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Question

Difficulty: EasyTroubleshooting Routing, Default Gateways, and ACLs

A network technician is troubleshooting a workstation that cannot communicate with servers on remote subnets. The technician executes `ipconfig` on the workstation and observes the following network settings:

text
IPv4 Address. . . . . . . . . . . : 192.168.1.50
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.2.1

The workstation can ping local host 192.168.1.10192.168.1.10, but all outbound traffic to external networks fails. Which of the following is the root cause of the connectivity failure?

  1. The default gateway is configured on a different IP subnet than the host.Answer
  2. B
    The host has assigned itself an APIPA address because DHCP leasing failed.
  3. C
    The default gateway IP address is unusable because it is a network broadcast address.
  4. D
    The host and default gateway cannot communicate due to a missing VLAN tagging protocol on the network adapter.

Answer

The default gateway is configured on a different IP subnet than the host.
For a host device to send traffic outside its local network, its configured default gateway must be an IP address located on the same IP subnet. The host is configured with 192.168.1.50/24192.168.1.50/24, but the gateway is set to 192.168.2.1/24192.168.2.1/24. Because they reside on different subnets, the host cannot ARP for the gateway's MAC address, preventing all traffic destined for remote networks.

Step-by-Step Solution

1
Analyze host IP address and subnet mask.
IP address 192.168.1.50192.168.1.50 with subnet mask 255.255.255.0255.255.255.0 (/24) places the host in the local network range 192.168.1.1192.168.1.1 through 192.168.1.254192.168.1.254.
Determines the valid local subnet boundary.
2
Compare the default gateway address to the host's subnet range.
The configured default gateway 192.168.2.1192.168.2.1 falls into the 192.168.2.0/24192.168.2.0/24 subnet.
Identifies whether the gateway is directly reachable via local Layer 2 broadcast domain.
3
Determine why outbound communication fails.
Because the default gateway is not on the same IP subnet, the host cannot perform ARP resolution to forward off-subnet traffic to its gateway router.
Confirms the root cause of failure for remote destination traffic.

Key Concept

Default Gateway Subnet Matching
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Topics

Troubleshooting Routing, Default Gateways, and ACLs

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