Configure IS-IS Network Optimization

Configuration Condition

Before configuring the IS-IS adjustment and optimization, first complete the following tasks:

• Configure the IP address of the interface to enable the neighboring nodes to be reachable at the network layer.
• Enable the IS-IS protocol.

Configure IS-IS Interface Priority

The IS-IS chooses a node on the broadcast link as the DIS node. The DIS node sends the CSNP packet periodically to synchronize the link status database on the entire network. The Level-1 and Level-2 select the DIS node respectively. The interface with the highest priority is selected as the DIS node. The node with the large MAC address is selected as the DIS node for the nodes with the same priority.

Table 9-15: Configure the IS-IS interface priority

Configure IS-IS Passive Interface

The passive interface does not receive and transmit the IS-IS protocol packet, but still releases the directly connected network routing information of this interface. The IS-IS can reduce the bandwidth and CPU handling time through configuring the passive interface. Based on this configuration, the IS-IS can be specified to only release the directly connected network routing information of the passive interfaces and not release the directly connected network routing information of the non-passive interfaces.

Table 9-16: Configure the IS-IS passive interface

Configure IS-IS Hello Packet Parameter

1. Configure the Hello packet delivery interval.

The interface enabled with the IS-IS protocol will send the Hello packet to keep the neighboring relationship with the neighboring devices. The smaller delivery interval of the Hello packet is, the faster the network convergence is. However, more bandwidth will be occupied.

Table 9-17 Configure delivery interval for the Hello packet

2. Configure the number of invalid Hello packets.

The IS-IS calculates the neighbor relationship retention time based on the number of invalid Hello packets and informs the retention time to the neighboring device. If the neighboring device does not receive the Hello packet from this device during this period, the neighbor relationship is invalid and the routing calculation will be recalculated.

Table 9-18 Configure the number of invalid Hello packets

3. Configure to cancel the Hello packet padding function.

If MTU values on the interface at both sides of the link are inconsistent, as a result, smaller packets can be transmitted but larger packets cannot be transmitted. To avoid such situation, the IS-IS adopts the padding Hello packet to the interface MTU value to make the neighbor relationship cannot be established. However, this method wastes the bandwidth. In actual network, there is no need to configure the padding Hello packet. Only the small Hello packets are transmitted.

Table 9-19 Configure to cancel the Hello packet padding function

Configure IS-IS LSP Packet Parameter

1. Configure the maximum survival time for the LSP packet.

Each LSP packet has a maximum survival time. When the survival time of the LSP packet reduces to 0, the LSP packet will be deleted from the link status database. The maximum survival time of the LSP packet must be larger than the LSP packet refresh interval.

Table 9-20: Configure the IS-IS LSP packet parameter

2. Configure the LSP packet refresh interval.

The IS-IS protocol advertises and learns the routing through interacting each LSP packets. The nodes save the received LSP packets in the link status database. Each LSP packet has a maximum survival time and each node needs to refresh its LSP packet periodically to prevent the LSP packet maximum survival time reducing to 0 and keep the LSP packet in the entire area synchronization. Reducing the LSP packet delivery interval can accelerate the network convergence speed, but will occupy more bandwidth.

Table 9-21 Configure the LSP packet update packet

3. Configure the LSP packet generation interval.

Periodical refresh will generate new LSP packet. Besides, the interface status changes and network status changes will also trigger new LSP packet generation. To prevent frequently generated LSP packets occupying too much CPU resources, the user can configure the minimum LSP packet generation interval.

Table 9-22 Configure the LSP packet generation interval

4. Configure the LSP packet delivery interval.

Every generated LSP packet will be delivered on the interface. To avoid frequently generated LSP packet will greatly occupy the interface bandwidth. Each interface is configured with the minimum delivery interval of the LSP packet.

Table 9-23 Configure the LSP packet delivery interval

5. Configure the LSP packet retransmission time.

On the point-to-point link, the IS-IS sends the LSP packet and the then requires the peer end to send the PSNP acknowledgement message. If the IS-IS does not receive the acknowledgement message, the IS-IS will send the LSP packet again. The time waiting the acknowledgement message is the LSP packet retransmission interval. The retransmission interval can be set as required by the user to avoid LSP packet retransmission when the acknowledgement message is not received due to large delay.

Table 9-24: Configure the LSP packet retransmission time

6. Configure the LSP MTU value.

The IS-IS protocol packet cannot perform automatic fragmentation. In order not to affecting normal LSP packet spread, the maximum length of the LSP packet in a routing domain cannot exceed the minimum MTU value on the IS-IS interfaces of all devices. Therefore, when the interface MTU values are inconsistent on devices in the routing domain, it is recommended that the maximum length of the LSP packet is set uniformly.

Table 9-25 Configure the LSP MTU value

Configure IS-IS SNP Packet Parameter

1. Configure the CSNP packet delivery interval.

The selected nodes on the broadcast link need to send the CSNP packet periodically to synchronize the link status database on the entire network. The CSNP packet delivery interval is adjusted based on the actual situation.

Table 9-26: Configure the CSNP packet delivery interval

2. Configure the PSNP packet delivery interval

On the broadcast link, the PSNP packet synchronizes the link status database on the entire network. On the point-to-point link, the PSNP packet confirms the received LSP packet. To avoid a large number of PSNP packets being delivered over the interface. A minimum delivery interval is set for the PSNP packet and the user can change the interval dynamically. The PSNP packet delivery interval cannot be set to a too large value. If the packet delivery interval is set to a too large value, the link status database synchronization on the entire network will be affected for the broadcast link, and the LSP packet may be redelivered caused by not timely receiving the acknowledgment message for the point-to-point link.

Table 9-27 Configure the PSNP packet delivery interval

Configure IS-IS SPF Calculation Interval

The IS-IS link status database changes will trigger the SPF routing calculation. Frequent SPF calculation will consume a mass of CPU resources and user can configure the SPF calculation interval.

Table 9-28: Configure the IS-IS SPF calculation interval

Configure Maximum Number of Areas for IS-IS

Multiple area IP addresses can be configured in an IS-IS process. Multiple area IP addresses are mainly applied in the following two situations that multiple Level-1 areas are combined as a Level-1 area, or a Level-1 area is divided into multiple Level-1 areas.

Table 9-29: Configure the maximum number of areas for the IS-IS

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  This configuration must be consistent in the entire IS-IS Level-1 routing domain. Otherwise, the Level-1 neighbor cannot be established normally. The Level-2 neighbor is not affected.

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Configure IS-IS Host Name Mapping

The IS-IS uniquely identifies an intermediate system using the system ID with a fixed length of 6 bytes. When viewing the system information such as the neighbor relationship and link status database, the system ID cannot enable the user to visually associate the system ID with the host name. The IS-IS supports the mapping between the system ID and the host name to enable the user to view the system information more visually and conveniently. The IS-IS host name mapping can be configured in the following two methods:

1. Configure the IS-IS static host name mapping.

The IS-IS static host name mapping is manually established by the user between the system ID and the host name for the remote device.

Table 9-30 Configure the IS-IS static host name mapping

2. Configure the IS-IS dynamic host name mapping.

The static host name mapping requires the user to configure the system ID and host name mapping of other devices on each device in the network, which has a heavy workload. The dynamic host name mapping only configures the host name for each device, and other devices in the network can learn the host name of the device when the host name advertisement function is enabled.

Table 9-31 Configure the IS-IS dynamic host name mapping

Configure IS-IS Interface to Be Added to Mesh Group

When the IS-IS interface is not added to the mesh group, the LSP packet received from an interface will be sent out on all the other IS-IS interfaces. This results in great bandwidth waste in a full mesh connected network. To avoid this situation, several IS-IS interfaces can be added to a mesh group. When an interface receives the LSP packet, it only sends the LSP packet out to the interface that is not in the same mesh group with this interface.

Table 9-32: Configure the IS-IS interface to be added to the mesh group

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  The isis mesh-group blocked command can be used to configure the interface as the obstructive interface. The obstructive interface will not send the LSP packet actively and only send the LSP packet when receives the LSP request.

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