topology? (Choose three.)
Correct. CLUSTER_LIST tracks clusters to prevent loops.
An SP is deploying IS-IS fast convergence. Which mechanism triggers an immediate SPF computation when a neighbor fails?
BFD detects failures quickly and triggers convergence.
Why this answer
BFD (Bidirectional Forwarding Detection) provides sub-second failure detection and triggers SPF/PRC.
An SP network uses MPLS to provide IPv6 connectivity over an IPv4 backbone using 6PE. Which BGP extension is required on the provider edge routers to exchange IPv6 prefixes with an IPv4 next-hop?
MP-BGP with IPv6 unicast address family allows carrying IPv6 routes with IPv4 next-hop.
Why this answer
6PE uses BGP multiprotocol extensions (MP-BGP) with an AFI of 2 (IPv6) and SAFI of 1 (unicast), and the next-hop is encoded as an IPv4 address using the 'next-hop' attribute.
In BGP confederation, which attribute is used to prevent loops between sub-ASes?
Confederation AS_PATH prevents loops within confederation.
Why this answer
The confederation AS_PATH (AS_CONFED_SEQUENCE and AS_CONFED_SET) is used to track the path within the confederation, and loop detection checks this attribute.
In BGP, which attribute is used to prevent routing loops when route reflectors are deployed?
Originator ID identifies the originator of a route within an AS.
Why this answer
Originator ID is used by route reflectors to prevent loops. If a router receives a route with its own router ID as originator, it discards it.
In OSPFv3 (for IPv6), which of the following statements is true regarding OSPFv3 packet format and authentication?
OSPFv3 uses IPsec AH or ESP for authentication and confidentiality.
In BGP route selection, if two routes have the same weight, local preference, and are both locally originated, which attribute is considered next?
Shorter AS_PATH is preferred.
Why this answer
After weight, local pref, and locally originated, BGP compares AS_PATH length (shorter is preferred).
An ISP is implementing BGP PIC (Prefix Independent Convergence) for edge routers. Which BGP feature must be enabled to support PIC for core-facing failures?
This allows installation of backup paths for PIC.
Why this answer
BGP PIC relies on installing a backup path in the FIB. For core-facing failures, BGP Fast External Fallover and BGP PIC with backup paths are used; specifically, 'bgp additional-paths install' is needed to install backup paths.
An SP is deploying IS-IS fast convergence using Partial Route Computation (PRC). Under which condition does PRC occur?
PRC handles prefix changes only.
Why this answer
PRC is triggered when a prefix changes but the topology remains unchanged. It recalculates only the affected prefixes, not the entire SPF tree.
A service provider is configuring BGP route reflectors to scale iBGP. Which two mechanisms are used to prevent routing loops in a route reflector environment? (Choose two.)
Correct. CLUSTER_LIST contains the cluster-ids and prevents loops.
Why this answer
Which BGP attribute is used to prefer a specific entry point into an AS when multiple ASBRs are advertising the same prefix to a neighboring AS?
MED is exchanged between ASes to influence inbound traffic.
Why this answer
MED (Multi-Exit Discriminator) is used to influence the inbound traffic by suggesting the preferred entry point.
A service provider is designing an OSPF network with multiple areas. Which TWO area types allow external routes (Type 5 LSAs) to be injected into the area? (Choose two.)
Standard area (non-stub) accepts Type 5 LSAs.
Why this answer
Standard areas and the backbone area (Area 0) allow Type 5 LSAs. Stub, totally stubby, and NSSA do not accept Type 5 LSAs (NSSA converts Type 7 to Type 5 at ABR, but internally uses Type 7).
Correct. 6VPE uses AFI=2, SAFI=128, and the next-hop is an IPv4 address mapped to IPv6.
Which BGP attribute is used to influence inbound traffic to an AS by advertising a preferred path to a neighbor AS?
MED is used to influence inbound traffic from a neighbor AS.
Why this answer
MED (Multi-Exit Discriminator) is sent to a neighboring AS to suggest the best entry point into the local AS. Lower MED is preferred.
A service provider deploys BGP route reflectors in the core. Which mechanism prevents routing loops within the route reflector cluster?
Originator-id identifies the originator; if a router receives its own originator-id, it discards the route.
Why this answer
The originator-id attribute is set by the route reflector to the router-id of the originating router, preventing loops by checking if the originator-id matches the local router-id.
A service provider wants to provide IPv6 connectivity over an existing MPLS IPv4 core using BGP extensions. Which technology should be used?
6PE uses BGP to carry IPv6 over MPLS with IPv4 next-hop.
Why this answer
6PE (IPv6 Provider Edge) uses BGP to carry IPv6 prefixes with an IPv4 next-hop over an MPLS core, avoiding the need for IPv6 in the core.
Which OSPF network type elects a Designated Router (DR) and Backup Designated Router (BDR) to reduce the number of adjacencies on a multi-access segment?
Broadcast elects DR and BDR.
Why this answer
Broadcast network type uses DR/BDR election. Point-to-point and NBMA do not elect DR/BDR (NBMA does elect DR/BDR but is less common).
Which OSPF adjacency type requires DR/BDR election on a multi-access network?
Broadcast networks use DR/BDR election.
Why this answer
On broadcast and NBMA networks, OSPF elects a Designated Router (DR) and Backup Designated Router (BDR) to reduce adjacencies.
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