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Difficulty: MediumTroubleshooting IP Addressing and DHCP Services

A network administrator is troubleshooting an issue where newly deployed host systems on a corporate subnet (10.100.40.0/2410.100.40.0/24) can communicate with local peers but fail to reach external subnets or internet services. Executing `ipconfig /all` on one of the affected hosts produces the following output:

text
IPv4 Address. . . . . . . . . . . : 10.100.40.88
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.100.4.1
DHCP Server . . . . . . . . . . . : 10.100.1.10

Which of the following options accurately identify the root cause of this connectivity failure and the appropriate corrective action? (Select TWO.)

  1. The assigned default gateway address (10.100.4.1) resides on a different IP subnet than the host's IPv4 address (10.100.40.88/24).Answer
  2. Reconfigure DHCP Scope Option 003 on the server to distribute a default gateway IP within the local 10.100.40.0/24 subnet.Answer
  3. C
    The client system failed to locate a active DHCP server and generated an Automatic Private IP Addressing (APIPA) address.
  4. D
    Configure an IP Helper address on the host switchport to forward local ARP request broadcasts directly to the gateway router.

Answer

The host cannot reach remote networks because its default gateway (10.100.4.1) is on a different subnet than its assigned IP address (10.100.40.88/24). Reconfiguring DHCP Scope Option 003 on the DHCP server to distribute a gateway address on the 10.100.40.0/24 subnet resolves the issue.
The client host is assigned an IP address of 10.100.40.88 with a /24 subnet mask (255.255.255.0), placing it in the 10.100.40.0/24 network segment. The configured default gateway is 10.100.4.1, which resides on a completely different IP subnet (10.100.4.0/24). A host cannot route off-subnet traffic if its default gateway does not share its local subnet prefix. Because the configuration was provided dynamically, updating DHCP Option 003 on the DHCP server to supply a gateway address within 10.100.40.0/24 resolves the issue for all affected clients.

Step-by-Step Solution

1
Analyze client IP configuration and subnet boundaries.
Host IP is 10.100.40.88 with subnet mask 255.255.255.0 (/24). The usable host IP range for this subnet is 10.100.40.1 through 10.100.40.254.
To send packets outside the local broadcast domain, a host must forward traffic to a gateway located within its local network prefix.
2
Compare default gateway address to host subnet.
The configured default gateway address is 10.100.4.1, which falls outside the 10.100.40.0/24 subnet prefix (it belongs to 10.100.4.0/24).
Because the gateway is not on the same broadcast domain, ARP resolution fails and remote packets cannot be forwarded.
3
Determine root source of misconfiguration and appropriate remedy.
The client received this configuration from DHCP Server 10.100.1.10. Reconfiguring DHCP Scope Option 003 (Router) for the 10.100.40.0/24 scope ensures clients automatically receive a gateway address within 10.100.40.0/24.
DHCP Option 003 dictates the default gateway IP address assigned to dynamic DHCP clients.

Key Concept

Default Gateway Subnet Alignment and DHCP Scope Option 003 Configuration
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Topics

Troubleshooting IP Addressing and DHCP Services

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