Free 300-625 Practice Test Questions and Answers (2026)

The FCoE Initialization Protocol (FIP) is the control plane protocol for Fibre Channel over Ethernet (FCoE). It is responsible for discovering FCoE-capable entities, establishing virtual links, and performing fabric login. To differentiate these critical control plane frames from the actual FCoE data plane traffic and other Ethernet protocols, the IEEE assigned FIP the unique EtherType of 0x8914. This allows FCoE-aware switches (FCoE Forwarders) to intercept and process discovery and login requests before the data-carrying virtual link is established.

A. 0x8913: This EtherType is unassigned by the IEEE and is not used for FCoE or FIP.
C. 0xfc0e: This is not a valid or standardized EtherType and is likely included as a distractor due to the "FC" characters.
D. 0x8906: This is the correct EtherType for FCoE data frames, which encapsulate Fibre Channel payloads, not for the FIP control frames.

1. INCITS 462-2010 (T11/09-243v3), Information technology - Fibre Channel - Backbone - 5 (FC-BB-5), Section 5.2, "FCoE and FIP EtherTypes", Page 23. This standard, which defines FCoE, explicitly states: "The FCoE Initialization Protocol (FIP) shall use the EtherType value 8914h."

2. Cisco, Cisco MDS 9000 Series NX-OS Fundamentals Guide, Release 8.x, "FCoE and DCB," Section: "FCoE Initialization Protocol." The documentation describes FIP as the mechanism for an ENode to discover and log in to an FCF, operating on a distinct EtherType from FCoE.

3. Cisco, Cisco Nexus 9000 Series NX-OS SAN Switching Configuration Guide, Release 10.3(x), Chapter: "Configuring FCoE," Section: "Information About FCoE." This guide details the FCoE architecture, noting that FIP (EtherType 0x8914) handles control plane functions like discovery and login, while FCoE (EtherType 0x8906) handles the data plane.

The principal switch in a Fibre Channel fabric is responsible for managing and assigning unique domain IDs to all other switches. When a subordinate switch requests a specific domain ID, the assignment can fail for two primary reasons. First, if the requested domain ID is already allocated to another switch in the fabric, the principal switch will reject the request to prevent a conflict, as all domain IDs must be unique. Second, administrators can configure an "allowed domain ID list" on a per-VSAN basis. If the subordinate switch requests a domain ID that is not part of this pre-approved list, the principal switch will deny the request to enforce fabric policy and maintain a deterministic topology.

A. Cisco Fabric Services (CFS) is for distributing configuration information like zoning, not for the fundamental protocol of switch domain ID assignment.
B. While a fabric lock would prevent domain assignment, domain conflicts and policy violations are more direct causes related to the specific value of the requested ID.
D. The persistent FC ID feature ensures end devices (N-Ports) retain their Fibre Channel IDs, which is unrelated to the switch-level domain ID assignment process.

1. Cisco MDS 9000 Series NX-OS Fabric Configuration Guide, Release 8.x, Chapter: "Configuring fcdomain", Section: "About Domain ID Assignment". This section states, "If the requested domain ID is not available, or if it is not in the allowed list, the principal switch assigns a different domain ID." This directly supports that a conflict (not available) or not being on the allowed list are reasons for failure to obtain the requested ID.

2. Cisco MDS 9000 Series NX-OS Fundamentals Configuration Guide, Release 8.x, Chapter: "Fabric and VSAN Management", Section: "Domain Parameters". This guide explains the uniqueness requirement for domain IDs within a fabric: "Each switch in a fabric is uniquely identified by its domain ID." This underpins why a request for an already-assigned ID (Option E) must be rejected.

3. Cisco Nexus 5600 Series NX-OS FabricPath Configuration Guide, Release 7.x, Chapter: "Configuring FCoE", Section: "Configuring fcdomain Features". While for a different platform, the underlying NX-OS fcdomain principles are the same. It describes the fcdomain allowed command, which "Configures the list of allowed domain IDs for a VSAN," confirming the policy mechanism mentioned in Option C.

When two Cisco MDS fabrics with Inter-VSAN Routing (IVR) enabled are merged, the resulting configuration is determined by a set of merge rules. For the service groups (which are part of the IVR zone set), the resulting merged fabric will only contain the service groups that are common to both fabrics. This is known as the intersection of the two configurations. In the provided exhibit, the local fabric has Group1 and Group2, while the peer fabric only has Group1. The intersection of these two sets is Group1. Therefore, the Merged Fabric Information correctly shows that the resulting fabric will only contain Group1.

A. The merged fabric IVR VSAN topology is set to activate. This is a precondition for a successful merge, not a result of it. Both fabrics must have an active IVR topology for the merge to proceed.
B. The merged fabric has NAT enabled. This is also a precondition for a successful merge. Both fabrics must have the same NAT setting (either enabled or disabled) for the merge to be valid.
C. The merge is invalid. The merge is valid and in progress. The differing service group configurations do not invalidate the merge; they are resolved by taking the intersection of the groups.

1. Cisco MDS 9000 Series NX-OS SAN Switching Configuration Guide, Release 9.3(x)

Section: Configuring IVR > Merging IVR Fabrics

Content: "When two fabrics with IVR merge, the IVR zone sets are also merged. The merged IVR zone set is the intersection of the IVR zone sets in the two fabrics." This document also lists the compatibility requirements for a merge, stating that IVR NAT must be consistently enabled or disabled, and the IVR VSAN topology must be active on both fabrics. This supports why options A, B, and C are incorrect.

2. Cisco MDS 9000 Series NX-OS Fundamentals Guide, Release 8.x

Section: Fabric Configuration > Merging Fabrics

Content: This guide explains the general principles of fabric merges, including the requirement for compatible parameters. In the context of IVR, "If the IVR configurations are compatible, the fabrics merge successfully... The IVR configuration is then merged. The merged IVR zone set is the intersection of the IVR zone sets in the two fabrics." This directly supports the logic for answer D.

When an NPV device brings up an NP port, it executes an internal FLOGI process to log into the core NPIV switch. Cisco documentation explicitly maps these FLOGI parameters to their sources:

1. pWWN: Derived from the fWWN (Factory WWN) of the NP port (the physical port on the NPV device).
2. nWWN: Derived from the VSAN-based sWWN (Switch WWN) of the NPV device itself.
3. fWWN: Associated with the fWWN of the F Port on the NPV core switch (identifying the upstream fabric port).
4. Symbolic node name: Derived from the NPV switch name.
5. IP address: Derived from the IP address of the NPV device (used for management/registration).

Cisco MDS 9000 Family NX-OS Interfaces Configuration Guide. Chapter: Configuring N Port Virtualization. Section: NPV Guidelines - Internal FLOGI Parameters.

Reference: "The following table identifies the parameters used in this internal FLOGI and the sources from which they are derived... pWWN: The fWWN of the NP port... nWWN: The VSAN-based sWWN of the NPV device... fWWN: The fWWN of the F port on the NPV core switch."

Cisco Nexus 5000 Series NX-OS SAN Switching Configuration Guide, Release 5.0(3)N1(1). Chapter: Configuring N Port Virtualization. Section: Internal FLOGI Parameters.

Reference: Contains the identical table mapping pWWN, nWWN, fWWN, symbolic node name, and IP address to the specific derivations listed in the answer.

The exhibit displays a "Merge Error: Full and active zoneset databases are not compatible," which indicates a zoning database merge failure within VSAN 100. This type of failure occurs when fundamental zoning parameters are inconsistent between switches in the same fabric. The default zone policy, which dictates whether traffic between non-zoned devices is permitted or denied, is a critical fabric-wide parameter that must be consistent. The default setting is deny. If another engineer changed this policy to permit on a different switch, its zoning database becomes fundamentally incompatible with switches using the deny policy. When the engineer on MDS-A activated a zoneset (which operates under the implicit deny policy), the merge with the conflicting switch failed, segmenting the fabric and causing the outage.

A. Activating another zoneset on the same switch (MDS-A) would simply replace the active one; it would not cause a merge conflict with another switch.
B. While a zone mode mismatch (basic vs. enhanced) also causes a merge failure, a default policy change is an equally fundamental and valid cause for this specific error.
C. Activating a different zoneset on another switch also causes a merge failure, but the "not compatible" error often points to a more structural incompatibility like policy.

1. Cisco MDS 9000 Series NX-OS Fundamentals Configuration Guide, Release 8.x, Chapter: Configuring and Managing Zones, Section: Default Zone.

This document states, "The default zone policy (permit or deny) must be configured consistently on all switches in the fabric. An inconsistency in the default zone policy setting between switches can cause a merge failure, which results in the fabric being segmented." This directly links the action in option D to the observed problem.

2. Cisco MDS 9000 Series NX-OS Fundamentals Configuration Guide, Release 8.x, Chapter: Configuring and Managing Zones, Section: Zoning Database Merge.

This section details the causes of merge failures, explicitly listing "Different default zone policies" as a primary reason. It explains that the entire fabric within a VSAN must agree on these fundamental parameters for a merge to succeed.

3. Implementing Cisco Storage Networking Solutions (DCSAN) 300-625, Official Cert Guide, Chapter 5: Zoning, Section: Zoning Database Distribution and Merging.

This official guide lists "Incompatible default zone policies (permit versus deny)" as one of the key reasons for a zoning merge failure, reinforcing that the scenario described in option D is a valid and tested cause for the observed error and outage.

During the “setup” dialogue that runs the first time a Cisco MDS 9000-series switch boots, the wizard obliges the user to enter a password that satisfies the NX-OS strong-password rules, thereby enforcing the secure-password standard (option B). The same dialogue also asks, for every VSAN, whether the default-zone policy should permit or deny traffic; therefore the engineer can configure the default zone policy at this stage (option C).

A. The built-in account name “admin” is immutable; you may only set its password or add other users.
D. Port trunk mode parameters are interface-level settings and are not offered by the initial setup wizard.
E. The wizard explicitly prompts: “Enable full zoneset distribution (yes/no)”; hence the engineer does have that choice.

1. Cisco MDS 9000 Series NX-OS Fundamentals Configuration Guide, Release 9.3(x), “Running the Setup Utility”, step list: prompts for default-zone policy and “Enable full zoneset distribution (yes/no)”, pp. 2-5.

2. Cisco MDS 9000 Series Security Configuration Guide, Release 9.3(x), “Password Strength and Complexity Requirements”, Table 2-1, p. 2-3 (wizard enforces rules during initial setup).

3. Cisco MDS 9000 Series NX-OS Security Configuration Guide, Release 9.2(x), “Default User Accounts”, section “admin Account Cannot Be Deleted or Renamed”, p. 1-6.

The command output shows No-drop-cos: 3, which designates Class of Service (CoS) 3 for lossless transport using Priority Flow Control (PFC). The Data Center Bridging Exchange (DCBX) protocol is used to advertise and negotiate data center bridging capabilities between two connected peers. A critical part of this negotiation is communicating which CoS values are configured for no-drop service. Therefore, the switch advertises that CoS 3 is a no-drop class to its peer via DCBX to ensure consistent end-to-end lossless behavior for that traffic.

B. LFC is prioritized over PFC on Ethernet 1/10. This is incorrect. The output shows PFC operational-status: on and LLC-FC operational-status: off. This indicates PFC is the active flow control mechanism, demonstrating its priority over Link-Level Flow Control (LFC).
C. PFC operates on Ethernet 1/10 regardless of the capability of the peer. This is incorrect. The PFC administrative-mode: auto setting means the switch negotiates PFC capability with the peer using DCBX. PFC only becomes operational if the peer also supports and agrees to use it.
D. PFC fails to operate properly unless LFC is disabled on Ethernet 1/10. This is incorrect. The output shows PFC is operational (PFC operational-status: on) while LFC is still administratively enabled (LLC-FC administrative-mode: on). PFC and LFC are operationally mutually exclusive, but one does not need to be administratively disabled for the other to function.

1. Cisco Nexus 9000 Series NX-OS Quality of Service Configuration Guide, Release 10.2(x)

Section: Configuring Priority Flow Control > PFC Overview

Content: "The switch uses DCBX to exchange the PFC configuration with the peer. DCBX is enabled by default. PFC is a hop-by-hop flow control mechanism. The switch can receive PFC frames from a connected peer, and it can transmit PFC frames to the peer." This confirms DCBX is used to exchange PFC configuration, which includes no-drop CoS values.

2. Cisco Nexus 7000 Series NX-OS Quality of Service Configuration Guide

Section: Configuring Priority Flow Control > PFC Negotiation

Content: "When you enable PFC in auto mode, the PFC feature is enabled on an interface only if the peer device also supports PFC. The switch advertises its PFC capability to the peer device using the DCB Exchange Protocol (DCBX)." This supports the reasoning for why option C is incorrect and reinforces that PFC capabilities are advertised via DCBX.

3. Cisco Nexus 5600 Series NX-OS Quality of Service Configuration Guide, Release 7.x

Section: Configuring Priority Flow Control > PFC and Link-Level Flow Control Interaction

Content: "PFC and link-level flow control are mutually exclusive. You can enable both features on a switch, but you can enable them on an interface in different modes. Only one of them can be active on an interface at any time." This explains the relationship between PFC and LFC, showing why option D is incorrect.

When a domain ID conflict occurs, the fabric is already segmented, and traffic across the conflicting switches is disrupted. After configuring a new, unique static domain ID, the change must be applied. An fcdomain disruptive restart is the most direct and fastest method to force the switch to adopt the new configuration. This command immediately brings down the Inter-Switch Links (ISLs), forces a fabric reconfiguration, and allows the switch to join the fabric with its new, non-conflicting domain ID. This clean-slate approach ensures the quickest resolution in an already unstable fabric state.

B. Issue an fcdomain nondisruptive restart. A non-disruptive restart is intended for planned changes in a stable fabric and may fail or take longer to converge in a conflict-induced unstable state.
C. Enter the commands for a VSAN suspend / no-suspend. Suspending and re-enabling an entire VSAN is a far more impactful and time-consuming operation than restarting a single process, making it inefficient for this specific issue.
D. Enter the commands to complete a domain manager fast restart. This is not a standard, documented Cisco MDS command. The correct command syntax for restarting the domain manager process is fcdomain restart.

1. Cisco MDS 9000 Series Fabric Configuration Guide, NX-OS Release 8.x, "Configuring Domain Parameters" section.

Reference: In the subsection "Restarting the Domain Merge Process," the guide describes the fcdomain restart command. It explains that a disruptive restart forces the local switch to reacquire a domain ID, which is necessary to apply a new static ID in a conflict scenario. The disruptive nature is acceptable as the fabric is already segmented.

2. Cisco MDS 9000 Series Command Reference, NX-OS Release 8.x, fcdomain restart command description.

Reference: The documentation for the fcdomain restart disruptive command specifies that it forces a reconfiguration of the fabric by taking the E ports offline and then bringing them back online. This forced re-initialization is the most expedient way to resolve a domain ID conflict after correcting the configuration.

3. Cisco MDS 9000 Series Troubleshooting Guide, "Troubleshooting Fibre Channel Domain and Fabric Merge Issues" chapter.

Reference: This guide details the steps for resolving domain ID conflicts. The procedure involves identifying the conflict, assigning a unique static domain ID to one of the switches, and then executing an fcdomain restart disruptive on that switch to force it to rejoin the fabric with the new ID.

The primary benefit of the Cisco Data Center Network Manager (DCNM) server-based advanced feature license is its portability. Unlike traditional node-locked licenses tied to a specific switch's serial number, the server-based license is managed by the DCNM server. This decouples the license from the physical hardware, allowing the license to be easily unassigned from an old or failed switch and reassigned to a new replacement switch within the same product family (e.g., another MDS 9000 series switch). This protects the license investment during hardware refresh cycles or RMA procedures.

B. The server-based license is tied to the DCNM server's host ID (derived from its MAC address), not the switch serial number. The option's "either/or" claim is incorrect.
C. The DCNM advanced license is counted per-chassis for the number of devices being managed. It is not an unlimited device license.
D. Licenses are specific to a product family. An MDS license cannot be reassigned to a different product line, such as a Cisco Nexus switch.

1. Cisco DCNM Licensing Guide, Release 11.5(1), "DCNM-SAN-ADVANTAGE License" section.

Reference for Correct Answer (A): "The DCNM server-based licenses are not tied to the switch hardware. This allows you to reassign a license when you replace a switch with a newer version of the switch."

Reference for Incorrect Option (B): "The DCNM server license file is generated by Cisco based on the DCNM server host ID." This confirms the license is tied to the server, not the switch.

Reference for Incorrect Option (C): "The DCNM-SAN-ADVANTAGE license is a per-switch chassis license." This contradicts the claim of an unlimited number of devices.

Reference for Incorrect Option (D): The guide specifies licenses for different platforms (e.g., DCNM-SAN-ADVANTAGE for MDS). There is no mention of cross-platform re-assignment between MDS and Nexus as a standard feature.

The system logs on MDS-A clearly indicate a zone merge failure (%ZONE-2-ZSMERGEFAILED) on VSAN 10 over interface fc1/11. The reason is a "Zone name mismatch," and the subsequent log (%ZONE-3-ZONEADDFAILED) specifies that pWWN 11:11:11:11:11:11:11:13 could not be added to zone Server11. This implies MDS-A's configuration for zone Server11 is incomplete compared to MDS-B's. The correct resolution involves two steps:
1. Correct the configuration mismatch by adding the missing pWWN to the Server11 zone on MDS-A and activating the updated zoneset.
2. Re-initialize the ISL to trigger a new merge attempt. The standard, documented procedure to recover an interface from this error-disabled state (%PORT-5-IFDOWNISLCFGMISMATCH) is to perform a shutdown and no shutdown on the physical interface.

B: Deactivating the zoneset is excessively service-impacting. It removes all active zoning rules, likely causing a widespread outage for devices in VSAN 10 by enforcing the default deny policy. C: While fixing the zone is correct, removing and re-adding the VSAN from the trunk's allowed list is not the standard recommended recovery procedure for this specific error state, which is a shut/no shut. D: This action would propagate the incorrect (incomplete) zone database from MDS-A to MDS-B, as the logs on MDS-A indicate it has the missing member.

1. Cisco, Cisco MDS 9000 Series Troubleshooting Guide, "Troubleshooting Zoning" chapter, "Troubleshooting Zone Merge Failure" section. This guide explicitly states the recovery procedure: "After you have resolved the cause of the failure, you must shut down and then re-enable the interface on which the failure occurred." This directly supports the shut/no shut action in option A.

2. Cisco, Cisco MDS 9000 Series Fabric Configuration Guide, Release 8.x, "Configuring and Managing Zones" chapter, "About Zone Merges" section. This document explains that when a zone merge fails, "the E port is isolated for that VSAN." To resolve this, the configuration mismatch must be corrected, and the link must be re-initialized.

3. Cisco, Cisco MDS 9000 Series System Messages Guide, Message ID %ZONE-2-ZSMERGEFAILED. The recommended action for this message is: "Check the reason for the merge failure. If the reason is a configuration mismatch, correct the configuration on one of the switches and re-enable the port." This confirms the two-step process of fixing the configuration and then re-enabling the port.

Cisco Secure Boot establishes a "Chain of Trust" that ensures the device runs only genuine, signed software. The sequence begins with a hardware anchor (such as the Trust Anchor module or TAm), which stores the immutable microloader (Step 1). This is the root of trust. When the device boots, the microloader executes and validates the digital signature of the subsequent stage, typically the bootloader (Step 2). Once the bootloader is verified and active, it proceeds to validate the genuineness of the Cisco operating system image (Step 3). Only after all link in the chain are successfully verified is the operating system launched (Step 4).

Cisco Systems. "Cisco Trustworthy Systems: Secure Boot." Cisco Trustworthy Systems, Cisco Public.

Reference: Section "Secure Boot" and "Chain of Trust," describing the progression from the hardware anchor (microloader) to the bootloader and finally the OS verification.

Cisco Systems. "Cisco IOS XE Software Integrity Assurance - At-a-Glance." Cisco Public, 2020.

Reference: Diagram and text illustrating the "Hardware Anchor" → "Microloader" → "Bootloader" → "OS" verification flow.

The show telemetry transport command is used on a Cisco MDS 9000 Series switch to display the status of the transport session for SAN Telemetry Streaming (STS). This command provides critical information about the connection to the telemetry receiver, such as the destination IP address, port, and most importantly, the connection State. The state field will indicate if the session is ESTABLISHED, CONNECTING, or in another state, directly answering the question about the session's operational status.

A. show telemetry pipeline stats: This command displays performance statistics like the number of messages sent or dropped, not the active connection state of the telemetry session.
C. show telemetry control stats: This command shows statistics for telemetry control plane messages, which are used for managing the session, not the status of the data transport session itself.
D. show analytics system-load: This command is used to check the resource utilization (CPU, memory) of the SAN Analytics engine, which generates the data, not the telemetry transport status.

1. Cisco MDS 9000 Series NX-OS System Management Configuration Guide, Release 9.3(x)

Reference: Chapter: "Configuring SAN Telemetry Streaming", Section: "Verifying the SAN Telemetry Streaming Configuration".

Details: This section explicitly states, "To display the transport information for the telemetry, use the show telemetry transport command." It provides an example output where the State field clearly shows "ESTABLISHED", confirming its use for checking session status.

2. Cisco MDS 9000 Series Command Reference, Release 9.3(x)

Reference: Chapter: "Show Commands", Section: show telemetry transport.

Details: The command description confirms that it "Displays the transport information for the telemetry." The documentation for the other commands (show telemetry pipeline stats, show telemetry control stats) confirms they are for displaying statistics, not the transport connection state. The show analytics system-load command is documented in the SAN Analytics section, separate from telemetry verification.

Buffer-to-buffer flow control is a link-level mechanism that manages data flow between two adjacent Fibre Channel ports (port-to-port) using R_RDY primitives to prevent buffer overflow. Virtual Output Queues (VOQs) are a switching fabric architecture designed to eliminate Head-of-Line (HOL) blocking by maintaining separate queues for each egress port at the ingress side.

A Slow Port refers to the specific physical interface connected to a device that fails to accept frames at its line rate (often due to lack of B2B credits), creating backpressure. Slow Drain is the broader system condition or symptom where traffic fails to be transmitted at line rate across the fabric as a result of the congestion spreading from a slow device.

Cisco Systems, Cisco MDS 9000 Series High Availability Configuration Guide, "Architecture," Section: Virtual Output Queues (VOQs). (Defines VOQs as the mechanism to ensure HOL blocking prevention).

Broadcom (Brocade), Fabric OS Administrator's Guide, "Flow Control." (Defines Buffer-to-Buffer flow control as port-to-port management using buffer credits).

Cisco Systems, Troubleshooting and Mitigating Slow Drain in a Cisco Fabric, White Paper. (Distinguishes between the "Slow Drain" condition—congestion where traffic slows—and the "Slow Port" detection which identifies the specific device causing credit starvation).

T11 Committee (INCITS), Fibre Channel Framing and Signaling (FC-FS) Standards. (Technical definition of Buffer-to-Buffer flow control vs. End-to-End flow control).

The Cisco PowerOn Auto Provisioning (POAP) process automates the initial configuration and software installation of a new switch. When a Nexus switch boots without a startup configuration, it enters POAP mode. First, it sends a broadcast request using the Dynamic Host Configuration Protocol (DHCP) to obtain an IP address, default gateway, and the location of a provisioning script. The DHCP server responds with this information, typically pointing to a Trivial File Transfer Protocol (TFTP) server and a specific script filename. The switch then uses TFTP to download and execute this script, which completes the provisioning process. Therefore, both DHCP and TFTP are fundamental services required for POAP.

A. DNS is not a primary requirement for the initial POAP bootstrap, as the DHCP server can provide the TFTP server's IP address directly.
B. PXE is a preboot execution environment standard for servers and workstations, not the protocol used by the Cisco Nexus POAP feature.
C. BOOTP is a legacy protocol that has been largely replaced by DHCP. POAP relies on the more advanced features of DHCP.

1. Cisco Nexus 9000 Series NX-OS System Management Configuration Guide, Release 10.2(x), "Configuring PowerOn Auto Provisioning" section.

Reference: In the "About POAP" subsection, the process is described: "The switch sends out a DHCP discover message... The DHCP server replies with an IP address, TFTP server name, and a script file name. The switch configures the IP address on the interface and downloads the script file from the TFTP server." This explicitly confirms the requirement for both DHCP and TFTP.

2. Cisco Nexus 9000 Series NX-OS Fundamentals Configuration Guide, Release 9.3(x), "PowerOn Auto Provisioning" chapter.

Reference: The "POAP Process" section states, "When a Cisco Nexus 9000 Series device with the POAP feature boots and does not find a startup configuration, the device enters POAP mode, locates a DHCP server... The device also obtains the IP address of a TFTP server or the URL of an HTTP server and downloads a configuration script..." This confirms DHCP is the first step and TFTP (or HTTP) is the second. Since TFTP is an option, it is a correct choice.

When a subordinate switch joins a fabric, the principal switch assigns it a domain ID. If this dynamically assigned domain ID is not present in the subordinate switch's configured "allowed domain ID list" for that specific VSAN, the switch intentionally isolates the VSAN to prevent potential fabric instability. This results in all interfaces on that VSAN entering an isolated state. The direct solution is to modify the configuration on the subordinate switch to permit the assigned ID by adding it to the allowed list using the fcdomain allowed [domain-id] vsan [vsan-id] command. This allows the switch to accept the ID and join the fabric correctly.

B. Configuring a static domain ID is a different assignment method; it does not resolve the root cause, which is the allowed list filtering the dynamically assigned ID.
C. FICON is a specific protocol for mainframe connectivity and is irrelevant to resolving a standard Fibre Channel domain ID assignment and isolation issue.
D. IVR NAT is a feature used for routing traffic between different VSANs and does not address domain ID assignment problems within a single VSAN.

1. Cisco MDS 9000 Series Fabric Configuration Guide, Release 8.x, Chapter: "Configuring Fibre Channel Domains", Section: "Configuring the Allowed Domain ID List".

The document states, "By default, the allowed list includes all domain IDs. You can configure the allowed list of domain IDs for a VSAN to restrict the assignment of domain IDs to a switch. If the assigned domain ID is not in the allowed list, the VSAN on that switch is suspended." This directly supports that an unallowed ID causes isolation and that adding it to the list is the solution.

2. Cisco MDS 9000 Series System Messages Guide, Chapter: "FCSP Messages".

The explanation for the FCSP-3-VSANISOLATED system message often includes the reason "Domain id %d is not in the allowed list." The recommended action is to "Check the allowed domain ID list on the switch and add the assigned domain ID to the list if required." This confirms the problem and the corrective action.

3. Cisco Nexus 9000 Series NX-OS SAN Switching Configuration Guide, Release 10.4(x), Chapter: "Configuring Fibre Channel Domains", Section: "Allowed Domain ID List".

This guide provides a similar explanation: "If the assigned domain ID is not in the allowed list, the VSAN on that switch is isolated." This demonstrates the consistency of this behavior across Cisco SAN platforms.