300-420 — 300-420 ENSLD: Designing Cisco Enterprise Networks v1.1
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300-420 ENSLD: Designing Cisco Enterprise Networks v1.1 (300-420) Practice Questions

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150 questions
June 19, 2026 updated
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Sample Questions (15 of 150 shown)

Q1
When designing OSPF with 60 remote sites, why is single-area (area 0) avoided?
  1. OSPF cannot run with >50 routers per area
  2. LSDB size, SPF cost, and flooding grow with area, hurting convergence
  3. Single-area cannot do ECMP
  4. Single-area requires manual neighbor statements
✓ Correct Answer: B
Multi-area OSPF limits LSDB size, contains SPF recalculation, and bounds LSA flooding. Hierarchy via ABRs scales the design.
Q2
Which OSPF area blocks Type 5 but allows Type 7 LSAs?
  1. Stub area
  2. Totally stubby area
  3. NSSA
  4. Backbone area
✓ Correct Answer: C
NSSA blocks Type 5 LSAs but permits Type 7 LSAs from ASBR inside the NSSA. The ABR translates Type 7 to Type 5 for other areas.
Q3
On which routers should OSPF inter-area summarization be configured?
  1. Every internal router
  2. ABRs connecting the area to backbone
  3. ASBR redistributing external routes
  4. DR/BDR
✓ Correct Answer: B
OSPF inter-area summarization uses 'area range' on ABRs, collapsing Type 3 LSAs. ASBRs use 'summary-address' for external routes.
Q4
Which mechanism fixes a non-backbone area that lost connection to Area 0?
  1. Configure a virtual link across a transit area
  2. Convert to stub area
  3. Convert to NSSA with default-information
  4. GRE tunnel between random routers
✓ Correct Answer: A
OSPF virtual links through a transit area logically extend the backbone. They are a last-resort fix per Cisco design guides.
Q5
Which EIGRP design technique limits query scope during topology change?
  1. Increase hello/hold timers
  2. Stub routers and route summarization at hierarchical boundaries
  3. Enable authentication
  4. Switch to named mode
✓ Correct Answer: B
EIGRP queries are bounded by stub routers (which don't propagate queries) and summarization (router with summary replies immediately).
Q6
Which BGP scaling technique replaces iBGP full-mesh?
  1. BGP confederations
  2. Route reflectors
  3. Peer groups
  4. Soft reconfiguration
✓ Correct Answer: B
Route reflectors break the iBGP full-mesh requirement by reflecting routes from non-client to clients and between clients.
Q7
Which BGP attribute influences inbound traffic from a specific upstream provider?
  1. Local Preference
  2. MED (Multi-Exit Discriminator)
  3. AS-path prepending
  4. Origin code
✓ Correct Answer: B
MED is advertised to a neighboring AS to influence how it selects entry points. Providers often expose communities mapping to MED.
Q8
Primary design risk of mutual redistribution between OSPF and EIGRP at two boundaries?
  1. Increased SPF runtime
  2. Routing loops from mutual redistribution
  3. Incompatible authentication
  4. Cannot advertise IPv6
✓ Correct Answer: B
Mutual redistribution at two or more boundaries can re-inject routes into the origin protocol. Use route tags, distribute lists, or AD changes.
Q9
Which IPv6 transition mechanism lets IPv6-only hosts reach IPv4-only servers?
  1. 6to4 tunneling
  2. ISATAP
  3. NAT64 with DNS64
  4. 6PE
✓ Correct Answer: C
NAT64+DNS64 lets IPv6-only clients reach IPv4-only servers. DNS64 synthesizes AAAA records from A records.
Q10
Which statement about OSPFv3 is correct?
  1. OSPFv3 uses global IPv6 addresses for packets
  2. OSPFv3 peers identified by IPv4 router-id
  3. OSPFv3 cannot coexist with OSPFv2 on same link
  4. OSPFv3 uses TCP
✓ Correct Answer: B
OSPFv3 still uses a 32-bit Router ID in dotted-decimal. Packets use link-local IPv6 addresses.
Q11
Which BGP attribute is well-known mandatory and used for loop prevention?
  1. AS_PATH
  2. LOCAL_PREF
  3. MED
  4. COMMUNITY
✓ Correct Answer: A
AS_PATH lists ASes a route traversed, used for loop prevention (reject if own AS seen) and path selection (shorter preferred).
Q12
What is the recommended method to scale iBGP in a large enterprise?
  1. Route reflectors with multiple redundant clusters
  2. Single route reflector
  3. Full mesh
  4. Use only eBGP
✓ Correct Answer: A
Route reflectors in redundant clusters scale iBGP. Multiple RRs provide redundancy and load distribution.
Q13
What is BGP communities used for?
  1. Tagging routes for policy enforcement at AS boundaries
  2. Setting the next-hop
  3. Determining the best path
  4. Configuring routing metrics
✓ Correct Answer: A
BGP communities tag routes with attributes that upstream/downstream ASes can use for policy decisions like filtering or local preference setting.
Q14
Which addressing design practice conserves IPv4 space in enterprise networks?
  1. VLSM and private addressing with NAT
  2. Classful addressing
  3. Public addressing for all devices
  4. Using only /24 subnets
✓ Correct Answer: A
VLSM and RFC 1918 private addressing with NAT conserves IPv4 address space. Use the smallest subnet that fits the host requirement.
Q15
What is the recommended BGP design for a dual-homed enterprise to two ISPs?
  1. eBGP to both ISPs with AS-path prepending and MED for traffic engineering
  2. Static default routes only
  3. iBGP between ISPs
  4. OSPF with both ISPs
✓ Correct Answer: A
eBGP peering to both ISPs enables prefix advertisement control and traffic engineering using AS-path prepending, MED, and communities.

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