Example for Filtering the Received Routes and Those to Be Advertised

Filters can be applied to the received routes and those to be advertised based on networking requirements.

Networking Requirements

In Figure 1, on the network running OSPF, Device A receives routes from the Internet and provides some Internet routes for Device B. It is required that Device A provide only 172.16.17.0/24, 172.16.18.0/24, and 172.16.19.0/24 for Device B, Device C receive only 172.16.18.0/24, and that Device D receive all the routes provided by Device B.

Figure 1 Filtering the received routes and those to be advertised

Interfaces 1 through 3 in this example represent GE 0/1/0, GE 0/1/8, and GE 0/1/16, respectively.


Precautions

When filtering received routes and those to be advertised, note the following rules:

  • When configuring an IP prefix list, specify the IP prefix range as required.

  • The IP prefix list name is case sensitive.

Configuration Roadmap

The configuration roadmap is as follows:

  1. Configure basic OSPF functions on Device A, Device B, Device C, and Device D.

  2. Configure static routes on Device A and import these routes into OSPF.

  3. Configure a policy to filter routes to be advertised on Device A and then check the routing table on Device B.

  4. Configure a policy to filter received routes on Device C and then check the routing table on Device C.

Data Preparation

To complete the configuration, you need the following data:

  • Five static routes imported by Device A

  • Area 0 (backbone area), in which Device A, Device B, Device C, and Device D are located

  • Name of the IP prefix list and routes to be filtered

Procedure

  1. Configure IP addresses for interfaces. For configuration details, see Configuration Files in this section.
  2. Configure OSPF.

    # Configure Device A.

    [~DeviceA] ospf
[*DeviceA-ospf-1] area 0
[*DeviceA-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
[*DeviceA-ospf-1-area-0.0.0.0] commit
[~DeviceA-ospf-1-area-0.0.0.0] quit
[~DeviceA-ospf-1] quit

    # Configure Device B.

    [~DeviceB] ospf
[*DeviceB-ospf-1] area 0
[*DeviceB-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
[*DeviceB-ospf-1-area-0.0.0.0] network 192.168.2.0 0.0.0.255
[*DeviceB-ospf-1-area-0.0.0.0] network 192.168.3.0 0.0.0.255
[*DeviceB-ospf-1-area-0.0.0.0] commit
[~DeviceB-ospf-1-area-0.0.0.0] quit

    # Configure Device C.

    [~DeviceC] ospf
[*DeviceC-ospf-1] area 0
[*DeviceC-ospf-1-area-0.0.0.0] network 192.168.2.0 0.0.0.255
[*DeviceC-ospf-1-area-0.0.0.0] commit
[~DeviceC-ospf-1-area-0.0.0.0] quit
[~DeviceC-ospf-1] quit

    # Configure Device D.

    [~DeviceD] ospf
[*DeviceD-ospf-1] area 0
[*DeviceD-ospf-1-area-0.0.0.0] network 192.168.3.0 0.0.0.255
[*DeviceD-ospf-1-area-0.0.0.0] commit
[~DeviceD-ospf-1-area-0.0.0.0] quit

  3. Configure five static routes on Device A, and import these routes into OSPF.

    [~DeviceA] ip route-static 172.16.16.0 24 NULL0
[*DeviceA] ip route-static 172.16.17.0 24 NULL0
[*DeviceA] ip route-static 172.16.18.0 24 NULL0
[*DeviceA] ip route-static 172.16.19.0 24 NULL0
[*DeviceA] ip route-static 172.16.20.0 24 NULL0
[*DeviceA] ospf
[*DeviceA-ospf-1] import-route static
[*DeviceA-ospf-1] commit
[~DeviceA-ospf-1] quit

    # Display the IP routing table on Device B. The following command output shows that the five static routes have been imported into OSPF.

    [~DeviceB] display ip routing-table
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table : Public
         Destinations : 22       Routes : 22

Destination/Mask    Proto  Pre  Cost        Flags NextHop         Interface

        1.1.1.1/32  Direct 0    0             D  127.0.0.1       LoopBack1
      127.0.0.0/8   Direct 0    0             D  127.0.0.1       InLoopBack0
      127.0.0.1/32  Direct 0    0             D  127.0.0.1       InLoopBack0
127.255.255.255/32  Direct 0    0             D  127.0.0.1       InLoopBack0
255.255.255.255/32  Direct 0    0             D  127.0.0.1       InLoopBack0
   172.16.16.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
   172.16.17.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
   172.16.18.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
   172.16.19.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
   172.16.20.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
    192.168.1.0/24  Direct 0    0             D  192.168.1.2     GigabitEthernet0/1/0
    192.168.1.1/32  Direct 0    0             D  192.168.1.1     GigabitEthernet0/1/0
    192.168.1.2/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/0
  192.168.1.255/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/0
    192.168.2.0/24  Direct 0    0             D  192.168.2.1     GigabitEthernet0/1/16
    192.168.2.1/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/16
    192.168.2.2/32  Direct 0    0             D  192.168.2.2     GigabitEthernet0/1/16
  192.168.2.255/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/16
    192.168.3.0/24  Direct 0    0             D  192.168.3.1     GigabitEthernet0/1/8
    192.168.3.1/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/8
    192.168.3.2/32  Direct 0    0             D  192.168.3.2     GigabitEthernet0/1/8
  192.168.3.255/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/8

  4. Configure a policy to filter routes to be advertised.

    # Configure the IP prefix list named a2b on Device A.

    [~DeviceA] ip ip-prefix a2b index 10 permit 172.16.17.0 24
[*DeviceA] ip ip-prefix a2b index 20 permit 172.16.18.0 24
[*DeviceA] ip ip-prefix a2b index 30 permit 172.16.19.0 24
[*DeviceA] commit

    # Configure a policy on Device A and use the IP prefix list named a2b to filter routes.

    [~DeviceA] ospf
[*DeviceA-ospf-1] filter-policy ip-prefix a2b export static
[*DeviceA-ospf-1] commit
[~DeviceA-ospf-1] quit

    # Display the IP routing table on Device B. The following command output shows that Device B has received only three routes specified in the IP prefix list named a2b.

    [~DeviceB] display ip routing-table
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table : Public
         Destinations : 20       Routes : 20

Destination/Mask    Proto  Pre  Cost        Flags NextHop         Interface

        1.1.1.1/32  Direct 0    0             D  127.0.0.1       LoopBack1
      127.0.0.0/8   Direct 0    0             D  127.0.0.1       InLoopBack0
      127.0.0.1/32  Direct 0    0             D  127.0.0.1       InLoopBack0
127.255.255.255/32  Direct 0    0             D  127.0.0.1       InLoopBack0
255.255.255.255/32  Direct 0    0             D  127.0.0.1       InLoopBack0
   172.16.17.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
   172.16.18.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
   172.16.19.0/24  O_ASE  150  1             D  192.168.1.1     GigabitEthernet0/1/0
    192.168.1.0/24  Direct 0    0             D  192.168.1.2     GigabitEthernet0/1/0
    192.168.1.1/32  Direct 0    0             D  192.168.1.1     GigabitEthernet0/1/0
    192.168.1.2/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/0
  192.168.1.255/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/0
    192.168.2.0/24  Direct 0    0             D  192.168.2.1     GigabitEthernet0/1/16
    192.168.2.1/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/16
    192.168.2.2/32  Direct 0    0             D  192.168.2.2     GigabitEthernet0/1/16
  192.168.2.255/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/16
    192.168.3.0/24  Direct 0    0             D  192.168.3.1     GigabitEthernet0/1/8
    192.168.3.1/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/8
    192.168.3.2/32  Direct 0    0             D  192.168.3.2     GigabitEthernet0/1/8
  192.168.3.255/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/8

  5. Configure a policy to filter received routes.

    # Configure the IP prefix list named in on Device C.

    [~DeviceC] ip ip-prefix in index 10 permit 172.16.18.0 24
[*DeviceC] commit

    # Configure a policy on Device C and use the IP prefix list named in to filter routes.

    [~DeviceC] ospf
[*DeviceC-ospf-1] filter-policy ip-prefix in import
[*DeviceC-ospf-1] commit

    # Display the IP routing table on Device C. The following command output shows that Device C has received only one route specified in the IP prefix list named in.

    [~DeviceC] display ip routing-table
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table : Public
         Destinations : 12       Routes : 12

Destination/Mask    Proto  Pre  Cost        Flags NextHop         Interface

        1.1.1.1/32  O_ASE  10   1             D  192.168.2.1     GigabitEthernet0/1/0
      127.0.0.0/8   Direct 0    0             D  127.0.0.1       InLoopBack0
      127.0.0.1/32  Direct 0    0             D  127.0.0.1       InLoopBack0
127.255.255.255/32  Direct 0    0             D  127.0.0.1       InLoopBack0
255.255.255.255/32  Direct 0    0             D  127.0.0.1       InLoopBack0
   172.16.18.0/24  O_ASE  150  1             D  192.168.2.1     GigabitEthernet0/1/0
    192.168.1.0/24  O_ASE  10   2             D  192.168.2.1     GigabitEthernet0/1/0
    192.168.2.0/24  Direct 0    0             D  192.168.2.2     GigabitEthernet0/1/0
    192.168.2.1/32  Direct 0    0             D  192.168.2.1     GigabitEthernet0/1/0
    192.168.2.2/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/0
  192.168.2.255/32  Direct 0    0             D  127.0.0.1       GigabitEthernet0/1/0
    192.168.3.0/24  O_ASE  10   2             D  192.168.2.1     GigabitEthernet0/1/0

Configuration Files

  • Device A configuration file

    #
sysname DeviceA
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 192.168.1.1 255.255.255.0
#
ospf 1
 filter-policy ip-prefix a2b export static
 import-route static
 area 0.0.0.0
  network 192.168.1.0 0.0.0.255
#
ip ip-prefix a2b index 10 permit 172.16.17.0 24
ip ip-prefix a2b index 20 permit 172.16.18.0 24
ip ip-prefix a2b index 30 permit 172.16.19.0 24
#
ip route-static 172.16.16.0 255.255.255.0 NULL0
ip route-static 172.16.17.0 255.255.255.0 NULL0
ip route-static 172.16.18.0 255.255.255.0 NULL0
ip route-static 172.16.19.0 255.255.255.0 NULL0
ip route-static 172.16.20.0 255.255.255.0 NULL0
#
return

  • Device B configuration file

    #
sysname DeviceB
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 192.168.1.2 255.255.255.0
#
interface GigabitEthernet0/1/8
 undo shutdown
 ip address 192.168.3.1 255.255.255.0
#
interface GigabitEthernet0/1/16
 undo shutdown
 ip address 192.168.2.1 255.255.255.0
#
ospf 1
 area 0.0.0.0
  network 192.168.1.0 0.0.0.255
  network 192.168.2.0 0.0.0.255
  network 192.168.3.0 0.0.0.255
#
return

  • Device C configuration file

    #
sysname DeviceC
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 192.168.2.2 255.255.255.0
#
ospf 1
 filter-policy ip-prefix in import
 area 0.0.0.0
  network 192.168.2.0 0.0.0.255
#
ip ip-prefix in index 10 permit 172.16.18.0 24
#
return

  • Device D configuration file

    #
sysname DeviceD
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 192.168.3.2 255.255.255.0
#
ospf 1
 area 0.0.0.0
  network 192.168.3.0 0.0.0.255
#
return
Parent Topic: Configuration Examples for Routing Policies
Copyright © Huawei Technologies Co., Ltd.
Copyright © Huawei Technologies Co., Ltd.
Next topic >