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300-410 Practice Question: A large enterprise network is experiencing…

A large enterprise network is experiencing intermittent reachability to a specific /24 subnet (192.168.10.0/24) from remote sites. Router R1 has the following relevant configuration:

interface GigabitEthernet0/0
 ip address 10.0.1.1 255.255.255.0

!

router eigrp 100
 network 10.0.0.0
 network 192.168.0.0

!

interface GigabitEthernet0/1
 ip address 192.168.1.1 255.255.255.0
 ip summary-address eigrp 100 192.168.0.0 255.255.252.0

!

Router R2 shows:
R2# show ip route 192.168.10.0

Routing entry for 192.168.0.0/22, supernet Known via "eigrp 100", distance 90, metric 30720, type internal Last update from 10.0.1.1 on GigabitEthernet0/0, 00:00:15 ago

* 10.0.1.1, via GigabitEthernet0/0, 00:00:15 ago

What is the root cause?

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

The summary route 192.168.0.0/22 does not include 192.168.10.0/24, so the specific route is not advertised and is missing from R2's routing table.

The summary route 192.168.0.0/22 is being advertised by R1, but it blocks the more specific /24 route 192.168.10.0/24 if that subnet is not within the summary range (192.168.0.0/22 covers 192.168.0.0 to 192.168.3.255). Since 192.168.10.0/24 is outside this range, it is not summarized and is not advertised separately, causing reachability failure. The correct fix is to adjust the summary prefix to include the missing subnet, or to not summarize.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • The summary route 192.168.0.0/22 does not include 192.168.10.0/24, so the specific route is not advertised and is missing from R2's routing table.

    Why this is correct

    The summary covers only 192.168.0.0-192.168.3.255, excluding 192.168.10.0/24.

  • EIGRP has a metric mismatch between the summary and the specific route, causing the specific route to be suppressed.

    Why it's wrong here

    EIGRP does not suppress specific routes due to metric mismatch; the summary is simply not covering the subnet.

  • The network command for 192.168.0.0 is missing, causing EIGRP to not advertise any 192.168.x.x routes.

    Why it's wrong here

    The network command includes 192.168.0.0, so routes are advertised.

  • R2 has a static route for 192.168.10.0/24 that is overriding the EIGRP route.

    Why it's wrong here

    No static route is shown; the issue is with the summary.

Visual reference

192.168.1.0 /24 256 addresses (254 usable) 192.168.1.0 /25 Subnet A 128 addr (126 usable) 192.168.1.128 /25 Subnet B 128 addr (126 usable) Borrowing 1 bit from host portion creates 2 subnets (/25)

Quick reference

Routing Protocol Comparison

ProtocolMetricMax HopsAlgorithmType
RIP v2Hop count15Bellman-FordDistance vector
OSPFCost (bandwidth)UnlimitedDijkstra (SPF)Link state
EIGRPComposite metricUnlimitedDUALHybrid
IS-ISCostUnlimitedDijkstraLink state
BGPPolicy / attributesUnlimitedPath vectorPath vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

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Last reviewed: Jun 18, 2026

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