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Configuration Guide - IP Unicast Routing

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

This document describes the configurations of IP Unicast Routing, including IP Routing, Static Route, RIP, RIPng, OSPF, OSPFv3, IPv4 IS-IS, IPv6 IS-IS, BGP, Routing Policy, and PBR.
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Configuring Attributes for LSPs

Configuring Attributes for LSPs

Context

LSPs are used to exchange link state information. You can configure attributes for LSPs to control the length and maximum lifetime of LSPs. To accelerate network convergence, you can enable LSP fast flooding or reduce the minimum interval for sending LSPs and the interval for updating LSPs to speed up LSP flooding. However, CPU resources will be consumed too much if the network topology changes frequently. In this situation, configure the intelligent timer for generating LSPs. This timer can fast respond to emergencies, speed up network convergence, and improve CPU resource efficiency because its interval becomes longer when the network changes frequently.

Configured Parameters

Function

Usage Scenario

Set the maximum length for LSPs

Set the size for LSPs to be generated and LSPs to be received.

When the volume of link status information increases, the length of LSPs to be generated can be increased to carry more information in each LSP.

Set the maximum lifetime for LSPs

Set the maximum lifetime for LSPs to ensure the validity of an LSP before its updated LSP is received.

When a switch generates the system LSP, it fills in the maximum lifetime for this LSP. After this LSP is received by other switches, the lifetime of the LSP is reduced gradually. If the switch does not receive any more update LSPs and the lifetime of the LSP is reduced to 0, the LSP will be deleted from the LSDB 60s later if no more updated LSPs are received.

Set the refresh interval for LSPs

Set the refresh interval for LSPs to synchronize LSDBs.

On an IS-IS network, LSDB synchronization is implemented through LSP flooding. During LSP flooding, a switch sends an LSP to its neighbors and then the neighbors send the received LSP to their respective neighbors except the switch that first sends the LSP. In this manner, the LSP is flooded among the switches of the same level. LSP flooding allows each switch of the same level to have the same LSP information and synchronize its LSDB with each other.

Set the maximum holdtime for the largest IS-IS route cost in local LSPs

Set the maximum holdtime for the largest IS-IS route cost in local Link State PDUs (LSPs).

When a Down IS-IS interface goes Up, IS-IS neighbor relationships are re-established on the interface, and traffic is switched back to this Up interface after IGP route convergence. IGP route convergence is fast, but many services that depend on IGP routes may not expect such fast traffic switchback. To delay traffic switchback after IGP route convergence, set the maximum holdtime for the largest IS-IS route cost (16777214 in wide mode and 63 in narrow mode) in local LSPs. In this manner, before the specified maximum holdtime expires, traffic is not switched back to this route due to its large cost. After the specified maximum holdtime expires, the route cost reverts to the original value, and then traffic is switched back to this route.

Set the minimum interval at which LSPs are sent

Set the interval for sending an LSP during LSP update.

Reducing the minimum interval for sending LSPs speeds up LSP flooding.

Configure the intelligent timer used to generate LSPs

Control the interval for generating LSPs intelligently to speed up route convergence and reduce system load.

On an IS-IS network, if the local routing information changes, a switch needs to generate a new LSP to notify this change. If the local routing information changes frequently, a large number of new LSPs are generated, which occupies a lot of system resources and decreases system performance. To speed up network convergence and prevent system performance from being affected, configure an intelligent timer for generating LSPs. This timer can adjust the delay in generating LSPs based on the routing information change frequency.

Enable LSP fast flooding

Control the number of LSPs flooded each time on an interface to speed up IS-IS network convergence.

When an IS-IS switch receives new LSPs from other switches, it switch updates the LSPs in the local LSDB and periodically floods out the updated LSPs according to a timer. LSP fast flooding updates the preceding method. When a device configured with LSP fast flooding receives one or more new LSPs. It floods out the LSPs with a number smaller than the specified number before calculating routes. This speeds up LSDB synchronization.

Set an interval at which LSPs are retransmitted over a P2P link

Control the interval for retransmitting LSPs to ensure LSDB synchronization on a P2P network.

On a point-to-point network, devices at both ends of a link synchronize LSDBs with each other by flooding LSPs. The device at one end of the link sends an LSP. If the device at the other end receives this LSP, it replies with a PSNP. If the device that has sent an LSP does not receive a PSNP from the other end in a period of time, the device will retransmit the LSP.

Procedure

  • Set the maximum length for LSPs.
    1. Run system-view

      The system view is displayed.

    2. Run isis [ process-id ]

      The IS-IS view is displayed.

    3. Set the maximum length for LSPs.

      • Run lsp-length originate max-size

        The maximum length is set for each generated LSP.

      • Run lsp-length receive max-size

        The maximum length is set for each received LSP.

      By default, the IS-IS system generates and receives 1497-byte LSPs.

      NOTE:

      Ensure that the value of max-size for LSPs to be generated must be smaller than or equal to the value of max-size for LSPs to be received.

      The value of max-size set through the lsp-length command must meet the following requirements; otherwise, the MTU status on the interface is considered Down.
      • The MTU of an Ethernet interface must be greater than or equal to the sum of the value of max-size and 3.

      • The MTU of a P2P interface must be greater than or equal to the value of max-size.

    4. Run commit

      The configuration is committed.

  • Set the maximum lifetime for LSPs.
    1. Run system-view

      The system view is displayed.

    2. Run isis [ process-id ]

      The IS-IS view is displayed.

    3. Run timer lsp-max-age age-time

      The maximum lifetime is set for LSPs.

      By default, the maximum lifetime of LSPs is 1200 seconds.

    4. Run commit

      The configuration is committed.

  • Set the refresh interval for LSPs.
    1. Run system-view

      The system view is displayed.

    2. Run isis [ process-id ]

      The IS-IS view is displayed.

    3. Run timer lsp-refresh refresh-time

      A refresh interval is set for LSPs.

      By default, the LSP refresh interval is 900s.

      NOTE:

      Ensure that the LSP refresh interval is more than 300s shorter than the maximum LSP lifetime. This allows new LSPs to reach all devices in an area before existing LSPs expire.

      The larger a network, the greater the deviation between the LSP refresh interval and the maximum LSP lifetime.

    4. Run commit

      The configuration is committed.

  • Set the maximum holdtime for the largest IS-IS route cost in local LSPs.
    1. Run system-view

      The system view is displayed.

    2. Run interface interface-type interface-number

      The interface view is displayed.

    3. Run isis peer hold-max-cost timer timer

      The maximum holdtime for the largest IS-IS route cost in local LSPs is set.

      By default, no maximum holdtime is set for the largest IS-IS route cost in local LSPs.

      NOTE:

      The effective time of the specified maximum holdtime is different for P2P and broadcast neighbors.

      • For a P2P neighbor, the maximum holdtime takes effect after the neighbor relationship goes Up.
      • For a broadcast neighbor, the maximum holdtime takes effect after the neighbor relationship goes Up and then a DIS is elected successfully.

    4. Run commit

      The configuration is committed.

  • Set the minimum interval at which LSPs are sent.
    1. Run system-view

      The system view is displayed.

    2. Run interface interface-type interface-number

      The interface view is displayed.

    3. (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.

      If an Ethernet interface already has Layer 2 configuration, this command fails to be executed on the interface. Before running this command on the interface, delete all the Layer 2 configuration of the interface.

      NOTE:

      If many Ethernet interfaces need to be switched to Layer 3 mode, run the undo portswitch batch interface-type { interface-number1 [ to interface-number2 ] } &<1-10> command in the system view to switch these interfaces to Layer 3 mode in batches.

    4. Run isis timer lsp-throttle throttle-interval [ count count ]

      The minimum interval for sending LSPs on an IS-IS interface and the maximum number of LSPs sent within the interval are set.

      By default, the minimum interval for sending LSPs is 50 ms, and the maximum number of LSPs sent each time is 10.

    5. Run commit

      The configuration is committed.

  • Configure the intelligent timer used to generate LSPs.
    1. Run system-view

      The system view is displayed.

    2. Run isis [ process-id ]

      The IS-IS view is displayed.

    3. Run timer lsp-generation max-interval [ init-interval [ incr-interval ] ] [ level-1 | level-2 ]

      The intelligent timer used to generate LSPs is set.

      If no level is configured, both Level-1 and Level-2 are configured.

      By default, the maximum delay in generating LSPs is 2 seconds.

      The intelligent timer involves three parameters, and the parameters are described as follows:
      • When only max-interval is specified, the intelligent timer functions as an ordinary one-time triggering timer.
      • When both init-interval and incr-interval are specified, the delay in generating an LSP for the first time is determined by init-interval, and the delay in generating an LSP with the same LSP ID for the second time is determined by incr-interval. Subsequently, each time routes change, the delay in generating an LSP doubles the last delay until the delay reaches the value specified by max-interval.
      • When init-interval is specified but incr-interval is not, the delay in generating an LSP for the first time is determined by init-interval, and the delay in generating subsequent LSPs is determined by max-interval.

    4. Run commit

      The configuration is committed.

  • Enable LSP fast flooding.
    1. Run system-view

      The system view is displayed.

    2. Run isis [ process-id ]

      The IS-IS view is displayed.

    3. Run flash-flood [ lsp-count | max-timer-interval interval | [ level-1 | level-2 ] ] *

      The LSP fast flooding is enabled.

      The lsp-count parameter specifies the number of LSPs flooded each time, which is applicable to all interfaces. If the number of LSPs to be sent is greater than the value of lsp-count, lsp-count takes effect. If the number of LSPs to be sent is smaller than the value of lsp-count, LSPs of the actual number are sent. If a timer is configured and the configured timer does not expire before the route calculation, the LSPs are flooded immediately when being received; otherwise, the LSPs are sent when the timer expires.

      When LSP fast flooding is enabled, Level-1 LSPs and Level-2 LSPs are fast flooded by default if no level is specified.

    4. Run commit

      The configuration is committed.

  • Set an interval at which LSPs are retransmitted over 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. (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.

      If an Ethernet interface already has Layer 2 configuration, this command fails to be executed on the interface. Before running this command on the interface, delete all the Layer 2 configuration of the interface.

      NOTE:

      If many Ethernet interfaces need to be switched to Layer 3 mode, run the undo portswitch batch interface-type { interface-number1 [ to interface-number2 ] } &<1-10> command in the system view to switch these interfaces to Layer 3 mode in batches.

    4. (Optional) Run isis circuit-type p2p

      A broadcast interface is simulated as a P2P interface.

      NOTE:

      If the interface type is P2P, this step is not required.

    5. Run isis timer lsp-retransmit retransmit-interval

      The interval at which LSPs are retransmitted over a P2P link is set.

      By default, the interval for retransmitting LSPs over a P2P link is 5 seconds.

    6. Run commit

      The configuration is committed.

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Updated: 2019-04-20

Document ID: EDOC1100074760

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