A network administrator installs a new set of IP phones on a dedicated voice VLAN (VLAN 40). The enterprise DHCP server resides on VLAN 10. The phones fail to obtain IP addresses and automatically configure APIPA addresses instead. Which TWO of the following resolution actions or diagnostic steps should the technician perform to troubleshoot and resolve this issue? (Select TWO)
- Configure an IP helper address (DHCP relay agent) pointing to the DHCP server IP on the VLAN 40 router interface.Cevap
- Verify that intermediate firewalls and access control lists (ACLs) permit UDP ports 67 and 68 traffic between VLAN 40 and VLAN 10.Cevap
- CAssign static APIPA addresses (169.254.x.x) to the phones so they can route traffic through the default gateway.
- DChange the DHCP scope subnet mask from /24 to /25 to double the number of available usable host IP addresses.
Cevap
The technician should configure an IP helper address (DHCP relay agent) on the VLAN 40 gateway interface and verify that intermediate ACLs permit traffic on UDP ports 67 and 68.
DHCP client requests rely on Layer 2 broadcasts that default gateway routers do not forward. Configuring an IP helper address (DHCP relay) on the interface facing the client subnet enables the router to encapsulate DISCOVER broadcasts into unicast packets directed to the central DHCP server. Additionally, verifying that security controls permit traffic on UDP ports 67 and 68 ensures that relayed DHCP traffic passes through intermediate interfaces without being dropped.
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Troubleshooting Cross-Subnet DHCP Relay and Port Accessibility