Quick Answer
The answer is the nfs service must be added to the firewall. This is correct because on RHEL 8, the firewalld service uses predefined service definitions to open specific ports, and the nfs service opens TCP and UDP port 2049, which is the standard port for NFSv4 traffic. Even when NFS-related services like rpcbind or nfs-server are enabled and running, and exportfs -v confirms the share is exported, the firewall still needs an explicit rule to permit incoming connections on port 2049; without it, clients attempting an NFS mount will be blocked. On the CompTIA Linux+ XK0-005 exam, this question tests your understanding that enabling a service does not automatically open its firewall port—a common trap where candidates assume "NFS-related services are enabled" means the firewall is already configured. A helpful memory tip is to remember that NFS needs its own firewall rule because it uses a dedicated port (2049), unlike older NFS versions that relied on rpcbind port mapping.
This XK0-005 practice question tests your understanding of troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A file server running RHEL 8 uses NFS to export directories. Clients report that they cannot mount an NFS share. The server's firewall is configured but NFS-related services are enabled. The administrator checks `exportfs -v` and sees the export is listed. Which service must be added to the firewall to allow NFS?
rpc-bind
Why wrong: rpc-bind is needed for RPC, but enabling nfs service typically covers it.
nfs
The nfs service is essential; adding it allows the NFS server port (2049).
samba
Why wrong: Samba is for SMB/CIFS, not NFS.
mountd
Why wrong: mountd is required for NFS mounts but is not the core service; it is often part of the nfs service group.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
nfs
Option B is correct because NFS on RHEL 8 requires the 'nfs' service to be added to the firewall to allow incoming NFS traffic. The 'nfs' service in firewalld opens TCP and UDP ports 2049, which is the standard port for NFSv4. Even though NFS-related services are enabled, the firewall must explicitly permit this port for clients to mount the share.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
rpc-bind
Why it's wrong here
rpc-bind is needed for RPC, but enabling nfs service typically covers it.
nfs
Why this is correct
The nfs service is essential; adding it allows the NFS server port (2049).
Related concept
Read the scenario before looking for a memorised answer.
samba
Why it's wrong here
Samba is for SMB/CIFS, not NFS.
mountd
Why it's wrong here
mountd is required for NFS mounts but is not the core service; it is often part of the nfs service group.
Common exam traps
CompTIA often tests the misconception that 'mountd' is a valid firewalld service name, when in fact it must be configured as a custom port or covered by the 'nfs' service, leading candidates to select option D incorrectly.
Detailed technical explanation
NFSv4 uses a single TCP port 2049, simplifying firewall rules compared to NFSv3 which requires multiple RPC services (portmapper, mountd, nlockmgr, etc.) with dynamic ports. In RHEL 8, the 'nfs' service in firewalld covers both TCP and UDP on port 2049, and if NFSv3 is needed, additional services like 'rpc-bind' and 'mountd' (with static ports configured in /etc/sysconfig/nfs) must be added. A real-world scenario is a mixed NFSv3/v4 environment where forgetting to add 'rpc-bind' causes mounts to fail for legacy clients.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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FAQ
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
The correct answer is: nfs — Option B is correct because NFS on RHEL 8 requires the 'nfs' service to be added to the firewall to allow incoming NFS traffic. The 'nfs' service in firewalld opens TCP and UDP ports 2049, which is the standard port for NFSv4. Even though NFS-related services are enabled, the firewall must explicitly permit this port for clients to mount the share.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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