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Zorluk: OrtaDHCP Architecture and Relay Services

A client host on a newly configured workstation network (VLAN 30) initiates an IP address lease request. A Layer 3 switch configured with an IP helper address relays this request to a centralized DHCP server located on a separate management network. Place the sequence of events handling the DHCPDISCOVER and DHCPOFFER exchange in chronological order from initial client transmission to final relay delivery.

  1. 1The client host broadcasts a DHCPDISCOVER packet onto local VLAN 30 using source port UDP 68 and destination port UDP 67.
  2. 2The Layer 3 switch interface receives the broadcast, inserts its local SVI IPv4 address into the giaddr header field, and encapsulates the request into a unicast packet sent to the remote DHCP server.
  3. 3The remote DHCP server receives the unicast packet, inspects the giaddr header field, and selects an available IP address from the matching VLAN 30 scope.
  4. 4The DHCP server generates a DHCPOFFER packet and unicasts it back to the relay agent's SVI address on UDP port 67.
  5. 5The Layer 3 switch receives the unicast DHCPOFFER on its SVI and forwards the offer packet onto VLAN 30 targeted to the client on UDP port 68.

Cevap

The chronological sequence of the relayed DHCP exchange is: 1) Client broadcasts DHCPDISCOVER on local VLAN 30; 2) Relay agent populates giaddr and unicasts request to DHCP server; 3) DHCP server selects address pool matching giaddr; 4) DHCP server unicasts DHCPOFFER to relay agent SVI IP; 5) Relay agent forwards DHCPOFFER to client on VLAN 30.
The correct sequence follows the standard DHCP relay process: first, the client host broadcasts a DHCPDISCOVER message locally on UDP port 67. The Layer 3 relay agent intercepts this broadcast, inserts its SVI address into the giaddr header field, and forwards the packet via unicast to the DHCP server. The DHCP server uses the giaddr value to choose the correct subnet pool and returns a unicast DHCPOFFER to the relay agent on UDP port 67. Finally, the relay agent forwards the DHCPOFFER to the client host on UDP port 68.

Adım Adım Çözüm

1
Identify initial local broadcast
The unconfigured host transmits a broadcast DHCPDISCOVER frame on UDP port 67 across VLAN 30.
Hosts lacking IP addresses must initiate communications using local Layer 2 and Layer 3 broadcasts.
2
Trace relay agent header modification and forwarding
The Layer 3 switch SVI captures the broadcast, populates the giaddr header field with its interface IP, and forwards a unicast packet to the server on UDP port 67.
The relay agent converts non-routable local broadcasts into routable unicast traffic while adding subnet tracking information.
3
Determine server address allocation logic
The DHCP server matches the giaddr field to its configured address scope for VLAN 30 and reserves an available lease.
The giaddr field explicitly informs the centralized server which subnet pool must be used for assignment.
4
Trace server response transmission
The DHCP server creates a DHCPOFFER and sends it as a unicast packet directly to the relay agent's giaddr on UDP port 67.
The server returns the payload to the relay agent because the client cannot be reached across routed networks directly.
5
Verify final delivery to client
The relay agent receives the offer and sends a DHCPOFFER packet onto VLAN 30 addressed to the client on UDP port 68.
The relay agent delivers the leased address details back to the host on its local access segment.

Anahtar Kavram

DHCP Relay Packet Processing and Header Modification Lifecycle
Tahmini Süre:1m 30s
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DHCP Architecture and Relay Services

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