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Zorluk: OrtaTroubleshooting Routing, Default Gateways, and ACLs

A Linux server configured with the IPv4 address 192.168.120.45/24192.168.120.45/24 is unable to establish connections with servers on external subnets. Local subnet communication functions normally. The network administrator runs `ip route show` on the server and reviews the following routing table output:

text
default via 192.168.121.1 dev eth0
192.168.120.0/24 dev eth0 proto kernel scope link src 192.168.120.45

Which of the following identifies the root cause of the connectivity failure?

  1. The default gateway IP address resides on a different IP subnet than the host's configured IP address.Cevap
  2. B
    The subnet mask on the network interface excludes valid host IP addresses in the pool.
  3. C
    The router's Access Control List is implicitly denying outbound traffic from destination port 80.
  4. D
    The network interface eth0 is assigned to an unrouted VLAN broadcast domain.

Cevap

The default gateway IP address (192.168.121.1) is configured on a different IP subnet than the server's interface IP address (192.168.120.45/24).
A default gateway must reside on the same local IP subnet as the host interface so that the host can resolve the gateway's MAC address using ARP. The host address is 192.168.120.45/24192.168.120.45/24, making the local subnet range 192.168.120.1192.168.120.1 to 192.168.120.254192.168.120.254. Because the default gateway is set to 192.168.121.1192.168.121.1, it lies outside the local subnet and cannot be reached.

Adım Adım Çözüm

1
Analyze the host's IP address configuration and subnet boundary.
The server's address is 192.168.120.45192.168.120.45 with a /24/24 prefix (255.255.255.0255.255.255.0), defining a local usable host range of 192.168.120.1192.168.120.1 through 192.168.120.254192.168.120.254.
Understanding the host's subnet boundary is required to verify gateway reachability.
2
Evaluate the default gateway IP address in the routing table output.
The default route points to `192.168.121.1`.
The gateway address 192.168.121.1192.168.121.1 resides in the 192.168.121.0/24192.168.121.0/24 network segment, which is outside the local 192.168.120.0/24192.168.120.0/24 subnet.
3
Determine the impact of the subnet mismatch on Layer 2 / Layer 3 resolution.
The host cannot resolve the MAC address of the default gateway via ARP because the gateway is not on the directly connected local subnet.
A host default gateway must always reside on the same IP subnet as the local network interface.

Anahtar Kavram

Default Gateway Subnet Alignment
Tahmini Süre:1m 30s
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Konular

Troubleshooting Routing, Default Gateways, and ACLs

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