CCNA IP Connectivity: 97 practice questions
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CCNA IP Connectivity: 97 practice questions

CCNA 97 questions 12 shown free

12 of the 97 IP Connectivity questions in the Certsqill CCNA bank, shown in full below. Each one carries an explanation for every option, not just the correct one — the wrong answers are where the marks go.

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1. Static route — Administrative Distance 1 is lower than: Which route will the router prefer and why?

Medium
A router's routing table contains two routes to the 10.1.1.0/24 network: one learned via OSPF and one via a static route. Which route will the router prefer and why?
  1. Static route — Administrative Distance 1 is lower than OSPF's AD of 110 ✓
    Administrative distance decides which source wins when the same prefix is learned twice. A static route has AD 1 and OSPF has AD 110, so the lower AD static route is installed in the routing table.
  2. OSPF route — a dynamic protocol is more reliable than a static route
    Being dynamic or 'more reliable' does not decide preference; administrative distance does. A static route at AD 1 always beats an OSPF route at AD 110 for the same destination.
  3. OSPF route — its metric is lower than that of the competing static route
    Metric is only compared among routes from the same protocol, and AD is evaluated first; with different ADs, OSPF's cost is irrelevant against a static route.
  4. Both routes are installed and the router load-balances traffic across them
    Load balancing needs equal AD and equal metric; a static route at AD 1 and an OSPF route at AD 110 have different ADs, so only the lower-AD static route is installed.
The trap
Metric is only compared within the same protocol — administrative distance is compared across different routing sources (static vs OSPF, etc.)

When two routes to the same destination exist, administrative distance determines which is installed. Static routes have AD=1; OSPF has AD=110. Lower AD wins — the static route is preferred.

2. 10.10.10.0/24 via 192.168.1.3: Which route is used?

Hard
A router has the following routes in its table:
• 10.0.0.0/8 via 192.168.1.1
• 10.10.0.0/16 via 192.168.1.2
• 10.10.10.0/24 via 192.168.1.3
• 0.0.0.0/0 via 192.168.1.4
The router receives a packet destined for 10.10.10.5. Which route is used?
  1. 10.0.0.0/8 via 192.168.1.1
    10.0.0.0/8 does match 10.10.10.5 but is a /8 prefix, less specific than the /16 and /24 routes. Longest prefix match always selects the most specific (longest prefix length) route.
  2. 10.10.10.0/24 via 192.168.1.3 ✓
    Longest prefix match: the router selects the most specific route that matches the destination. 10.10.10.5 matches all four routes, but 10.10.10.0/24 (prefix length /24) is the longest, most specific match and is selected.
  3. 0.0.0.0/0 via 192.168.1.4
    The default route (0.0.0.0/0) matches all destinations but is a /0, the least specific possible match. It is only used when no more specific route exists.
  4. 10.10.0.0/16 via 192.168.1.2
    10.10.0.0/16 matches 10.10.10.5 and is more specific than /8 and /0, but /24 is even more specific. Longest prefix match selects /24 over /16.
The trap
The default route matches everything but is always the last resort — any more specific matching route wins over /0

Longest prefix match: the router always selects the route with the longest (most specific) matching prefix. 10.10.10.5 matches all four routes — /24 is the longest prefix and is selected.

3. ip route 0.0.0.0 0.0.0.0 203.0.113.1: Which command creates the correct default static route?

Easy
A branch office router needs to forward all traffic for destinations not in its routing table to the ISP router at 203.0.113.1. Which command creates the correct default static route?
  1. ip route 0.0.0.0 255.255.255.255 203.0.113.1
    A subnet mask of 255.255.255.255 means /32, which would create a host route to 0.0.0.0/32, not a default route matching all destinations. Default routes require mask 0.0.0.0.
  2. ip default-gateway 203.0.113.1
    'ip default-gateway' is used on Cisco switches (or in Layer 2 mode) to configure the gateway for management traffic; it does not configure a routing table entry on a router.
  3. ip route 0.0.0.0 0.0.0.0 203.0.113.1 ✓
    A default static route uses the network 0.0.0.0 with subnet mask 0.0.0.0, which matches all destinations. The next hop 203.0.113.1 sends all unmatched traffic to the ISP router.
  4. ip route 255.255.255.255 0.0.0.0 203.0.113.1
    255.255.255.255 is the broadcast address and is not the correct network address for a default route. The default route uses 0.0.0.0 as both the network address and the mask.
The trap
'ip default-gateway' is for switch management traffic; 'ip route 0.0.0.0 0.0.0.0' creates a router default route — different commands for different purposes

Default static route: 'ip route 0.0.0.0 0.0.0.0 <next-hop>'. The 0.0.0.0 network with 0.0.0.0 mask matches all destinations, creating a catch-all route of last resort.

4. ip route 192.168.10.0 255.255.255.0 10.0.0.2 111: Which command creates a floating static route as a backup fo

Medium
A router learns the 192.168.10.0/24 network via OSPF as its primary path. A backup path should be used only if the OSPF route is lost. Which command creates a floating static route as a backup for this network via next-hop 10.0.0.2?
  1. ip route 192.168.10.0 255.255.255.0 10.0.0.2
    Without specifying an AD, the static route uses default AD=1, so it would be preferred over the OSPF route (AD=110), making it the primary path rather than the backup.
  2. ip route 192.168.10.0 255.255.255.0 10.0.0.2 90
    AD=90 is lower than OSPF's AD=110 but higher than a normal static route (AD=1). It would still be preferred over OSPF, making it primary, not backup. A floating static route needs an AD higher than the primary protocol.
  3. ip route 192.168.10.0 255.255.255.0 10.0.0.2 255
    AD=255 means 'unreachable/unknown'; a route with AD=255 is never installed in the routing table. The floating static should use a usable AD higher than OSPF (>110) but not 255.
  4. ip route 192.168.10.0 255.255.255.0 10.0.0.2 111 ✓
    A floating static route uses an administrative distance higher than OSPF's default AD (110). AD=111 keeps the static route out of the table while the OSPF route exists; only when OSPF disappears does the AD=111 static route install as backup.
The trap
Floating static route must have AD HIGHER than the primary protocol's AD (higher number = lower preference) — not lower

A floating static route has an AD higher than the primary protocol's AD. Since OSPF is AD=110, the floating static must use AD > 110 (e.g., 111). The static route installs only when the OSPF route disappears.

5. 172.16.0.1 — the highest IP address on any loopback: Which IP address will OSPF use as the Router ID?

Medium
A Cisco router is configured with OSPF. The router has: Loopback0 with IP 10.0.0.1, Loopback1 with IP 172.16.0.1, GigabitEthernet0/0 with IP 192.168.1.1 (active), and no manually configured Router ID. Which IP address will OSPF use as the Router ID?
  1. 172.16.0.1 — the highest IP address on any loopback interface ✓
    OSPF picks its Router ID in order: a manual router-id, then the highest loopback IP, then the highest active interface IP. With no manual ID and loopbacks 10.0.0.1 and 172.16.0.1, the higher loopback 172.16.0.1 wins.
  2. 192.168.1.1 — the highest IP address on any active interface
    A physical interface IP is used only when no loopback exists. Because Loopback0 and Loopback1 are present, the highest loopback IP is chosen instead of 192.168.1.1.
  3. 10.0.0.1 — the first configured loopback becomes the Router ID
    The first loopback is not the rule; OSPF selects the highest loopback IP, and 172.16.0.1 is higher than 10.0.0.1, so 10.0.0.1 does not win.
  4. The Router ID cannot be set without manual configuration
    OSPF can always derive a Router ID from the priority order of manual, highest loopback, then highest active interface, so a manual configuration is not required here.
The trap
Loopback interfaces take priority over physical interfaces for OSPF Router ID — always highest loopback IP before highest physical IP

OSPF Router ID selection: (1) manually configured, (2) highest loopback IP, (3) highest active physical interface IP. Two loopbacks exist (10.0.0.1 and 172.16.0.1) → highest loopback is 172.16.0.1.

6. DR=R2, BDR=R4: Which router becomes the DR and which becomes the BDR?

Hard
Four OSPF routers share a common Ethernet segment. Their OSPF priorities are: R1=1, R2=100, R3=0, R4=50. Their Router IDs are: R1=1.1.1.1, R2=2.2.2.2, R3=3.3.3.3, R4=4.4.4.4. Which router becomes the DR and which becomes the BDR?
  1. DR=R3, BDR=R2
    R3 has OSPF priority 0, and a priority of 0 means the router will never become DR or BDR. R3 is permanently a DROTHER on this segment.
  2. DR=R2, BDR=R4 ✓
    DR/BDR election: highest OSPF priority wins. R2 has priority 100 (highest) so it becomes DR. R3 has priority 0 and is never eligible. Of the rest, R4 (priority 50) beats R1 (priority 1), so R4 becomes BDR.
  3. DR=R4, BDR=R2
    R4 has priority 50, which is lower than R2's priority 100. R2 becomes DR (highest priority), not R4, and R4 becomes BDR as the next highest eligible.
  4. DR=R2, BDR=R1
    R4 (priority 50) has higher priority than R1 (priority 1), so R4 becomes BDR, not R1. Priority is compared after DR selection to determine the BDR.
The trap
OSPF priority 0 means NEVER DR/BDR regardless of Router ID — priority takes precedence over Router ID in the election

OSPF DR/BDR election on multiaccess networks: highest priority wins DR. Priority 0 = ineligible. R2 (priority 100) = DR; R3 eliminated (priority 0); R4 (priority 50) > R1 (priority 1) → R4 = BDR.

7. An MTU mismatch between the two OSPF neighbors: What is the most likely cause?

Medium
A network engineer runs 'show ip ospf neighbor' and sees that a neighbor is stuck in the EXSTART state. What is the most likely cause?
  1. A hello interval mismatch between the OSPF neighbors
    A hello interval mismatch stops the adjacency from forming at all, leaving neighbors in INIT or invisible, rather than letting them reach and stall in EXSTART.
  2. Mismatched OSPF area IDs on both interfaces
    An area ID mismatch also blocks adjacency before 2-WAY, so neighbors never advance to EXSTART, which occurs only after the basic parameters already match.
  3. An MTU mismatch between the two OSPF neighbors ✓
    EXSTART is where OSPF negotiates master/slave and begins DBD exchange. An MTU mismatch causes the larger DBD packets to be dropped by the smaller-MTU side, so the neighbors never move past EXSTART.
  4. The connecting interfaces are passive OSPF interfaces
    A passive interface suppresses hellos entirely, so no neighbor is discovered; a neighbor stuck in EXSTART has already exchanged hellos and reached 2-WAY, ruling this out.
The trap
OSPF hello/area mismatches prevent neighbors from forming at all; MTU mismatch allows initial neighbor formation but blocks database exchange (stuck in ExStart)

EXSTART is the state where OSPF neighbors negotiate master/slave for database exchange using DBD packets. MTU mismatch causes DBD packets to exceed one side's MTU and be dropped — preventing progression to EXCHANGE and beyond.

8. 1: What is the OSPF cost of a 1 Gbps (1000 Mbps) Ethernet interface?

Medium
A router running OSPF uses the default reference bandwidth of 100 Mbps. What is the OSPF cost of a 1 Gbps (1000 Mbps) Ethernet interface?
  1. 10
    A cost of 10 would correspond to a 10 Mbps interface (100/10=10). For 1 Gbps the math is 100/1000=0.1, which rounds up to the minimum of 1.
  2. 1000
    1000 would result if the formula were inverted (bandwidth/reference). OSPF cost is reference/bandwidth, not the inverse, so for 1 Gbps it is 100/1000 = 0.1, giving cost 1.
  3. 100
    100 is the OSPF cost of a 1 Mbps interface (100/1=100), not a 1 Gbps interface. At 1 Gbps the cost is 1, the minimum value.
  4. 1 ✓
    OSPF cost = reference bandwidth / interface bandwidth = 100 Mbps / 1000 Mbps = 0.1. Since OSPF cost has a minimum of 1, the result rounds up to 1. That is why 100 Mbps, 1 Gbps, and 10 Gbps all show cost 1 by default, and why the reference bandwidth should be raised for modern networks.
The trap
OSPF cost has a minimum of 1 — any bandwidth faster than the reference bandwidth also costs 1, which breaks OSPF path selection on modern networks without tuning reference bandwidth

OSPF cost = reference bandwidth / interface bandwidth = 100 Mbps / 1000 Mbps = 0.1, rounded to minimum of 1. This is why OSPF reference bandwidth must be updated for networks with Gigabit+ interfaces.

9. router ospf 1 → network 0.0.0.0 255.255.255.255 area 0 →: Which configuration achieves this?

Medium
A router has three interfaces: G0/0 (10.1.1.1/24), G0/1 (10.1.2.1/24), and G0/2 (192.168.1.1/24). The network administrator wants OSPF to advertise all three networks but suppress hello messages only on G0/2 (which connects to a customer network with no OSPF routers). Which configuration achieves this?
  1. router ospf 1 → network 0.0.0.0 255.255.255.255 area 0 → passive-interface GigabitEthernet0/2 ✓
    'network 0.0.0.0 255.255.255.255 area 0' enables OSPF on all interfaces, and 'passive-interface G0/2' suppresses hellos on G0/2 while still advertising its prefix. The interface participates in OSPF routing without sending hellos.
  2. router ospf 1 → network 10.1.0.0 0.0.255.255 area 0 → network 192.168.1.0 0.0.0.255 area 0
    This enables OSPF on all three interfaces but does not suppress hellos on G0/2. Without passive-interface, G0/2 keeps sending hellos to the customer network, which is unnecessary and exposes OSPF information.
  3. router ospf 1 → network 0.0.0.0 255.255.255.255 area 0 → no ip ospf hello on G0/2
    'no ip ospf hello' is not a valid Cisco IOS command. The correct way to suppress hellos on an interface is 'passive-interface <interface>'.
  4. router ospf 1 → network 10.1.1.0 0.0.0.255 area 0 → network 10.1.2.0 0.0.0.255 area 0 → no network 192.168.1.0 area 0
    'no network' removes G0/2 from OSPF entirely, so its prefix would not be advertised. The requirement is to advertise all three prefixes but suppress hellos on G0/2 only.
The trap
Passive-interface suppresses OSPF hellos but still advertises the subnet — removing from the 'network' statement removes the subnet from OSPF entirely

OSPF passive-interface advertises the interface's prefix into OSPF but suppresses hello messages — perfect for stub interfaces (customer-facing, server farms) where no OSPF neighbors exist but the network should be reachable.

10. 192.168.1.254: What is the default gateway that hosts on the 192.168.1.0/24 network should configure?

Medium
Two routers (R1 and R2) are configured with HSRP for the 192.168.1.0/24 subnet. R1 has HSRP priority 110 and R2 has priority 100. The HSRP virtual IP is 192.168.1.254. What is the default gateway that hosts on the 192.168.1.0/24 network should configure?
  1. R1's interface IP — the active HSRP router's real interface address
    Using R1's real interface IP as the gateway is unsafe, because if R1 fails that address disappears; the virtual IP stays reachable regardless of which physical router is active.
  2. 192.168.1.254 — the shared HSRP virtual IP address for the subnet ✓
    Hosts point their default gateway at the HSRP virtual IP 192.168.1.254, not at either router's real interface. The active router R1 (priority 110) answers for the virtual IP and virtual MAC.
  3. Both R1 and R2 interface IPs in a dual-gateway configuration
    HSRP exists to present one virtual IP that survives a router failure, so hosts use a single virtual gateway rather than both physical interface IPs in a dual-gateway setup.
  4. R2's interface IP — the standby router used as the load-balancing gateway
    In standard HSRP only the active router forwards traffic; the standby R2 with lower priority does not carry traffic and takes over only if R1 fails.
The trap
HSRP hosts configure the VIRTUAL IP — never the actual router interface IPs. The virtual IP survives individual router failures

Hosts configure the HSRP virtual IP as their default gateway. The virtual IP and virtual MAC remain available regardless of which physical router is currently active — R1 (priority 110) is active; R2 (priority 100) is standby.

11. VRRP, an open IETF standard that delivers default gateway: Which FHRP meets this requirement?

Medium
A multi-vendor network requires a first hop redundancy protocol that is vendor-neutral and supported by Cisco, Juniper, and Palo Alto routers. Which FHRP meets this requirement?
  1. HSRP, a Cisco-proprietary gateway redundancy protocol that is not interoperable with Juniper or Palo Alto devices at all
    HSRP is Cisco proprietary and is not supported in a standards-compliant way on Juniper or Palo Alto devices, so it cannot serve a multi-vendor environment.
  2. GLBP, a Cisco-proprietary protocol that adds active load balancing but runs only on Cisco IOS and IOS-XE routers
    GLBP is Cisco proprietary and, like HSRP, is not supported on non-Cisco devices, so it fails the vendor-neutral requirement despite its load-balancing feature.
  3. VRRP, an open IETF standard (RFC 5798) that delivers default gateway redundancy across Cisco, Juniper, and Palo Alto ✓
    VRRP (RFC 5798) is an IETF open standard supported across all major vendors including Cisco, Juniper, and Palo Alto. It provides the same default gateway redundancy as HSRP but in a vendor-neutral implementation.
  4. LACP, an IEEE 802.3ad protocol that negotiates EtherChannel link bundles and provides no default gateway failover
    LACP is an IEEE standard for link aggregation (EtherChannel); it is not a first hop redundancy protocol and provides no default gateway failover.
The trap
HSRP = Cisco proprietary; VRRP = open standard (IEEE RFC 5798) — multi-vendor networks require VRRP

VRRP (RFC 5798) is the vendor-neutral FHRP standard — supported by all major vendors including Cisco, Juniper, and Palo Alto. HSRP and GLBP are Cisco proprietary.

12. O means OSPF-learned: A network engineer runs 'show ip route' and sees the following entries: O 10.1.1.0/24 [1

Easy
A network engineer runs 'show ip route' and sees the following entries:
O 10.1.1.0/24 [110/2] via 192.168.1.1
C 192.168.1.0/24 is directly connected, GigabitEthernet0/0
S* 0.0.0.0/0 [1/0] via 203.0.113.1
What do the codes 'O', 'C', and 'S*' indicate respectively?
  1. O means the Optimal path chosen, C means a Cisco-specific route, and S* means a Secure default route the router trusts
    These are invented meanings. In Cisco IOS, O is OSPF, C is Connected, and S is Static, so Optimal, Cisco, and Secure are all incorrect definitions.
  2. O means OSPF-learned, C means a Configurable route entry, and S* means a Spanning tree derived forwarding path here
    C stands for Connected (a directly attached network), not Configurable, and S stands for Static, not Spanning tree, so this mapping is wrong.
  3. O means OSPF-learned, C means directly Connected, and S* means a Summary static route folding several subnets
    S* specifically flags a static route that is the gateway of last resort (default route), not a summary static route, so this option is incorrect.
  4. O means OSPF-learned, C means directly Connected, and S* means the Static default route (gateway of last resort) ✓
    Cisco routing codes: O = OSPF-learned route, C = directly connected network, S = static route; the asterisk marks S* as the gateway of last resort (default route).
The trap
S* = static default route (gateway of last resort); plain S = regular static route; L = local (the router's own interface IP as /32)

Cisco routing table codes: O = OSPF, C = Connected (directly attached), S = Static, S* = Static default route (gateway of last resort). Common codes: D=EIGRP, R=RIP, B=BGP, i=IS-IS.

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