Establishing an IS-IS Neighbor Relationship

Context

The methods to establish IS-IS neighbor relationships on a broadcast network and a P2P network are different. Therefore, you need to set different IS-IS attributes for interfaces of different types:

On a broadcast network, IS-IS needs to select a designated intermediate system (DIS). You can set DIS priorities for IS-IS interfaces to enable the device with the highest DIS priority to be elected as the DIS.
On a P2P network, IS-IS does not need to select the DIS. Therefore, the DIS priority does not need to be configured for interfaces. To ensure P2P link reliability, configure IS-IS to establish neighbor relationships on P2P interfaces in 3-way mode for unidirectional link fault detection.

Generally, IS-IS checks the IP addresses of received Hello packets. Neighbor relationships can be established only when the IP address carried in a received Hello packet and the address of the interface that receives the Hello packet are on the same network segment. If the IP addresses of the two P2P interfaces are on different network segments and the isis peer-ip-ignore command is run on the two interfaces, IS-IS does not check the peer IP address. The neighbor relationship can be correctly established on the two P2P interfaces.

Procedure

Establish an IS-IS neighbor relationship on a broadcast link.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. (Optional) On an Ethernet interface, run undo portswitch
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
4. Run ipv6 enable
  IPv6 is enabled on the interface.
5. Run isis ipv6 enable [ process-id ]
  IS-IS IPv6 is enabled on the interface.
  
  After this command is run, IS-IS establishes neighbor relationships and floods LSPs through this interface.
  
  Loopback interfaces are not used to establish neighbor relationships. If IS-IS is enabled on a loopback interface, IS-IS advertises the routes of the network segment where the interface resides through other IS-IS interfaces.
6. Run isis circuit-level [ level-1 | level-1-2 | level-2 ]
  A level is configured for the interface.
  
  By default, the level of an interface is Level-1-2.
  
  When two Level-1-2 devices establish an IS-IS neighbor relationship, they establish both Level-1 and Level-2 neighbor relationships. To allow the two Level-1-2 devices to establish only Level-1 or Level-2 neighbor relationship, change the level of interfaces.
  
  Changing the level of an IS-IS interface is valid only when the level of the IS-IS device is Level-1-2. If the level of the device is not Level-1-2, the level of the device determines the level of the established neighbor relationship.
7. (Optional) Run isis dis-priority priority [ level-1 | level-2 ]
  A DIS priority is set for the interface. A larger value indicates a higher priority.
  
  By default, the DIS priority of Level-1 and Level-2 broadcast interfaces is 64.
8. (Optional) Run isis silent [ advertise-zero-cost ]
  The interface is suppressed.
  
  By default, an IS-IS interface is not suppressed.
  
  When an IS-IS interface is suppressed, the interface no longer sends or receives IS-IS packets. The routes of the network segment where the interface resides, however, can still be advertised to other IS-IS devices within the same AS.
Establish an IS-IS neighbor relationship on a P2P link.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. (Optional) On an Ethernet interface, run undo portswitch
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
4. Run ipv6 enable
  IPv6 is enabled on the interface.
5. Run isis ipv6 enable [ process-id ]
  IS-IS IPv6 is enabled on the interface.
6. Run isis circuit-level [ level-1 | level-1-2 | level-2 ]
  A level is configured for the interface.
  
  By default, the level of an interface is Level-1-2.
7. Run isis circuit-type p2p [ strict-snpa-check ]
  The network type of the interface is set to P2P.
  
  By default, the network type of an interface is determined by the physical type of the interface.
  When the network type of an IS-IS interface changes, the interface configuration changes accordingly:
  - After a broadcast interface is simulated as a P2P interface using the isis circuit-type p2p [ strict-snpa-check ] command, the interval for sending Hello packets, number of Hello packets that IS-IS does not receive from a neighbor before the neighbor is declared Down, interval for retransmitting LSPs on a P2P link, and various IS-IS authentication modes are restored to the default settings; Other configurations such as the DIS priority, DIS name, and interval for sending CSNPs on a broadcast network become invalid.
  - After the undo isis circuit-type command is run to restore the default network type of an IS-IS interface, the interval for sending Hello packets, number of Hello packets that IS-IS does not receive from a neighbor before the neighbor is declared Down, interval for retransmitting LSPs on a P2P link, various IS-IS authentication modes, DIS priority, and interval for sending CSNPs on a broadcast network are restored to the default settings.
8. Run isis ppp-negotiation { 2-way | 3-way [ only ] }
  A negotiation mode is specified for the interface.
  
  By default, the negotiation mode is 3-way.
9. Run isis peer-ip-ignore
  IS-IS is configured not to check the IP addresses of received Hello packets.
  
  By default, IS-IS checks the IP addresses of received Hello packets.
10. Run isis ppp-osicp-check
  OSICP negotiation status check is configured on the interface.
  
  By default, the OSICP negotiation status of a PPP interface does not affect the status of an IS-IS interface.
  
  This command applies only to PPP interfaces and is invalid for other P2P interfaces.
  
  After this command is run, the OSICP negotiation status of a PPP interface affects the status of an IS-IS interface. When PPP detects that the OSI network fails, the link status of the IS-IS interface goes Down, and the routes of the network segment where the interface resides are not advertised through LSPs.