Example for Configuring Routing Loop Detection for Routes Imported from OSPF to IS-IS

This section provides an example for configuring routing loop detection for routes imported from OSPF to IS-IS.

Networking Requirements

On the live network, IS-IS routes can be imported to an OSPF process for redistribution. In such a scenario, routing policies are usually configured on multiple devices to prevent routing loops. If routing policies are incorrectly configured on the devices that import routes, routing loops may occur. To prevent this problem, configure routing loop detection for the routes imported to IS-IS.

On the network shown in Example for Configuring Routing Loop Detection for Routes Imported from OSPF to IS-IS, IS-IS process 2 is configured on DeviceA, DeviceB, and DeviceF, an OSPF process is configured on DeviceB, DeviceC, DeviceE, and DeviceF, and IS-IS process 1 is configured on DeviceC, DeviceD, and DeviceE. DeviceC is configured to import routes from IS-IS process 1 to the OSPF process, DeviceB is configured to import routes from the OSPF process to IS-IS process 2, and DeviceF is configured to import routes from IS-IS process 2 to the OSPF process.

Figure 1 Routing loop detection for routes imported from OSPF to IS-IS

In this example, interface1, interface2, and interface3 represent GE0/1/0, GE0/1/8, and GE0/1/16, respectively.


Configuration Roadmap

The configuration roadmap is as follows:

  1. Disable routing loop detection, which is enabled by default.

  2. Configure IP addresses for interfaces on each device to implement area connectivity.

  3. Enable IS-IS and OSPF, and configure basic IS-IS and OSPF functions.

  4. Configure route import to construct a routing loop.

  5. View routing entries to check whether a routing loop occurs.

  6. Enable routing loop detection and view routing entries to check whether the routing loop is eliminated.

Procedure

  1. Disable routing loop detection (enabled by default) on each device.

    # Disable routing loop detection. DeviceA is used as an example.

    <DeviceA> system-view
[~DeviceA] route loop-detect isis disable
[*DeviceA] route loop-detect ospf disable
[*DeviceA] commit

    The configurations of other devices are similar to those of DeviceA. For configuration details, see Configuration Files in this section.

  2. Configure an IP address for each interface.

    DeviceA, DeviceB, DeviceC, and DeviceD are used as examples.

    # Configure DeviceA.

    <DeviceA> system-view
[~DeviceA] interface gigabitethernet 0/1/0
[*DeviceA-GigabitEthernet0/1/0] ip address 10.12.1.1 24
[*DeviceA-GigabitEthernet0/1/0] quit
[*DeviceA] interface gigabitethernet 0/1/8
[*DeviceA-GigabitEthernet0/1/8] ip address 10.16.1.1 24
[*DeviceA-GigabitEthernet0/1/8] quit
[*DeviceA] commit

    # Configure DeviceB.

    <DeviceB> system-view
[~DeviceB] interface gigabitethernet 0/1/0
[*DeviceB-GigabitEthernet0/1/0] ip address 10.12.1.2 24
[*DeviceB-GigabitEthernet0/1/0] quit
[*DeviceB] interface gigabitethernet 0/1/8
[*DeviceB-GigabitEthernet0/1/8] ip address 10.26.1.2 24
[*DeviceB-GigabitEthernet0/1/8] quit
[*DeviceB] interface gigabitethernet 0/1/16
[*DeviceB-GigabitEthernet0/1/16] ip address 10.23.1.2 24
[*DeviceB-GigabitEthernet0/1/16] quit
[*DeviceB] commit

    # Configure DeviceC.

    <DeviceC> system-view
[~DeviceC] interface gigabitethernet 0/1/0
[*DeviceC-GigabitEthernet0/1/0] ip address 10.23.1.3 24
[*DeviceC-GigabitEthernet0/1/0] quit
[*DeviceC] interface gigabitethernet 0/1/8
[*DeviceC-GigabitEthernet0/1/8] ip address 10.35.1.3 24
[*DeviceC-GigabitEthernet0/1/8] quit
[*DeviceC] interface gigabitethernet 0/1/16
[*DeviceC-GigabitEthernet0/1/16] ip address 10.34.1.3 24
[*DeviceC-GigabitEthernet0/1/16] quit
[*DeviceC] commit

    # Configure DeviceD. The route 10.1.1.1/32 on the loopback interface of DeviceD is used as the locally originated route.

    <DeviceD> system-view
[~DeviceD] interface loopBack 1
[*DeviceD-LoopBack1] ip address 10.1.1.1 32
[*DeviceD-LoopBack1] quit
[*DeviceD-LoopBack1] commit

    The configurations of other devices are similar to those of the preceding devices. For details, see Configuration Files in this section.

  3. Enable IS-IS and OSPF, and configure basic IS-IS and OSPF functions and a link cost to implement intra-area interworking.

    # Configure IS-IS process 2 on DeviceA, DeviceB, and DeviceF. DeviceA is used as an example.

    [~DeviceA] isis 2
[*DeviceA-isis-2] cost-style wide
[*DeviceA-isis-2] network-entity 10.1111.0000.0001.00
[*DeviceA-isis-2] quit
[*DeviceA] interface gigabitethernet 0/1/0
[*DeviceA-GigabitEthernet0/1/0] isis enable 2
[*DeviceA-GigabitEthernet0/1/0] isis circuit-type p2p
[*DeviceA-GigabitEthernet0/1/0] isis cost 10
[*DeviceA-GigabitEthernet0/1/0] quit
[*DeviceA] interface gigabitethernet 0/1/8
[*DeviceA-GigabitEthernet0/1/8] isis enable 2
[*DeviceA-GigabitEthernet0/1/8] isis circuit-type p2p
[*DeviceA-GigabitEthernet0/1/8] isis cost 10
[*DeviceA-GigabitEthernet0/1/8] quit
[*DeviceA] commit

    The configurations of DeviceB and DeviceF are similar to those of DeviceA. For configuration details, see Configuration Files in this section.

    # Configure IS-IS process 1 on DeviceC, DeviceD, and DeviceE. DeviceD is used as an example.

    [~DeviceD] isis 1
[*DeviceD-isis-1] cost-style wide
[*DeviceD-isis-1] network-entity 10.4444.0000.0001.00
[*DeviceD-isis-1] quit
[*DeviceD] interface gigabitethernet 0/1/0
[*DeviceD-GigabitEthernet0/1/0] isis enable 1
[*DeviceD-GigabitEthernet0/1/0] isis circuit-type p2p
[*DeviceD-GigabitEthernet0/1/0] isis cost 10
[*DeviceD-GigabitEthernet0/1/0] quit
[*DeviceD] interface gigabitethernet 0/1/8
[*DeviceD-GigabitEthernet0/1/8] isis enable 1
[*DeviceD-GigabitEthernet0/1/8] isis circuit-type p2p
[*DeviceD-GigabitEthernet0/1/8] isis cost 10
[*DeviceD-GigabitEthernet0/1/8] quit
[*DeviceD] commit

    The configurations of DeviceC and DeviceE are similar to those of DeviceD. For configuration details, see Configuration Files in this section.

    # Configure OSPF on DeviceB, DeviceC, DeviceE, and DeviceF. DeviceB is used as an example.

    [~DeviceB] ospf 1 router-id 2.2.2.2
[*DeviceB-ospf-1] area 0
[*DeviceB-ospf-1-area-0.0.0.0] network 10.23.1.0 0.0.0.255
[*DeviceB-ospf-1-area-0.0.0.0] network 10.26.1.0 0.0.0.255
[*DeviceB-ospf-1-area-0.0.0.0] quit
[*DeviceB] interface gigabitethernet 0/1/0
[*DeviceB-GigabitEthernet0/1/0] ospf enable 1 area 0.0.0.0
[*DeviceB-GigabitEthernet0/1/0] quit
[*DeviceB] interface gigabitethernet 0/1/8
[*DeviceB-GigabitEthernet0/1/8] ospf enable 1 area 0.0.0.0
[*DeviceB-GigabitEthernet0/1/8] quit
[*DeviceB] commit

    The configurations of DeviceC, DeviceD, and DeviceE are similar to those of DeviceB. For configuration details, see Configuration Files in this section.

  4. Configure route import.

    # Configure DeviceC to import routes from IS-IS process 1 to the OSPF process.

    [~DeviceC] ospf 1 router-id 3.3.3.3
[*DeviceC-ospf-1] import-route isis 1 cost 100 type 2
[*DeviceC-ospf-1] commit

    # Configure DeviceB to import routes from the OSPF process to IS-IS process 2.

    [~DeviceB] isis 2
[*DeviceB-isis-2] import-route ospf 1
[*DeviceB-ospf-1] commit

    # Configure DeviceF to import routes from IS-IS process 2 to the OSPF process.

    [~DeviceF] ospf 1 router-id 6.6.6.6
[*DeviceF-ospf-1] import-route isis 2 cost 10 type 2
[*DeviceF-ospf-1] commit

  5. View the routing tables on DeviceB, DeviceE, and DeviceF to check whether a routing loop occurs.

    # Check OSPF neighbor information on DeviceB.

    [~DeviceB] display ospf peer
(M) Indicates MADJ neighbor


          OSPF Process 1 with Router ID 2.2.2.2
                Neighbors

 Area 0.0.0.0 interface 10.23.1.2 (GigabitEthernet0/1/16)'s neighbors
 Router ID: 3.3.3.3              Address: 10.23.1.3
   State: Full           Mode:Nbr is Master     Priority: 1
   DR: 10.23.1.3        BDR: 10.23.1.2        MTU: 0
   Dead timer due in  3  sec
   Retrans timer interval: 5
   Neighbor is up for 28h43m46s
   Neighbor Up Time : 2021-08-23 09:20:09
   Authentication Sequence: [ 0 ]

 Area 0.0.0.0 interface 10.26.1.2 (GigabitEthernet0/1/8)'s neighbors
 Router ID: 6.6.6.6              Address: 10.26.1.6
   State: Full           Mode:Nbr is Master     Priority: 1
   DR: None              BDR: None              MTU: 0
   Dead timer due in  4  sec
   Retrans timer interval: 5
   Neighbor is up for 28h43m46s
   Neighbor Up Time : 2021-08-23 09:20:09
   Authentication Sequence: [ 0 ]

    # Check IS-IS neighbor information on DeviceB.

    [~DeviceB] display isis peer
                          Peer information for ISIS(2)

  System Id      Interface          Circuit Id        State HoldTime Type     PRI
--------------------------------------------------------------------------------
6666.0000.0001  GE0/1/16           0000000011         Up   29s      L1L2     --
1111.0000.0001  GE0/1/8           0000000025         Up   27s      L1L2     --

Total Peer(s): 2

    The preceding command outputs show that DeviceB has established connections with DeviceA, DeviceC, and DeviceF.

    # Check the routing table on DeviceB.

    [~DeviceB] display ip routing 10.1.1.1
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table : _public_
Summary Count : 1

Destination/Mask    Proto   Pre  Cost        Flags NextHop         Interface

        10.1.1.1/24  O_ASE   150  1             D   10.26.1.6      GigabitEthernet0/1/16

    The preceding command output shows that the next hop of the route displayed on DeviceB is DeviceF.

    # Check OSPF neighbor information on DeviceF.

    [~DeviceF] display ospf peer
(M) Indicates MADJ neighbor


          OSPF Process 1 with Router ID 6.6.6.6
                Neighbors

 Area 0.0.0.0 interface 10.56.1.6 (GigabitEthernet0/1/16)'s neighbors
 Router ID: 5.5.5.5              Address: 10.56.1.5
   State: Full           Mode:Nbr is Slave      Priority: 1
   DR: 10.56.1.6        BDR: 10.56.1.5        MTU: 0
   Dead timer due in  4  sec
   Retrans timer interval: 5
   Neighbor is up for 28h52m49s
   Neighbor Up Time : 2021-08-23 09:20:11
   Authentication Sequence: [ 0 ]

 Area 0.0.0.0 interface 10.26.1.6 (GigabitEthernet0/1/8)'s neighbors
 Router ID: 2.2.2.2              Address: 10.26.1.2
   State: Full           Mode:Nbr is Slave      Priority: 1
   DR: None              BDR: None              MTU: 0
   Dead timer due in  3  sec
   Retrans timer interval: 5
   Neighbor is up for 28h52m51s
   Neighbor Up Time : 2021-08-23 09:20:09
   Authentication Sequence: [ 0 ]

    # Check IS-IS neighbor information on DeviceF.

    [~DeviceF] display isis peer
                          Peer information for ISIS(2)

  System Id       Interface          Circuit Id        State HoldTime Type     PRI
--------------------------------------------------------------------------------
2222.0000.0001  GE0/1/8           0000000011         Up   28s      L1L2     --
1111.0000.0001  GE0/1/0           0000000011         Up   25s      L1L2     --

Total Peer(s): 2

    The preceding command outputs show that DeviceF has established connections with DeviceA, DeviceB, and DeviceE.

    # Check the routing table on DeviceF.

    [~DeviceF] display ip routing 10.1.1.1
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table : _public_
Summary Count : 1

Destination/Mask    Proto   Pre  Cost        Flags NextHop         Interface

        10.1.1.1/24  ISIS-L2 15   10            D   10.26.1.2      GigabitEthernet0/1/8

    The preceding command output shows that the next hop of the route displayed on DeviceF is DeviceB.

    In this case, a routing loop is formed between DeviceB and DeviceF.

  6. Enable routing loop detection on each device.

    # Configure DeviceA, which is used as an example.

    [~DeviceA] undo route loop-detect isis disable
[*DeviceA] undo route loop-detect ospf disable
[*DeviceA] commit

    The configurations of other devices are similar to those of DeviceA. For configuration details, see Configuration Files in this section.

  7. Check whether the routing loop is eliminated.

    # Check the routing table on DeviceB.

    [~DeviceB] display ip routing 10.1.1.1
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table : _public_
Summary Count : 1

Destination/Mask    Proto   Pre  Cost        Flags NextHop         Interface

        10.1.1.1/24  O_ASE   150  100           D   10.23.1.3       GigabitEthernet0/1/16

    The preceding command output shows that the next hop of the route displayed on DeviceB is DeviceC.

    # Check the routing table on DeviceF.

    [~DeviceF] display ip routing 10.1.1.1
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table : _public_
Summary Count : 1

Destination/Mask    Proto   Pre  Cost        Flags NextHop         Interface

        10.1.1.1/24  ISIS-L2 15   10            D   10.26.1.2       GigabitEthernet0/1/8

    The preceding command output shows that the next hop of the route displayed on DeviceF is DeviceB and that DeviceB no longer prefers the route received from DeviceF. This means that the routing loop between DeviceB and DeviceF is eliminated.

Configuration Files

  • DeviceA configuration file

    #
sysname DeviceA
#
isis 2
 cost-style wide
 network-entity 10.1111.0000.0001.00
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 10.12.1.1 255.255.255.0
 isis enable 2
 isis circuit-type p2p
 isis cost 10
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 10.16.1.1 255.255.255.0
 isis enable 2
 isis circuit-type p2p
 isis cost 10
#
return

  • DeviceB configuration file

    #
sysname DeviceB
#
isis 2
 cost-style wide
 network-entity 10.2222.0000.0001.00
 import-route ospf 1 
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 10.12.1.2 255.255.255.0
 isis enable 2
 isis circuit-type p2p
 isis cost 10
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 10.26.1.2 255.255.255.0
 ospf network-type p2p
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
 isis enable 2
 isis circuit-type p2p
 isis cost 10
#
interface GigabitEthernet0/1/16
 undo shutdown
 ip address 10.23.1.2 255.255.255.0
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
#
ospf 1 router-id 2.2.2.2
 opaque-capability enable 
 area 0.0.0.0
#
return

  • DeviceC configuration file

    #
sysname DeviceC
#
isis 1
 cost-style wide
 network-entity 10.3333.0000.0001.00
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 10.23.1.3 255.255.255.0
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 10.35.1.3 255.255.255.0
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
 isis enable 1
 isis circuit-type p2p
 isis cost 10
#
interface GigabitEthernet0/1/16
 undo shutdown
 ip address 10.34.1.3 255.255.255.0
 isis enable 1
 isis circuit-type p2p
 isis cost 10
#
ospf 1 router-id 3.3.3.3
 import-route isis 1 cost 100 type 2
 opaque-capability enable 
 area 0.0.0.0
#
return

  • DeviceD configuration file

    #
sysname DeviceD
#
isis 1
 cost-style wide
 network-entity 10.4444.0000.0001.00
#
interface LoopBack1
 ip address 10.1.1.1 255.255.255.255
 isis enable 1
 isis cost 10
#
return

  • DeviceE configuration file

    #
sysname DeviceE
#
isis 1
 cost-style wide
 network-entity 10.5555.0000.0001.00
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 10.56.1.5 255.255.255.0
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 10.35.1.5 255.255.255.0
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
 isis enable 1
 isis circuit-type p2p
 isis cost 10
#
interface GigabitEthernet0/1/16
 undo shutdown
 ip address 10.45.1.5 255.255.255.0
 isis enable 1
 isis circuit-type p2p
 isis cost 10
#
ospf 1 router-id 5.5.5.5
 import-route isis 1 cost 100 type 2
 opaque-capability enable 
 area 0.0.0.0
#
return

  • DeviceF configuration file

    #
sysname DeviceF
#
isis 2
 cost-style wide
 network-entity 10.6666.0000.0001.00
 #
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 10.16.1.6 255.255.255.0
 isis enable 2
 isis circuit-type p2p
 isis cost 10
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 10.26.1.6 255.255.255.0
 ospf network-type p2p
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
 isis enable 2
 isis circuit-type p2p
 isis cost 10
#
interface GigabitEthernet0/1/16
 undo shutdown
 ip address 10.56.1.6 255.255.255.0
 ospf timer hello 1
 ospf enable 1 area 0.0.0.0
#
ospf 1 router-id 6.6.6.6
 import-route isis 2 cost 10 type 2
 opaque-capability enable
 area 0.0.0.0
#
return
Parent Topic: IS-IS Configuration Examples
Copyright © Huawei Technologies Co., Ltd.
Copyright © Huawei Technologies Co., Ltd.
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