In which configuration mode is net [NSAP-address] used?

The net [NSAP-address] command is entered in IS-IS Config mode on Cisco IOS-XR devices.

isisIS-IS Config

net [NSAP-address]

Configures a NET (Network Entity Title) for IS-IS routing on Cisco IOS-XR.

Definition: net [NSAP-address] is a Cisco IOS-XR is-is config command. Configures a NET (Network Entity Title) for IS-IS routing on Cisco IOS-XR.

Overview

The 'net' command in Cisco IOS-XR IS-IS configuration mode is used to assign a Network Entity Title (NET) to the IS-IS routing process. The NET is an NSAP address that identifies the router in the IS-IS network. It consists of three parts: the Area ID (variable length), the System ID (6 bytes), and the NSAP Selector (1 byte, always 00 for IS-IS).

The NET uniquely identifies the router within an area and is essential for IS-IS operation. Without a NET, the IS-IS process cannot form adjacencies or exchange routing information. This command is typically used during initial IS-IS configuration or when renumbering the network.

On IOS-XR, the NET is configured under the IS-IS router configuration mode, and multiple NETs can be specified for multi-area support, but all must share the same system ID. The command is straightforward but critical; misconfiguration can lead to adjacency failures or routing loops. In troubleshooting workflows, verifying the NET with 'show isis' is a first step when IS-IS adjacencies are not forming.

Syntax·IS-IS Config

net [NSAP-address]

When to Use This Command

Assigning a NET to an IS-IS instance to enable routing in a Level-1 area.
Configuring a Level-2 router with a NET that includes a unique system ID.
Setting up multi-area IS-IS with separate NETs for Level-1 and Level-2.
Replacing an existing NET during network renumbering or migration.

Parameters

Parameter	Syntax	Required	Description
NSAP-address	XX.XXXX.XXXX.XXXX.XX	Required	The NSAP address in dotted format. It includes the area ID, system ID, and selector. The system ID must be unique per router. The selector must be 00 for IS-IS.

Command Examples

Basic NET Configuration

net 49.0001.1921.6800.1001.00

Configures a NET with area ID 49.0001, system ID 1921.6800.1001, and selector 00.

Verifying NET Configuration

show isis

IS-IS Router: test
  System Id: 1921.6800.1001
  IS-Type: level-1-2
  Area Address(es):
    49.0001
  NET: 49.0001.1921.6800.1001.00
  ...

Displays the configured NET and associated parameters.

Understanding the Output

The 'show isis' command output displays the configured NET under the 'NET' field. The NET consists of three parts: the Area ID (e.g., 49.0001), the System ID (e.g., 1921.6800.1001), and the NSAP Selector (always 00 for IS-IS). The System ID uniquely identifies the router within the area.

A healthy configuration shows a single NET with correct area and system ID. Problems include missing NET, duplicate system IDs in the same area, or incorrect area ID causing adjacency failures.

Configuration Scenarios

Single Area IS-IS

Configuring a router in a single Level-1 area.

Topology

Router A (NET: 49.0001.1921.6800.1001.00) --- Router B (NET: 49.0001.1921.6800.1002.00)

Steps

1.Enter IS-IS configuration mode: router isis test
2.Configure NET: net 49.0001.1921.6800.1001.00
3.Commit the configuration: commit

Configuration

router isis test
 net 49.0001.1921.6800.1001.00
 commit

Verify: Use 'show isis' to verify NET and 'show isis adjacency' to check neighbor formation.

Watch out: Ensure the area ID matches on both routers; otherwise, adjacencies won't form.

Multi-Area IS-IS

Configuring a Level-1-2 router with multiple area addresses.

Topology

Router X (NET: 49.0001.1921.6800.1001.00, Area: 49.0002) --- Router Y (NET: 49.0002.1921.6800.1002.00)

Steps

1.Enter IS-IS configuration: router isis test
2.Configure primary NET: net 49.0001.1921.6800.1001.00
3.Add additional area: area 49.0002
4.Commit

Configuration

router isis test
 net 49.0001.1921.6800.1001.00
 area 49.0002
 commit

Verify: Check 'show isis' to see multiple area addresses.

Watch out: The system ID must be the same across all NETs; only the area ID changes.

Troubleshooting with This Command

When IS-IS adjacencies fail, the first step is to verify the NET configuration using 'show isis'. Ensure the NET is present and correctly formatted. Common issues include missing NET, incorrect area ID, or duplicate system IDs.

Use 'show isis adjacency' to see if neighbors are attempting to form. If the NET is correct but adjacencies still fail, check interface configuration and IS-IS levels. On IOS-XR, the NET must be committed; if not, it won't take effect.

Also, verify that the system ID is unique within the area; duplicate system IDs cause routing instability. Use 'show isis database' to check for LSPs with conflicting system IDs. If multiple NETs are configured, ensure they all share the same system ID.

Finally, check the IS-IS process status with 'show isis process' to confirm the process is running.

CCNA Exam Tips

Remember that the NET must end with .00 for IS-IS.

The system ID is typically derived from the router's MAC or loopback IP.

In CCNP exams, know that a router can have multiple NETs but only one system ID.

Common Mistakes

Forgetting the trailing .00 in the NET (causes configuration rejection).

Using the same system ID in different areas (causes routing issues).

Configuring multiple NETs with different system IDs (not allowed).

net [NSAP-address] vs address-family ipv4 unicast

In Cisco IOS-XR IS-IS configuration, the net command defines the Network Entity Title (NET) to identify the router, while the address-family ipv4 unicast command enters the IPv4 unicast sub-mode to configure routing policies and interfaces. Both are configured under the IS-IS router process but serve distinct roles, leading to confusion for beginners.

Aspect	net [NSAP-address]	address-family ipv4 unicast
Scope	Sets the NET (area ID and system ID) for the router	Configures IPv4 unicast routing parameters and interfaces
Configuration Mode	Executed directly under router isis configuration mode	Enters sub-mode (config-isis-af) for IPv4 unicast
Persistence	Saved to running-config and startup-config	Saved to running-config and startup-config
Precedence	Must be configured before address-family can become fully operational	Can be configured at any time, but requires NET for LSP generation
Typical Use	Defines router identity and IS-IS area membership	Enables IPv4 routing on interfaces and sets redistribution

Use net [NSAP-address] when initially setting up IS-IS or changing the router's area or system ID.

Use address-family ipv4 unicast when customizing IPv4 routing behavior, such as enabling interfaces or redistributing routes.

Platform Notes

On Cisco IOS-XR, the 'net' command is used under IS-IS router configuration mode, similar to IOS. However, IOS-XR requires explicit 'commit' to apply changes. Unlike IOS, IOS-XR supports multiple NETs for multi-area configurations, but all must have the same system ID.

The NSAP address format is the same as IOS. In IOS-XR, the NET can be removed with 'no net' but the system ID remains. For equivalent commands on other platforms, Juniper uses 'set protocols isis net' and Nokia uses 'isis net'.

Version differences: In older IOS-XR releases, the NET command was part of the 'router isis' configuration; newer releases maintain the same syntax.

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