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Zorluk: ZorNetworking Ports and Protocols

A network administrator is configuring firewall access control lists (ACLs) between a workstation VLAN and a dedicated server VLAN hosting network services. The administrator creates a rule allowing inbound traffic on UDP port 67 from the workstation subnet to the server, but client computers are still unable to acquire dynamic IP address assignments and default to APIPA addresses (169.254.x.x169.254.x.x). Which additional firewall rule must be configured to permit successful DHCP address allocation?

  1. Permit outbound traffic on UDP port 68 from the DHCP server to the workstation subnetCevap
  2. B
    Permit outbound traffic on TCP port 67 from the DHCP server to the workstation subnet
  3. C
    Permit inbound traffic on UDP port 53 from the workstation subnet to the DHCP server
  4. D
    Permit inbound traffic on TCP port 68 from the workstation subnet to the DHCP server

Cevap

Permit outbound traffic on UDP port 68 from the DHCP server to the workstation subnet
DHCP uses a two-port UDP structure for client-server communication. DHCP servers listen for incoming client broadcast requests on UDP port 67, while clients receive server broadcast/unicast responses (DHCPOFFER and DHCPACK) on UDP port 68. Permitting outbound UDP port 68 ensures server responses can pass through the firewall back to client workstations.

Adım Adım Çözüm

1
Identify the transport protocol and port requirements for DHCP operation.
DHCP uses UDP as its transport layer protocol and relies on two specific port numbers: UDP 67 for the server listener and UDP 68 for the client listener.
Because client discovery broadcasts originate before an IP address is assigned, client and server roles listen on distinct ports.
2
Analyze the bidirectional traffic flow between client and server.
The client sends DHCP Discover and Request packets to destination UDP port 67 on the server. The server responds with DHCP Offer and Acknowledgment (ACK) packets directed to destination UDP port 68 on the client.
If the firewall permits inbound UDP 67 but blocks outbound UDP 68, client requests reach the server, but server responses are dropped before reaching workstations.
3
Determine the necessary ACL modification to complete the handshake.
Outbound traffic on UDP port 68 from the server to the client subnet must be permitted.
Allowing outbound UDP 68 completes the bidirectional path required for workstations to successfully receive IP leases.

Anahtar Kavram

DHCP Port Allocation (UDP 67 / UDP 68)
Tahmini Süre:1m 30s
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Konular

Networking Ports and Protocols

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