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How to Configure Multiple Independent IGP Instances of IS-IS and OSPFv2

Learn how to configure and run multiple instances of IGP on a router.

Configure Multiple IGP Instances of IS-IS

Learn about the benefits and get an overview of running multiple interior gateway protocol (IGP) instances of IS-IS on a router.

Benefits of Multi-Instance IS-IS

  • You can use multiple IGP instances of IS-IS to redistribute routes among independent IS-IS domains on a single router.
  • You can construct flexible IS-IS hierarchies across independent IGP domains.
  • Allows decoupling of multiple IS-IS flooding domains and therefore achieve a more scalable IS-IS deployment.
Figure 1: Multi-Instance IS-IS Deployment TopologyMulti-Instance IS-IS Deployment Topology

Figure 1 illustrates several benefits of configuring multiple IGP instances of IS-IS on the router. For example, Router F participates in two independent IS-IS instances. Router F treats IS-IS Aggregation Network-1 and IS-IS Core Network as two independent IGP domains, while at the same time redistributing routes between those domains. Network operators can use this flexibility to construct a hierarchy of IS-IS domains.

Figure 1 also illustrates the use of multiple IGP instances of IS-IS to separate metro networks into independent IS-IS flooding domains. In the example, routers D and E participate in the IS-IS metro-a, IS-IS metro-b, and IS-IS metro-c networks, as well as in IS-IS Aggregation Network-1. Routers D and E do not flood the different IS-IS domains with IS-IS advertisements. Instead they redistribute specific routes among the different IS-IS domains, which allows for more scalable metro deployments.

Multi-Instance IS-IS Overview

You can configure and run multiple independent IGP instances of IS-IS simultaneously on a router. These instances are associated with the default routing instance, and they install routes in the default routing table.Each IS-IS instance can also export the routes installed in the routing table by other IS-IS instances using the standard Junos OS routing policy configuration. By default, the routes installed by the different IS-IS instances have the same route preference.

Note:

Junos OS does not support configuring the same logical interface in multiple IGP instances of IS-IS.

In most deployment scenarios, only one IS-IS instance on a router installs a route for a given prefix. Therefore, you don't need to configure different route preferences for multiple IS-IS instances. However, for certain deployment scenarios where multiple IS-IS instances install the routes for the same prefix in the routing table, you can set a different route preference for the routes installed by other IS-IS instances. This allows the routing table to choose the routes with the best route preference and installs those routes in the forwarding table.

You can use the multiple IS-IS instance feature for both hierarchical and parallel deployments. In the case of hierarchical deployments, there are well-defined borders between the groups of routers participating in different IGP instances. In parallel deployments, different IGP instances (typically not more than two or three) span entire groups of routers. You can also have mixed deployments, with some domains in a hierarchical deployment running IGP instances in parallel.

You can configure multiple independent IGP instances of IS-IS by including the isis-instance configuration statement at the [edit protocols] hierarchy level. The configuration statements that you use at the [edit protocols isis-instance igp-instance-name] hierarchy level are the same as those available at the [edit protocols isis] hierarchy level.

Note:

The isis-instance configuration statement is not supported at the [edit routing-instances routing-instance-name protocols] hierarchy level.

You can configure multiple independent IGP instances of OSPFv2 by including the ospf-instance configuration statement at the [edit protocols] hierarchy level. The configuration statements that you use at the [edit protocols ospf-instance igp-instance-name] hierarchy level are the same as those available at the [edit protocols ospf] hierarchy level.

Note:

The ospf-instance configuration statement is not supported at the [edit routing-instances routing-instance-name protocols] hierarchy level.

You can configure and run multiple independent interior gateway protocol (IGP) instances of OSPFv2 with segment routing (SR) on a router. You can create two or more OSPF instances and apply SR-MPLS on each instance. Multiple instances of OSPF can advertise different prefix-segment identifiers (prefix-SIDs). Other instances can use these SIDs for making routing decisions.

Multi-instance OSPF combined with SR enhances network flexibility, scalability, and control over traffic engineering, especially in large and complex networks.

Example: Configure Independent IS-IS Instances in Metro Flooding Domains

Use this example to learn how to configure independent metro flooding domains running multiple IGP instances of IS-IS.

Overview

This example shows how to configure and run multiple independent IGP instances of IS-IS in metro flooding domains.

Topology

Figure 2 shows an example of metro flooding domains (metro-a and metro-b) running independent IGP instances of IS-IS. In the topology, routers R3 and R4 participate in metro IS-IS domains (IS-IS metro-a and IS-IS metro-b) and the IS-IS core network domain. Routers R3 and R4 do not flood the different IS-IS domains with IS-IS advertisements. Instead they redistribute specific routes among the different IS-IS domains, which allows for a more scalable metro deployment.

Figure 2: Multi-Instance IS-IS Topology Across Independent Metro Flooding Domains (IGP Domains)Network topology diagram showing IS-IS configuration: Metro domains with routers R1 and R2; Core network with routers R3, R4, R5, R6.

Requirements

This example uses the following hardware and software components:

  • MX Series routers
  • Junos OS Release 21.1R1 or later running on all devices
Note:

You must configure the network services mode as Enhanced IP. The Enhanced IP configuration ensures that the router uses enhanced mode capabilities.

After you configure the enhanced-ip statement and commit the configuration, the following warning message appears, prompting you to reboot the router:

The reboot brings up the FPCs on the router.

[See show chassis network-services.]

Configuration

To configure and run multiple IGP instances of IS-IS on the router, perform these tasks:

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Device R1

Device R2

Device R3

Device R4

Device R5

Device R6

Configure R1

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

You can use the steps in this example to also configure the R2, R5, and R6 routers. See CLI Quick Configuration and Figure 2 to understand the interface IDs, IP addresses, and the loopback addresses used on these routers.

To configure R1:

  1. Configure the interfaces to enable IP (inet) and ISO family support.

  2. Create the loopback interface and configure the IP and NET addresses.

  3. Configure routing options to identify the router in the domain.

  4. Enable IS-IS on the interfaces.

Results

From configuration mode, confirm your configuration by entering the show interfaces, show routing-options, and show protocols commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Configure R3

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

You can use the steps in this example to also configure the R4 router. See CLI Quick Configuration and Figure 2 to understand the interface IDs, IP addresses, and the loopback address used on the router.

To configure R3:

  1. Configure the interfaces connecting to R1, R2, and R5 to enable IP and ISO family support.

  2. Configure three subinterfaces (logical interfaces) connecting R3 and R4 (one IS-IS standard instance and two IS-IS metro instances (IS-IS metro-a and IS-IS metro-b)).

    Note:

    The standard IS-IS instance refers to the IS-IS IGP instance configured at the [edit protocols isis] hierarchy level.

  3. Create the loopback interface and configure the IP and NET addresses.

  4. Configure policies to redistribute loopback addresses of IS-IS metro-instance (IS-IS metro-a and IS-IS metro-b) and IS-IS standard-instance (core network) routers, so that the routes can be distributed across IS-IS domains as required.

    1. Configure policies to distribute the loopback address of R3.

    2. Configure policies to distribute the loopback addresses of the R5 and R6 routers (standard IS-IS instance).

    3. Configure policies to distribute the loopback addresses of R1 (IS-IS metro-a instance).

    4. Configure policies to distribute the loopback addresses of R2 (IS-IS metro-b instance).

  5. Enable IS-IS on the standard-instance interface (connecting R3 to R5) and on the subinterface (connecting R3 to R4).

  6. Configure IS-IS to export loopback addresses from IS-IS metro-a and IS-IS metro-b instances to the IS-IS standard instance. This configuration distributes specific routes instead of flooding the entire metro domain.

  7. Enable IS-IS on the IS-IS metro-b instance interface (connecting R3 to R2) and on the subinterface (R3 to R4).

  8. Configure IS-IS to export the loopback addresses of IS-IS metro-a and standard IS-IS instances to the IS-IS metro-b instance. This configuration distributes specific routes instead of flooding the entire standard IS-IS instances and metro-a domain instances.

  9. Enable IS-IS on the IS-IS metro-a instance interface (connecting R3 to R1) and on the subinterface (R3 to R4).

  10. Configure IS-IS to export the loopback addresses of IS-IS metro-b and standard IS-IS instances to the IS-IS metro-a instance. This configuration distributes specific routes instead of flooding the entire standard IS-IS instances and metro-b domain instances.

  11. Configure routing options to identify the router in the domain.

Results

From configuration mode, confirm your configuration by entering the show interfaces, show routing-options, and show protocols commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Verification

To verify that the configuration is working properly, perform the following tasks:

Verify IS-IS Advertisements

Purpose

Verify the IS-IS advertisement entries in the IS-IS link-state database (LSDB), which contains data about PDU packets.

Action

From operational mode, run the show isis database level 2 command.

On R3

On R1

Meaning

This output on R3 illustrates that R3 sees the IS-IS advertisements from R4, R5, and R6 which is standard IS-IS instance. R3 also sees the IS-IS advertisements from R1 (IS-IS metro-a), R2 (IS-IS metro-b), and R4 (both IS-IS metro-a and IS-IS metro-b). Thus, you can see that R3 is a common router that redistributes IS-IS routes among the IS-IS metro-a instance, the IS-IS metro-b instance, and the standard IS-IS instance (core network).

The output on R1 illustrates that R1 sees the IS-IS advertisements only from R3 and R4. R1 does not see any IS-IS advertisements from R2. Thus, you see that IS-IS metro-a and IS-IS metro-b are separate IS-IS flooding domains. You can use this property to build more scalable networks.

Verify the Routing Table

Purpose

Verify the route entries in the routing table.

Action

From operational mode, run the show route table inet.0 route-destination address extensive command.

On R3

Meaning

The output illustrates that the loopback address of R1 (192.168.100.1) is mapped to the IS-IS metro-a instance (IS-IS-metro-a) and the loopback address of R2 (192.168.100.2) is mapped to the IS-IS metro-b instance (IS-IS-metro-b) as configured in R3.

Verify the Routes in the IS-IS Routing Table

Purpose

Verify the routes in the IS-IS routing table.

Action

From operational mode, run the show isis route command.

On R3

On R1

Meaning

The output on R3 shows the loopback addresses and the IS-IS instance mapping information of R1, R2, R4, R5, and R6.

The output on R1 shows the loopback addresses of R2, R3, R4, R5, and R6.

Verify IS-IS Interfaces

Purpose

Verify the status information about IS-IS-enabled interfaces.

Action

From operational mode, run the show isis interface command.

On R3

On R1

Meaning

The output shows the interfaces mapped to different IS-IS instances.

Example: Configure Multiple Independent Instances of OSPFv2 with Segment Routing

Use this example to configure multiple IGP instances of OSPFv2 with segment routing.

Note:

Our content testing team has validated and updated this example.

Tip:
Table 1: Readability Score and Time Estimates

Reading Time

30 minutes

Configuration Time

20 minutes

Example Prerequisites

Hardware requirements

Three MX Series routers.

Software requirements

Junos OS Release 24.4R1 or later running on all devices.

Before You Begin

Benefits

Configuring multiple independent instances of OSPFv2 with segment routing enhances network flexibility, scalability, and control over traffic engineering, especially in large and complex networks.

Know more

Multiple Independent IGP Instances of OSPFv2

Functional Overview

Technologies used

  • Routing Protocols:OSPF

  • Segment Routing with Multiprotocol Label Switching (SR-MPLS)

  • VLAN Tagging

Primary verification tasks

  • Verify that multiple independent OSPF instances are running.

  • Verify the OSPF segment routing database for different prefix-SIDs advertised by the multiple instances of OSPF

Topology Overview

This configuration example depicts three devices R1, R2, and R3. There are two sub-interfaces configured between device R1 and device R2 and between device R2 and device R3. Each device runs multiple OSPF instances with segment routing enabled. We configure SR-MPLS to provide path control through the network. There are OSPF instances named metro-edge running on each of the two subinterfaces of the devices.

Hostname

Role

Function

R1, R2, and R3

The devices have multi-instance OSPF configured on the subinterfaces, with segment routing enabled.

The devices participate in OSPF multi-instances, advertise routes, and forward traffic using prefix-SIDs to other devices.

Topology Illustration

Figure 3:

R2 Configuration Steps

For complete sample configurations on R2, see: Appendix 1: Set Commands on All Devices

This section highlights the main configuration tasks needed to configure the R2 device for this example.

    1. Configure the basic device settings such as hostname, enhanced-ip mode, IPv4 addresses on the logical units of the device interfaces.

    2. Configure the loopback interface with an IP address and enable MPLS.

    3. Configure the router ID and autonomous system (AS) number to propagate routing information within a set of routing devices that belong to the same AS.

    4. Enable VLAN tagging and configure the logical units of both the interfaces with different VLAN IDs.

    5. Enable MPLS on each logical unit. Configure the maximum number of MPLS labels that can be applied to outgoing packets on logical units of each interface.

    6. Define a policy to load balance packets and apply the per-packet policy to enable load balancing of traffic.

    7. Configure a policy statement that matches routes based on the exact prefix and assign a segment identifier to the matched route.

    8. Configure MPLS traffic engineering, segment routing global block (SRGB) label range at the edit protocol mpls hierarchy level to ensure the labels are more predictable across segment routing domain, MPLS label range to assign labels from the configured srgb labels for the links.

  1. Configure the ospf-instance metro-edge on the subinterfaces (connecting from R2 to R1 and from R2 to R3).

  2. Enable the OSPF metro-edge instance to use segment routing with prefix-sids.

  3. Configure the IPv4 index value of the node segment.
  4. Configure the loopback address of the OSPF metro-edge instance as passive and disable the management interface (fxp0.0).

Verification

Command Verification Task
show route protocol ospf table inet.0 extensive
  • Verify the route entries in the routing table.

  • Verify the loopback address of R1 and R3 is mapped to the igp-instance as configured in R2.

show ospf spring sid-database igp-instance igp-instance Verify the OSPF segment routing database for the OSPF instance.
show ospf neighbor igp-instance igp-instance Verify neighbors for the specific OSPF instance.
show ospf database igp-instance igp-instance

Verify the OSPF advertisement entries in the OSPF link-state database (LSDB) associated with the IGP instance.

show ospf interface igp-instance igp-instance Verify the interfaces mapped to the IGP instance.
show ospf route igp-instance igp-instance Verify the routes and OSPF instance mapping information of R1 and R3.

Verify the Routing Table

Purpose

Verify the route entries in the routing table

Action

From operational mode, run the show route table inet.0 route-destination address extensive command.

Meaning

The output illustrates that the loopback address of R1 (10.1.255.1) and the loopback address of R3 (10.1.255.2) is mapped to the OSPF igp-instance metro-edge as configured in R2.

Verify OSPF Advertisements

Purpose

Verify the OSPF advertisement entries in the OSPF link-state database (LSDB) associated with the IGP instance.

Action

From the operational mode, run the show ospf database igp-instance igp-instance command.

Meaning

Verify the Routes in the OSPF Routing Table

Purpose

Verify the routes in the OSPF routing table

Action

From the operational mode, run the show ospf route command.

Meaning

The output on R2 shows the loopback addresses and OSPF instance mapping information of R1 and R3.

Verify the OSPF segment routing database

Purpose

Verify the OSPF segment routing database for the OSPF instance metro-edge.

Action

From the operational mode, run the show ospf spring sid-database igp-instance igp-instance command.

Meaning

The output illustrates the multiple instances of OSPF (metro-edge) advertise prefix-SIDs.

Verify the OSPF Interfaces

Purpose

Verify the status information about OSPF-instance enabled interfaces.

Action

From the operational mode, run the show ospf interface igp-instance igp-instance command.

Meaning

The output shows the subinterfaces of R2 mapped to the OSPF instances (metro-edge).

Verify the OSPF Neighbor

Purpose

Verify the adjacencies between the configured links.

Action

From the operational mode, run the show ospf neighbor igp-instance igp-instance command.

Meaning

Device R2 has established adjacency with Device R1 and Device R3 and as indicated by the State output field which is Full.

Appendix 1: Set Commands on All Devices

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

R1

R2

R3

Change History Table

Feature support is determined by the platform and release you are using. Use Feature Explorer to determine if a feature is supported on your platform.

Release
Description
change-completed
Starting in Junos OS and Junos OS Evolved Release 24.2R1, you can configure and run multiple independent IGP instances of OSPFv2 simultaneously on a router.
change-completed
Starting in Junos OS and Junos OS Evolved Release 24.4R1, you can configure and run multiple independent interior gateway protocol (IGP) instances of OSPFv2 with segment routing (SR) on a router.