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ME60 V800R010C10SPC500 Configuration Guide - IP Routing 01

This is ME60 V800R010C10SPC500 Configuration Guide - IP Routing
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Preventing Routing Loops

Preventing Routing Loops

RIPng is a distance vector routing protocol. Because RIPng devices advertise their routing tables to their neighbors, routing loops may occur.

Usage Scenario

RIPng prevents routing loops by using the following mechanisms:
  • Counting to infinity: RIPng defines the cost of 16 as infinity. If the cost of a route reaches 16 due to a routing loop, this route is considered unreachable.
  • Split horizon: Split horizon prevents a RIPng-enabled interface from sending back the routes it learns, which reduces bandwidth consumption and prevents routing loops.
  • Poison reverse: Poison reverse allows a RIPng-enabled interface to set the cost of the route that it learns from a neighbor to 16 (indicating that the route is unreachable) and then send the route back. After receiving this route, the neighbor deletes the useless route from its routing table, which prevents loops.
  • Suppression timers: Suppress timers can prevent routing loops and reduce the possibility that receiving incorrect routes results in incorrect routing information.
NOTE:

If both split horizon and poison reverse are configured, only poison reverse takes effect.

Pre-configuration Tasks

Before configuring RIPng to prevent routing loops on the network, complete the following tasks:

Configuration Procedure

Perform one or more of the following configurations as required.

Configuring Split Horizon

You can configure split horizon to prevent routing loops.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run interface interface-type interface-number

    The interface view is displayed.

  3. Run ripng split-horizon

    Split horizon is enabled.

    If both split horizon and poison reverse are configured, only poison reverse takes effect.

  4. Run commit

    The configuration is submitted.

Configuring Poison Reverse

You can configure poison reverse to prevent routing loops.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run interface interface-type interface-number

    The interface view is displayed.

    If both split horizon and poison reverse are configured, only poison reverse takes effect.

  3. Run ripng poison-reverse

    Poison reverse is enabled.

  4. Run commit

    The configuration is submitted.

Configuring Suppression Timers

Suppression timers can prevent routing loops and reduce the possibility that receiving incorrect routes results in incorrect routing information.

Context

When hop count of a route increases, a device starts suppression timers and accepts the Update packet of this route and updates the routing table until the suppression timers expire.

Suppression timers delays the addition of incorrect routes to the routing Table and slows down route convergence on the entire network as well. Therefore, exercise caution when configuring the suppression timers.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run ripng process-id

    The RIPng process is created, and the RIPng view is displayed.

  3. Run timers ripng update age suppress garbage-collect

    Suppression timers are set.

  4. Run commit

    The configuration is submitted.

Follow-up Procedure

RIPng has four timers: update, age, suppress, and garbage-collect. The value of update is less than that of age, and the value of suppress is less than that of garbage-collect. Setting improper values for the timers affects RIP convergence speed and even causes route flapping on the network. For example, if the value of update is greater than that of age, a device cannot inform its neighbors of the change of RIP routes immediately.

For the configurations of update, age, suppress, and garbage-collect, see Configuring RIPng Timers.

Verifying the Configuration of Routing Loop Prevention

After configuring routing loop prevention, verify the running status of RIPng, information about interfaces, and RIPng routing information.

Prerequisites

Routing loop prevention has been configured.

Procedure

  • Run the display ripng [ process-id | vpn-instance vpn-instance-name ] command to check the current operating status and configuration of RIPng.
  • Run the display ripng process-id route [ destination-address destination-address [ mask-length ] ] [ interface interface-type interface-number [ neighbor-address neighbor-address ] ] command to check RIPng routes.
  • Run the display ripng process-id interface command to check information about RIPng interfaces.

Example

Run the display ripng command to view the current operating status and configuration of the RIPng process.

<HUAWEI> display ripng
  Public vpn-instance name :
    RIPng process : 100
       Preference : 100
       Checkzero : Enabled
       Default Cost : 0
       Maximum number of balanced paths : 6
       Update time   : 30 sec   Age time  : 180 sec
       Suppress time : 0 sec    Garbage-Collect time : 120 sec
       Number of periodic updates sent : 0
       Number of trigger updates sent : 1
       Number of routes in database : 1
       Number of interfaces enabled : 1

Run the display ripng process-id route command to view all the routes learned by the RIPng process.

<HUAWEI> display ripng 100 route
   Route Flags: A - Aging, S - Suppressed, G - Garbage-collect
 ----------------------------------------------------------------

 Peer FE80::200:5EFF:FE04:B602  on GigabitEthernet6/0/0
 Dest 2001:DB8:C18:1::/64,
     via FE80::200:5EFF:FE04:B602, cost  2, tag 0, A, 34 Sec
 Dest 2001:DB8:C18:2::/64,
     via FE80::200:5EFF:FE04:B602, cost  2, tag 0, A, 34 Sec
 Peer FE80::200:5EFF:FE04:B601  on GigabitEthernet6/0/0
 Dest 2001:DB8:C18:1::/64,
     via FE80::200:5EFF:FE04:B601, cost  2, tag 0, A, 13 Sec
 Dest 2001:DB8:C18:3::/64,
     via FE80::200:5EFF:FE04:B601, cost  2, tag 0, A, 13 Sec

Run the display ripng process-id interface verbose command to view information about the RIPng interface, including whether split horizon and poison reverse are enabled.

<HUAWEI> display ripng 1 interface verbose
 GigabitEthernet1/0/0
    FE80::A0A:200:1
    State : UP, Protocol : RIPNG, MTU : 1440
    Metricin : 0 , Metricout : 1
    Default Route : Disabled
    Poison Reverse : Disabled
    Split Horizon : Enabled           
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Updated: 2019-01-04

Document ID: EDOC1100059437

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