Internode Topology Discovery and Communication

This chapter describes how internode topology discovery and communication between NCS 1020 nodes takes place using OSPF.

Internode Topology Discovery and Communication

Optical applications on the NCS 1020 nodes must discover the OLT-OLT link topology. Span level applications must discover the adjacent nodes. Link level applications must learn the complete OLT-OLT link topology. NCS 1020 uses OSPF to discover the link topology and communicate topology information.

The networking devices running OSPF detect topological changes in the network, flood link-state updates to neighbors, and quickly converge on a new view of the topology. Each OSPF router in the network soon has the same topological view again.

Optical applications on NCS 1020 must discover the link topology, the different nodes and the node types, and the optical spectral band the nodes work on. NCS 1020 uses an enhanced version of OSPF that supports a new link-state advertisement attribute that advertises the node type and band.

Configure OSPF

The following commands are the necessary configurations for OSPF on an NCS 1020 OLT node.

configure

router ospf process-name

router-id router-id

distribute link-state​

network point-to-point​

area ​area-id

interface Loopback0​

interface GigabitEthernet0/0/0/0​

The following commands are the necessary configurations for OSPF on an NCS 1020 ILA node.

configure

router ospf process-name

router-id router-id

distribute link-state​

network point-to-point​

area ​area-id

interface Loopback0​

interface GigabitEthernet0/0/0/0​

interface GigabitEthernet0/0/0/2​


Important

You must configure router ID during OSPF configuration on NCS 1020 nodes.

See Implementing OSPF, for a description of the concepts and tasks necessary to implement OSPF on Cisco IOS XR.

Configure OSPF cost

Cost is the metric, you can use the cost command to explicitly specify the interface (network) for OSPF path calculation.

configure

router ospf process-name

router-id router-id

area ​area-id

interface Loopback0​

interface GigabitEthernet0/0/0/0​

cost cost

See cost (OSPF) for different command modes and usage guidelines to implement cost OSPF on Cisco IOS XR.


Note

The cost of the link is inversely proportional to the bandwidth of the link.

The following example shows a sample cost configuration. 

P/0/RP0/CPU0:ios(config)#router ospf 1 
 
RP/0/RP0/CPU0:ios(config-ospf)#area 0 
RP/0/RP0/CPU0:ios(config-ospf-ar)#interface Loopback0 
RP/0/RP0/CPU0:ios(config-ospf-ar-if)#interface GigabitEthernet0/0/0/0 
RP/0/RP0/CPU0:ios(config-ospf-ar-if)#cost 20 
RP/0/RP0/CPU0:ios(config-ospf-ar-if)#commit

IPv4-to-IPv6 topology migrations

A topology migration is a network transition procedure that

  • updates router and interface configurations to support IPv6 protocols,

  • verifies OSPFv3 adjacency and application continuity, and

  • removes legacy IPv4-specific parameters to complete the migration.

Migration sequence

To successfully migrate from IPv4 to IPv6, follow this sequence:

  1. Configure IPv6 router OSPF parameters on all nodes.

  2. Enable IPv6 on the Gigabit Ethernet interface.

  3. Configure an IPv6 address on the loopback interface.

  4. Verify that the OSPFv3 adjacency is in the FULL state.

  5. Remove the distribute link-state configuration from OSPFv2.

  6. Verify that the OLTs can see the end-to-end topology.

  7. Verify that the applications are working and have not been retriggered.

  8. Remove the IPv4-related configurations after the application verification.

Migrate a topology from IPv4 to IPv6

Enable IPv6 routing and ensure continued application and network visibility during topology migration.
Perform these steps to transition your existing network topology from IPv4 to IPv6 while maintaining uninterrupted operation and application access.

Before you begin

  • Ensure you have access to all network nodes.

  • Back up current configurations.

  • Verify network devices support IPv6 and OSPFv3.

Follow these steps to migrate the topology from IPv4 to IPv6:
Procedure

Step 1

Run the router ospfv3 1 command on each node, then run the router-id <router-id> command to configure its OSPFv3 router ID.

Example:

This sample shows the router ID configuration. 


RP/0/RP0/CPU0:ios(config)#router ospfv3 1
RP/0/RP0/CPU0:ios(config-ospfv3)#router-id 10.1.1.1
RP/0/RP0/CPU0:ios(config-ospfv3)#commit

This sample shows the router OSPFv3 configuration.


RP/0/RP0/CPU0:ios#show running-config router ospfv3
Thu Sep 24 18:35:09.649 IST
router ospf 1
 distribute link-state
 segment-routing mpls
 network point-to-point
 area 0 
  interface Loopback0 
  ! 
  interface GigabitEthernet0/0/0/0

Step 2

Run the ipv6 enable command to enable IPv6 on GigabitEthernet0/0/0/0 on both controllers of the ILA device.

Example:

This sample shows the IPv6 parameter for the Gigabit Ethernet interface.

RP/0/RP0/CPU0:ios(config)#interface gigabitEthernet 0/0/0/0 IPv6 enable

Step 3

Run the show running-config interface loopback command on Loopback0 to configure the IPv6 address.

Example:

This sample shows the IPv6 address on the loopback interface.


RP/0/RP0/CPU0:ios#show running-config interface loopback 0
interface Loopback0
 ipv6 address 2001:db8:1::1/128

Step 4

Run the show ospfv3 neighbor command to verify that the OSPFv3 adjacency is in the FULL state.

Example:

This sample shows an OSPFv3 neighbor in the FULL state.


RP/0/RP0/CPU0:ios#show ospfv3 neighbor
Neighbors for OSPFv3 1

Neighbor ID     Pri   State       Dead Time   Interface ID   Interface
10.1.1.2        1     FULL/ -     00:01:39    18             GigabitEthernet0/0/0/0


Neighbor is up for 00:41:56 
Total neighbor count: 1

Step 5

Run the no router ospf 1 distribute link-state command to remove the distribute link-state configuration from OSPFv2.

Example:

This sample shows the OSPFv2 configuration before removal.


RP/0/RP0/CPU0:ios#show running-config router ospf
Thu Sep 24 18:35:09.649 IST
router ospf 1
 distribute link-state

This sample removes the distribute link-state configuration. 


RP/0/RP0/CPU0:ios(config)#no router ospf 1 distribute link-state
RP/0/RP0/CPU0:ios(config)#commit

Step 6

Run the show olc topology command to verify end-to-end topology visibility to OLTs.

Example:

This sample shows the IPv6 topology. 


RP/0/RP0/CPU0:ios#show olc topology
Mon Jun 22 23:22:40.298 IST

Self RID: 10.1.1.4
Controller: Ots0/0/0/0

IPV6:
| Span ID | Span Type  | Local Node | Local RID  | Local Interface | Local IPv6-ID | Remote Node | Remote RID | Remote Interface | Remote IPv6-ID | OSC   |
|---------|------------|------------|------------|-----------------|---------------|-------------|------------|------------------|----------------|-------|
| 1       | Discovered | OLT        | 10.1.1.4   | GigE0/0/0/0     | 44            | ILA         | 10.1.1.3   | GigE0/0/0/2      | 18             | Up    |
| 2       | Discovered | ILA        | 10.1.1.3   | GigE0/0/0/0     | 17            | ILA         | 10.1.1.2   | GigE0/0/0/2      | 19             | Up    |
| 3       | Discovered | ILA        | 10.1.1.2   | GigE0/0/0/0     | 18            | OLT         | 10.1.1.1   | GigE0/0/0/0      | 45             | Up    |

Step 7

Run the show olc command in the example to verify that the applications have not been retriggered and are functional.

Example:

These are the commands to check the applications.


RP/0/RP0/CPU0:ios#show olc apc
RP/0/RP0/CPU0:ios#show olc raman-tuning
RP/0/RP0/CPU0:ios#show olc link-tuner
RP/0/RP0/CPU0:ios#show olc gain-estimator
RP/0/RP0/CPU0:ios#show olc span-loss
RP/0/RP0/CPU0:ios#show olc apc-local regulation-info

Step 8

After verifying application operation in Step 7, remove IPv4-related settings from the router ospf and interface configurations.

Run the no router ospf 1 command to remove the OSPFv2 router configuration, and commit the change. Run the no interface gigabitEthernet 0/0/0/0 ipv4 address command to remove the IPv4 address from the Gigabit Ethernet interface, and commit the change.

Example:

These samples show the OSPFv2 and Gigabit Ethernet removal commands.

RP/0/RP0/CPU0:ios(config)#no router ospf 1
RP/0/RP0/CPU0:ios(config)#commit

RP/0/RP0/CPU0:ios#no interface gigabitEthernet 0/0/0/0 ipv4 address
RP/0/RP0/CPU0:ios(config)#commit

These commands display the IPv4-related configurations before removal.


RP/0/RP0/CPU0:ios#show running-config router ospf 
Thu Sep 24 18:50:31.063 IST 
router ospf 1 
 distribute link-state 
 segment-routing mpls 
 network point-to-point 
 area 0 
  interface Loopback0 
  ! 
  interface GigabitEthernet0/0/0/0 


RP/0/RP0/CPU0:ios#show running-config interface gigabitEthernet 0/0/0/0  
Thu Sep 24 18:50:39.940 IST 
interface GigabitEthernet0/0/0/0 
 ipv4 point-to-point 
 ipv4 unnumbered Loopback0 

RP/0/RP0/CPU0:ios#show running-config interface loopback 0 
Thu Sep 24 18:50:49.310 IST 
interface Loopback0 
 ipv4 address 24.1.1.1 255.255.255.255
The network topology is migrated to IPv6, OSPFv3 is active, applications are running, and all IPv4-specific configurations have been removed. Network visibility and application functionality are maintained throughout the migration process.