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Zorluk: OrtaDHCP Server, Client, and Relay Agent Operation and Configuration

A host client on a remote subnetwork requires an IPv4 address assignment from a centralized server. Place the operational steps in the correct sequential order to illustrate how a Cisco router configured with `ip helper-address` processes and relays the initial discovery and offer messages.

  1. 1The host client broadcasts a DHCPDISCOVER packet with source IP 0.0.0.00.0.0.0 and destination IP 255.255.255.255255.255.255.255 on its local subnet.
  2. 2The router receives the broadcast, inserts its ingress interface IP address into the giaddr field, and unicasts the DHCPDISCOVER packet to the configured helper address.
  3. 3The central DHCP server evaluates the giaddr field to match the correct address pool and returns a unicast DHCPOFFER packet to the router giaddr.
  4. 4The router receives the unicast DHCPOFFER packet on its server-facing interface and forwards it onto the client-facing subnet toward the requesting host.

Cevap

The correct operational sequence begins with the client broadcasting a DHCPDISCOVER packet on the local subnet. Next, the relay agent router intercepts the broadcast, inserts its ingress interface IP into the giaddr field, and forwards the packet as a unicast transmission to the DHCP server. The central DHCP server then matches the giaddr to its address pool and returns a unicast DHCPOFFER to the router's giaddr address. Finally, the router receives the DHCPOFFER and forwards it onto the local subnet to the host client.
The workflow follows standard DHCP relay behavior: (1) Host sends broadcast DHCPDISCOVER, (2) Relay agent populates the giaddr field with its interface IP and unicasts the request to the central server, (3) Server evaluates giaddr to select the subnet pool and unicasts DHCPOFFER back to giaddr, and (4) Relay agent forwards the offer to the local client.

Adım Adım Çözüm

1
Identify host initialization
Host generates a local Layer 3 broadcast DHCPDISCOVER (0.0.0.0255.255.255.2550.0.0.0 \rightarrow 255.255.255.255).
Clients without IP addresses must broadcast locally to locate an active DHCP server.
2
Identify relay agent header modification and forwarding
Router populates giaddr with its subinterface IP and unicasts the packet to the server address specified by the ip helper-address command.
Routers drop Layer 3 broadcasts by default; the helper address command enables broadcast-to-unicast conversion and inserts gateway context.
3
Identify server pool matching and reply
DHCP server matches the giaddr to the appropriate IP scope and sends a unicast DHCPOFFER back to the relay agent IP.
The central server uses the giaddr field to identify which remote subnet requires an IP lease.
4
Identify relay delivery to the client
Router receives the DHCPOFFER and delivers it to the target client on the local subnet.
The relay agent completes the forward relay process by sending the offer down to the originating host.

Anahtar Kavram

DHCP Relay Agent Operational Processing Sequence
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