A network technician is troubleshooting connectivity for a VoIP desk phone on VLAN 80 (). The phone boots up and receives an IP address lease, but it cannot register with the central PBX server located on VLAN 10 (). Running a network status command on the phone reveals the following output:
text
IPv4 Address . . . . . . . . . . . : 10.80.0.45
Subnet Mask . . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . . : 10.80.1.1
DHCP Server . . . . . . . . . . . . : 10.80.0.1
DHCP Option 066 (TFTP Server) . . . : 10.10.0.10
Which of the following is the primary cause of the registration failure?
- The DHCP server configured Option 003 (Default Gateway) with an IP address on a different subnet than the host.Cevap
- BThe VoIP phone failed to receive a valid DHCP lease and automatically assigned itself an APIPA address.
- CAn IP helper address is missing on the router interface serving VLAN 80, preventing DHCP requests from reaching the server.
- DThe assigned host IP address is invalid because it represents the broadcast address for the subnet.
Cevap
The DHCP server provided a Default Gateway address (Option 003) that resides on a different subnet () than the client's assigned address (), preventing off-subnet routing.
The client received an IP address of with a subnet mask (), placing it on the subnet. The DHCP server provided Option 003 (Default Gateway) with the IP address , which belongs to the subnet. A host cannot forward packets to a default gateway that does not reside on its local IP subnet, which prevents the VoIP phone from routing traffic to the PBX server on VLAN 10.
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DHCP Option 003 Default Gateway Subnet Mismatch Troubleshooting