SonicOS 8 IPv6 Interface Identifier Configuration
Description
When a SonicWall interface is configured to use stateless address autoconfiguration (SLAAC), the IPv6 address is formed by combining a network prefix (received from the upstream router via Router Advertisement) with a host-portion suffix. By default, SonicOS derives this suffix automatically from the interface's MAC address using the EUI-64 algorithm.
SonicOS 8 allows administrators to replace the auto-generated EUI-64 suffix with a custom Interface Identifier. This gives administrators full control over the host portion of SLAAC-derived IPv6 addresses, useful when ISP provisioning requirements mandate a specific identifier, or when a stable, predictable address is needed across prefix changes.
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SonicOS 8: When a custom Interface Identifier is configured, SonicOS uses the specified value as the 64-bit host-portion suffix for all SLAAC-derived IPv6 addresses on that interface. The network prefix continues to be received from the RA. The resulting address is: <RA prefix> + <configured Interface Identifier>. |
How It Works
A standard IPv6 address is 128 bits long, split evenly between a 64-bit network prefix and a 64-bit host identifier (the Interface Identifier). In SLAAC operation:
- The network prefix is received from the upstream router via Router Advertisement (RA).
- The host identifier is normally derived from the interface's MAC address using the EUI-64 algorithm, producing a value that is unique to the hardware but not administrator-controlled.
With the Interface Identifier configuration, the EUI-64 derived value is replaced by a fixed value specified by the administrator. The address construction remains the same, only the host portion changes.
Where the Setting Appears
The Interface Identifier field location depends on the IP Assignment mode configured for the interface:
Auto Mode
When IP Assignment is set to Auto, the Interface Identifier field is displayed on the Advanced Tab, under the Advanced Settings section.
Static Mode
When IP Assignment is set to Static, the Interface Identifier field appears on the Advanced Tab, below the Enable Listening to Router Advertisement and Enable Stateless Address Autoconfiguration toggles.
Important: In Static mode, the Interface Identifier field is only active when both Enable Listening to Router Advertisement and Enable Stateless Address Autoconfiguration are toggled on. If either toggle is disabled, the field is inactive and the custom identifier is not applied.
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Format: Enter the Interface Identifier as the host-portion suffix only, using double-colon notation. Example: ::1111:2222:3333:4444 Do not enter a full IPv6 address. SonicOS automatically combines the configured suffix with the prefix received from the RA to form the complete 128-bit IPv6 address. |
Configuration
For step-by-step configuration instructions, refer to the SonicOS 8 Administration Guide.
Real-World Use Cases
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Use Case |
Scenario |
Outcome |
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ISP Provisioning Requirement |
An ISP requires the customer firewall's WAN interface to use a specific host identifier as part of its IPv6 address. The auto-generated EUI-64 value does not meet this requirement. |
The administrator configures the Interface Identifier field on the WAN interface with the ISP-specified value. SonicOS uses this value as the host portion of the SLAAC-derived address, satisfying the ISP provisioning requirement. |
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Stable Address Across Prefix Changes |
An ISP periodically reassigns the WAN IPv6 prefix. Each reassignment changes the full interface address, making it difficult to maintain consistent policy rules or DNS records that reference the WAN IPv6 address. |
By configuring a fixed Interface Identifier, the host portion of the WAN IPv6 address remains constant across prefix changes. Only the network prefix portion changes when the ISP reassigns it, keeping address management predictable. |
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Replacing EUI-64 for Privacy or Security |
An organization's security policy prohibits embedding MAC addresses in publicly visible IPv6 addresses. The default EUI-64 algorithm encodes the MAC address directly into the interface identifier. |
The administrator configures a custom Interface Identifier that does not derive from the MAC address. This satisfies the security policy while maintaining SLAAC operation. |
Summary
SonicOS 8 allows administrators to configure a custom Interface Identifier as the host-portion suffix for SLAAC-derived IPv6 addresses. When set, this value replaces the auto-generated EUI-64 suffix. The setting is available on the Advanced Tab of the interface, under Advanced Settings in Auto mode, and below the RA/SLAAC toggles in Static mode (active only when both toggles are enabled). The Interface Identifier is entered as a suffix in double-colon notation, and SonicOS combines it with the RA-advertised prefix to form the complete IPv6 address.
