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Difficulty: MediumIP Addressing Services

A network administrator is auditing the core infrastructure configuration for a enterprise environment with centralized network services. Centralized DHCP and DNS servers are deployed on VLAN 10 (10.10.10.0/2410.10.10.0/24), while client endpoints reside on remote VLAN 20 (10.10.20.0/2410.10.20.0/24) and utilize dual-stack IPv4/IPv6 addressing. Which TWO of the following administrative configurations or operational mechanisms are necessary to enable clients on VLAN 20 to automatically obtain valid IPv4 lease configurations and dynamically register their hostnames in name resolution services? (Select TWO.)

  1. Configuring an IP helper address (DHCP relay) on the VLAN 20 gateway interface pointing to the unicast IP address of the DHCP serverAnswer
  2. Enabling Dynamic DNS (DDNS) integration between the DHCP server and the DNS server to update A and AAAA records automatically upon lease issuanceAnswer
  3. C
    Creating PTR records on the DNS server to handle forward hostname-to-IPv6 resolution requests for remote client workstations
  4. D
    Assigning APIPA addresses on client network adapters so they can route request packets across the inter-VLAN gateway to VLAN 10
  5. E
    Opening firewall transport port 23 (Telnet) between VLAN 20 and VLAN 10 to permit lease negotiation traffic

Answer

The required mechanisms are configuring an IP helper address on the remote gateway interface to forward DHCP broadcasts across subnets, and configuring Dynamic DNS (DDNS) integration to update DNS records automatically upon lease issuance.
To allow client endpoints on VLAN 20 to receive dynamic IP address assignments from a DHCP server located on VLAN 10, the Layer 3 interface (gateway) for VLAN 20 must be configured with an IP helper address (DHCP relay agent) to convert local broadcasts into routed unicast traffic. Additionally, to ensure these dynamically addressed hosts can be resolved by name, Dynamic DNS (DDNS) must be enabled so that the DHCP server automatically registers and updates the host's A (IPv4) and AAAA (IPv6) records on the DNS server upon issuing a lease.

Step-by-Step Solution

1
Analyze the Layer 3 boundary requirement for DHCP broadcast traffic.
Identified that clients on VLAN 20 (10.10.20.0/2410.10.20.0/24) send DHCPDISCOVER as Layer 2/3 broadcasts, which routers drop by default. An IP helper address must be configured on the default gateway to relay DHCP traffic across subnets to the server on VLAN 10.
DHCP relay agents convert local broadcast requests into unicast packets routed directly to the DHCP server.
2
Analyze the requirement for dynamic hostname registration.
Identified that Dynamic DNS (DDNS) allows the DHCP server or clients to automatically notify the DNS server to create or update resource records whenever an IP lease is granted.
Without DDNS, client name resolution requires manual DNS administration for dynamic endpoints.
3
Evaluate the incorrect options based on networking protocols and service roles.
PTR records perform reverse lookups (not forward lookups), APIPA indicates DHCP discovery failure and cannot be routed, and Port 23 is Telnet rather than DHCP UDP ports 67/68.
Verifies that distractors contain fundamental protocol or misconfiguration errors.

Key Concept

IP Addressing Services (DHCP Relay and DDNS)
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Topics

IP Addressing Services

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