VMware ESXi and vSphere Cluster Management

iSCSI Naming and Addressing: IQN and EUI Formats

Learn how iSCSI nodes use IQN and EUI names, how names differ from IP addresses and portals, and how to find an ESXi software iSCSI initiator name.

What iSCSI Names Identify

iSCSI means Internet Small Computer Systems Interface. It is a protocol for transporting SCSI commands over IP networks.

Every iSCSI node has a unique iSCSI name. An iSCSI node is a uniquely named iSCSI endpoint. The two common node types are:

Initiator: The client-side iSCSI node that starts storage sessions and requests access to target storage. An ESXi host's software iSCSI adapter is an example.
Target: The server-side iSCSI node that presents storage resources to initiators.

A stable node name is needed independently of network addressing. Network details can change because of DHCP, subnet changes, storage-network redesigns, failover, or multipathing. The node's identity should remain recognizable even when its connection endpoint changes.

Name versus address

Item	Purpose	Typical Form	Can It Change Without Renaming the Node?
Initiator or target name	Identifies the iSCSI node for discovery, sessions, access control, and storage presentation.	IQN or EUI, such as `iqn.1992-08.com.vmware:host-1`	Normally no. Changing it changes the node identity and may require target-side configuration updates.
Target portal address	Identifies a network-reachable target access point.	IP address or hostname, often paired with a port	Yes. The portal address can change while the target name remains the same.
TCP port	Identifies the transport endpoint used by the iSCSI service.	`3260` is the commonly used iSCSI TCP port	Yes, if the target and initiator are configured consistently.

An iSCSI portal is a network-reachable target access point, normally expressed through an IP address or hostname and a TCP port. A portal tells an initiator where to connect; the target's IQN or EUI tells it which iSCSI node it is connecting to. For example, iqn.1992-08.com.vmware:storage-array-1 identifies a target, while 192.0.2.40:3260 identifies a possible network endpoint for reaching it.

iSCSI Qualified Name (IQN)

An IQN, or iSCSI Qualified Name, is a structured iSCSI node naming format that begins with the fixed prefix iqn.. Its general structure is:

iqn.yyyy-mm.naming-authority:unique-name

iqn.: The fixed prefix identifying the IQN format.
yyyy-mm: The year and month when the naming authority was established. This is not necessarily the date when a device, host, or storage array was created.
naming-authority: The organization responsible for assigning names in that namespace. It commonly uses reversed Internet domain notation, such as com.vmware for a domain associated with vmware.com.
unique-name: A suffix assigned by the naming authority. It must prevent duplicate names within that authority's namespace.

The naming authority controls the convention for the final component. It might use a hostname, asset identifier, serial number, storage system identifier, or another locally unique value. Organizations should use consistent conventions and keep the complete name stable.

IQN construction example

Consider this illustrative IQN:

iqn.1992-08.com.vmware:host-1

Field	Meaning	Example Value	Administrative Guidance
Prefix	Identifies the IQN naming format.	`iqn.`	Keep the prefix exactly as specified.
Date	Identifies when the naming authority was established.	`1992-08`	Do not substitute the host or device creation date unless it also represents the authority establishment date.
Naming authority	Identifies the organization controlling the namespace.	`com.vmware`	Use the organization's established reversed-domain namespace.
Unique-name field	Identifies one node within that authority's namespace.	`host-1`	Assign a value that cannot collide with another initiator or target name.

The fields combine as iqn. + 1992-08 + com.vmware + :host-1. The result identifies one iSCSI node; it does not describe the node's IP address or TCP port.

Enterprise Unique Identifier (EUI)

EUI, or Enterprise Unique Identifier, is the second standard iSCSI naming format. Its general structure is:

eui.16-hex-digits

The fixed eui. prefix identifies the format. The suffix is a textual representation of a 64-bit IEEE Extended Unique Identifier. Because one hexadecimal digit represents four bits, exactly 16 hexadecimal characters represent 64 bits.

The 64-bit identifier has an allocation model consisting conceptually of:

First 24 bits: The IEEE-assigned company identifier, which identifies the organization.
Remaining 40 bits: A value assigned by that organization to identify a particular item or node.

When the identifier is allocated correctly, EUI names are designed to be globally unique. Administrators should not copy an EUI value from one system to another or invent a replacement without following the platform's naming rules.

EUI example and validation

Here is an illustrative EUI-style iSCSI name:

eui.5412369875AACDAF

This value is valid in the example because it has the eui. prefix followed by exactly 16 hexadecimal characters:

5412369875AACDAF contains 16 characters.
Each character is a decimal numeral from 0 through 9 or a hexadecimal letter from A through F.
Sixteen hexadecimal characters equal 16 × 4 = 64 bits.

Field	Bit Length	Meaning	Allocation Responsibility
IEEE company identifier portion	24 bits	Identifies the organization associated with the identifier.	Assigned through the IEEE identifier allocation system.
Organization-assigned unique identifier portion	40 bits	Identifies a value selected for a particular node or item within the organization's allocation.	Assigned and managed by the organization identified by the first 24 bits.

IQN versus EUI

Format	Pattern	Identity Source	Key Components	Example Use
IQN	`iqn.yyyy-mm.naming-authority:unique-name`	Human-readable naming authority and its namespace.	Fixed prefix, authority establishment date, reversed-domain authority, and locally unique suffix.	An administrator may identify an ESXi initiator with a readable host-specific name.
EUI	`eui.16-hex-digits`	IEEE-based 64-bit identifier.	Fixed prefix, 24-bit company identifier portion, and 40-bit organization-assigned portion.	A storage device or platform may advertise a compact numeric node identity.

Both IQN and EUI formats identify iSCSI nodes, but they are not interchangeable representations of the same name. An IQN cannot be converted into an EUI by changing its punctuation, and an EUI should not be rewritten as an IQN. Use the exact name advertised or configured by the storage system or initiator.

Viewing an ESXi Software iSCSI Adapter Name

A software iSCSI adapter is an ESXi host adapter that implements iSCSI in software and has an initiator name. The name is often needed when configuring target-side access controls, initiator groups, host groups, or LUN masking.

Select the ESXi host in the vSphere inventory.
Open the host's storage management area.
Open Storage Adapters.
Select the software iSCSI adapter.
Review the adapter status or adapter details area. The displayed iSCSI name is the ESXi initiator name.

Copy the complete displayed value, including its prefix, punctuation, and every character. On the storage target, add that exact IQN or EUI to the permitted initiator, host, or initiator-group configuration.

ESXi host adapter name  ->  target permitted-initiator list  ->  presented LUN access

Do not manually alter the name unless the ESXi or storage-platform documentation explicitly supports changing it. A changed name can leave existing access-control entries referring to the old identity.

Target-Side Access Configuration

Copy the initiator's full IQN or EUI exactly from the ESXi adapter details.
Add it to the storage target's permitted initiator, host, or initiator-group configuration.
Associate the appropriate target and LUN permissions with that entry.
Use the target's advertised iSCSI name, rather than its portal IP address, in fields that request a target identifier.

This distinction is important: a target IQN or EUI identifies the target node, while a target portal IP address tells the initiator where to establish a network connection.

Troubleshooting iSCSI Naming Problems

ESXi cannot access presented storage

Confirm that the initiator name entered on the target exactly matches the software iSCSI adapter's displayed name.
Check for omitted characters, extra characters, incorrect punctuation, or transcription errors.
Verify that the initiator was added to the correct target, host group, or LUN access policy.
Check platform-specific case-handling rules rather than assuming that different capitalization is harmless.

An IP address was entered where a node name is required

Portal addresses identify network connection endpoints. IQNs and EUIs identify iSCSI nodes. Use the target's advertised iSCSI name for discovery, access-control, or mapping fields that request a target identifier.

Two systems appear to have the same node name

Treat duplicate names as an identity and configuration conflict.
For IQNs, review the naming authority and the unique suffix.
For EUI names, verify that the identifier was allocated uniquely and was not copied between systems.
Correct the identity according to the platform's supported procedure, then update dependent access-control entries.

An EUI value is rejected

Confirm that the eui. prefix is present.
Confirm that exactly 16 hexadecimal characters follow the prefix.
Remove spaces and check for non-hexadecimal characters.
Compare the value with the source system to find transcription errors.

Key Points

Every iSCSI node, whether an initiator or target, has a unique node name.
Node names provide stable identity; IP addresses, portal addresses, and TCP ports provide connectivity details.
IQNs use a readable authority-and-date structure: iqn.yyyy-mm.naming-authority:unique-name.
EUIs use an IEEE-based 64-bit identifier: eui. followed by 16 hexadecimal characters.
Use the exact initiator name displayed by ESXi when configuring target-side access.
Use the target's advertised node name when a configuration field requests a target identifier, not merely the target portal address.

For the surrounding storage concepts, see iSCSI naming and addressing.