Example for Using XPL to Filter the Routes to Be Received and Advertised (Paragraph-by-Paragraph Editing)

This section provides an example for using XPL to filter the routes to be received and advertised based on sets and route-filters in paragraph editing mode.

Networking Requirements

On the BGP network shown in Figure 1, Device A and Device B belong to AS 100, and Device C, Device D, and Device E belong to AS 200. Device A imports routes 2.2.2.0/24, 3.3.3.0/24, 4.4.4.0/24, and 5.5.5.0/24. The requirements are as follows:
  • Device A advertises routes 2.2.2.0/24, 3.3.3.0/24, and 4.4.4.0/24 to Device B.
  • On receipt of the three routes from Device B, Device C advertises all of them to Device E. On receipt of the three routes from Device B, Device D increases the MED value of the route 2.2.2.0/24 and advertises routes 2.2.2.0/24 and 3.3.3.0/24 to Device E. The MED of the route 2.2.2.0/24 learned from Device C is less than that of the route 2.2.2.0/24 learned from Device D. Therefore, Device E selects Device C as the egress for the traffic destined for 2.2.2.0/24.

To meet the preceding requirements, configure export or import policies. In this example, an export policy is configured on Device A, and two import policies are configured on Device E.

Figure 1 Cyclic figure for filtering the routes to be received and advertised

Device Name

Interface

IP Address

Device A

GE 0/1/16

1.1.5.2/24

Device B

GE 0/1/16

1.1.5.1/24

Device B

GE 0/1/17

1.1.4.2/24

Device B

GE 0/1/18

1.1.3.2/24

Device C

GE 0/1/17

1.1.1.2/24

Device C

GE 0/1/18

1.1.3.1/24

Device D

GE 0/1/17

1.1.2.2/24

Device D

GE 0/1/18

1.1.4.1/24

Device E

GE 0/1/17

1.1.2.1/24

Device E

GE 0/1/18

1.1.1.1/24

Precautions

When using XPL to filter the routes to be received and advertised, note the following points:

  • A prefix range needs to be specified for the IPv4 prefix set as required.

  • IPv4 prefix set names are case-sensitive.

Configuration Roadmap

The configuration roadmap is as follows:

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

  2. Configure four static routes on Device A and import them into BGP.

  3. Configure an export policy on Device A and check the BGP routing table of Device B.

  4. Configure two import policies on Device E and check the BGP routing table of Device E.

Data Preparation

To complete the configuration, you need the following data:

  • Four static routes to be imported by Device A

  • AS 100 (for Device A and Device B) and AS 200 (Device C, Device D, and Device E)

  • Name of an IPv4 prefix set and the routes to be filtered

Procedure

  1. Assign an IP address to each interface. For configuration details, see Configuration Files in this section.
  2. Configure basic BGP functions.

    # Configure Device A.

    <DeviceA> system-view
[~DeviceA] bgp 100
[*DeviceA-bgp] peer 1.1.5.1 as-number 100
[*DeviceA-bgp] commit
[~DeviceA-bgp] quit

    # Configure Device B.

    <DeviceB> system-view
[~DeviceB] bgp 100
[*DeviceB-bgp] peer 1.1.5.2 as-number 100
[*DeviceB-bgp] peer 1.1.3.1 as-number 200
[*DeviceB-bgp] peer 1.1.4.1 as-number 200
[*DeviceB-bgp] commit
[~DeviceB-bgp] quit

    # Configure Device C:

    <DeviceC> system-view
[~DeviceC] bgp 200
[*DeviceC-bgp] peer 1.1.1.1 as-number 200
[*DeviceC-bgp] peer 1.1.3.2 as-number 100
[*DeviceC-bgp] commit
[~DeviceC-bgp] quit

    # Configure Device D:

    <DeviceD> system-view
[~DeviceD] bgp 200
[*DeviceD-bgp] peer 1.1.2.1 as-number 200
[*DeviceD-bgp] peer 1.1.4.2 as-number 100
[*DeviceD-bgp] commit
[~DeviceD-bgp] quit

    # Configure Device E.

    <DeviceE> system-view
[~DeviceE] bgp 200
[*DeviceE-bgp] peer 1.1.1.2 as-number 200
[*DeviceE-bgp] peer 1.1.2.2 as-number 200
[*DeviceE-bgp] commit
[~DeviceE-bgp] quit

  3. Configure four static routes on Device A and import them into BGP.

    [~DeviceA] ip route-static 2.2.2.0 255.255.255.0 NULL0
[*DeviceA] ip route-static 3.3.3.0 255.255.255.0 NULL0
[*DeviceA] ip route-static 4.4.4.0 255.255.255.0 NULL0
[*DeviceA] ip route-static 5.5.5.0 255.255.255.0 NULL0
[*DeviceA] bgp 100
[*DeviceA-bgp] import-route static
[*DeviceA-bgp] commit
[~DeviceA-bgp] quit

    # Check the BGP routing table of Device B. The following command output shows that the four static routes have been added to the BGP routing table of Device B.

    [~DeviceB] display bgp routing-table
 
 BGP Local router ID is 1.1.5.1
 Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
 RPKI validation codes: V - valid, I - invalid, N - not-found


 Total Number of Routes: 4 
        Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i    2.2.2.0/24         1.1.5.2         0          100        0       ?
 *>i    3.3.3.0/24         1.1.5.2         0          100        0       ?
 *>i    4.4.4.0/24         1.1.5.2         0          100        0       ?
 *>i    5.5.5.0/24         1.1.5.2         0          100        0       ?

    # Check the BGP routing table of Device E. The following command output shows that two copies of the four static routes from Device C and Device D have been added to the BGP routing table of Device E.

    [~DeviceE] display bgp routing-table
 
 BGP Local router ID is 1.1.1.1
 Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
 RPKI validation codes: V - valid, I - invalid, N - not-found


 Total Number of Routes: 8 
        Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

   i    2.2.2.0/24         1.1.3.2                    100        0      100?
   i                       1.1.4.2                    100        0      100?
   i    3.3.3.0/24         1.1.4.2                    100        0      100?
   i                       1.1.3.2                    100        0      100?
   i    4.4.4.0/24         1.1.3.2                    100        0      100?
   i                       1.1.4.2                    100        0      100?
   i    5.5.5.0/24         1.1.4.2                    100        0      100?
   i                       1.1.3.2                    100        0      100?

  4. Configure an export policy on Device A.

    # Configure an IPv4 prefix set named prefix1 on Device A.

    [~DeviceA] quit
<DeviceA> edit xpl ip-prefix-list prefix1
xpl ip-prefix-list prefix1
2.2.2.0 24,
3.3.3.0 24,
4.4.4.0 24
end-list

    # Configure a route-filter named r1 on Device A, apply prefix1 to r1, and permit routes 2.2.2.0/24, 3.3.3.0/24, and 4.4.4.0/24.

    <DeviceA> edit xpl route-filter r1
xpl route-filter r1
if ip route-destination in prefix1 then
approve
else
refuse
endif
end-filter

    Press i in the paragraph editing interface view to enter the text editing mode.

    After performing configurations in the text editing mode of the paragraph editing interface view, press Esc to exit from the text editing mode, and press :wq and Enter to save the configurations and exit from the paragraph editing interface view.

    # Configure an export policy on Device A and apply r1 to the policy to filter the routes to be advertised to Device B.

    <DeviceA> system-view
[~DeviceA] bgp 100
[~DeviceA-bgp]  peer 1.1.5.1 route-filter r1 export
[*DeviceA-bgp]  commit
[~DeviceA-bgp]  quit

    # Check the BGP routing table of Device B. The following command output shows that the route 5.5.5.0/24 is not included in the BGP routing table of Device B.

    [~DeviceB] display bgp routing-table
 
 BGP Local router ID is 1.1.5.1
 Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
 RPKI validation codes: V - valid, I - invalid, N - not-found


 Total Number of Routes: 3 
        Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i    2.2.2.0/24         1.1.5.2         0          100        0       ?
 *>i    3.3.3.0/24         1.1.5.2         0          100        0       ?
 *>i    4.4.4.0/24         1.1.5.2         0          100        0       ?

  5. Configure two import policies on Device E.

    # Configure a route-filter named appmed with a pre-defined variable to set the MED.

    [~DeviceE] quit
<DeviceE> edit xpl route-filter appmed
xpl route-filter appmed($med)
apply med $med
end-filter

    # Configure a route-filter named r2 on Device E to permit routes 2.2.2.0/24 and 3.3.3.0/24 and use appmed to set the MED of the route 2.2.2.0/24 to 200.

    <DeviceE> edit xpl route-filter r2
xpl route-filter r2
if ip route-destination in {2.2.2.0 24} then
call route-filter appmed(200)
elseif ip route-destination in {2.2.2.0 24, 3.3.3.0 24} then
approve
else
refuse
endif
end-filter

    # Configure a route-filter named r3 on Device E to set the MED of the route 2.2.2.0/24 to 100.

    <DeviceE> edit xpl route-filter r3
xpl route-filter r3
if ip route-destination in {2.2.2.0 24} then
call route-filter appmed(100)
else
approve
endif
end-filter

    # Configure an import policy on Device E for the routes learned from Device D and apply r2 to the policy. In addition, configure another import policy on Device E for the routes learned from Device C and apply r3 to the policy.

    <DeviceE> system-view
[~DeviceE] bgp 200
[~DeviceE-bgp] peer 1.1.2.2 route-filter r2 import
[*DeviceE-bgp] peer 1.1.1.2 route-filter r3 import
[*DeviceE-bgp] commit
[~DeviceE-bgp] quit

    # Check the BGP routing table of Device E. The following command output shows that the route 4.4.4.0/24 learned from Device D is not included in the BGP routing table of Device B and that the MED values of the routes 2.2.2.0/24 learned from Device C and Device D are 100 and 200, respectively.

    [~DeviceE] display bgp routing-table
 BGP Local router ID is 1.1.1.1
 Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
 RPKI validation codes: V - valid, I - invalid, N - not-found


 Total Number of Routes: 5 
        Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

   i    2.2.2.0/24         1.1.4.2         200        100        0      100?
   i                       1.1.3.2         100        100        0      100?
   i    3.3.3.0/24         1.1.4.2                    100        0      100?
   i                       1.1.3.2                    100        0      100?
   i    4.4.4.0/24         1.1.3.2                    100        0      100?

Configuration Files

  • Device A configuration file

    #
sysname DeviceA
#
interface GigabitEthernet0/1/16
 undo shutdown
 ip address 1.1.5.2 255.255.255.0
#
bgp 100
 peer 1.1.5.1 as-number 100
 #
 ipv4-family unicast
  undo synchronization
  import-route static
  peer 1.1.5.1 enable
  peer 1.1.5.1 route-filter r1 export
#
ip route-static 2.2.2.0 255.255.255.0 NULL0
ip route-static 3.3.3.0 255.255.255.0 NULL0
ip route-static 4.4.4.0 255.255.255.0 NULL0
ip route-static 5.5.5.0 255.255.255.0 NULL0
#
xpl route-filter r1
 if ip route-destination in prefix1 then
  approve
 else
  refuse
 endif
 end-filter
#
xpl ip-prefix-list prefix1
 2.2.2.0 24,
 3.3.3.0 24,
 4.4.4.0 24
 end-list
#
return

  • Device B configuration file

    #
sysname DeviceB
#
interface GigabitEthernet0/1/16
 undo shutdown
 ip address 1.1.5.1 255.255.255.0
#
interface GigabitEthernet0/1/17
 undo shutdown
 ip address 1.1.4.2 255.255.255.0
#
interface GigabitEthernet0/1/18
 undo shutdown
 ip address 1.1.3.2 255.255.255.0
#
bgp 100
 peer 1.1.3.1 as-number 200
 peer 1.1.4.1 as-number 200
 peer 1.1.5.2 as-number 100
 #
 ipv4-family unicast
  undo synchronization
  peer 1.1.3.1 enable
  peer 1.1.4.1 enable
  peer 1.1.5.2 enable
#
return

  • Device C configuration file

    #
sysname DeviceC
#
interface GigabitEthernet0/1/17
 undo shutdown
 ip address 1.1.1.2 255.255.255.0
#
interface GigabitEthernet0/1/18
 undo shutdown
 ip address 1.1.3.1 255.255.255.0
#
bgp 200
 peer 1.1.1.1 as-number 200
 peer 1.1.3.2 as-number 100
 #
 ipv4-family unicast
  undo synchronization
  peer 1.1.1.1 enable
  peer 1.1.3.2 enable
#
return

  • Device D configuration file

    #
sysname DeviceD
#
interface GigabitEthernet0/1/17
 undo shutdown
 ip address 1.1.2.2 255.255.255.0
#
interface GigabitEthernet0/1/18
 undo shutdown
 ip address 1.1.4.1 255.255.255.0
#
bgp 200
 peer 1.1.2.1 as-number 200
 peer 1.1.4.2 as-number 100
 #
 ipv4-family unicast
  undo synchronization
  peer 1.1.2.1 enable
  peer 1.1.4.2 enable
#
return

  • Device E configuration file

    #
sysname DeviceE
#
interface GigabitEthernet0/1/17
 undo shutdown
 ip address 1.1.2.1 255.255.255.0
#
interface GigabitEthernet0/1/18
 undo shutdown
 ip address 1.1.1.1 255.255.255.0
#
bgp 200
 peer 1.1.1.2 as-number 200
 peer 1.1.2.2 as-number 200
 #
 ipv4-family unicast
  undo synchronization
  peer 1.1.1.2 enable
  peer 1.1.1.2 route-filter r3 import
  peer 1.1.2.2 enable
  peer 1.1.2.2 route-filter r2 import
#
xpl route-filter appmed($med)
 apply med $med
 end-filter
#
xpl route-filter r2
 if ip route-destination in {2.2.2.0 24} then
  call route-filter appmed(200)
 elseif ip route-destination in {2.2.2.0 24, 3.3.3.0 24} then
  approve
 else
  refuse
 endif
 end-filter
#
xpl route-filter r3
 if ip route-destination in {2.2.2.0 24} then
  call route-filter appmed(100)
 else
  approve
 endif
 end-filter
#
return
Parent Topic: Configuration Examples for XPL
Copyright © Huawei Technologies Co., Ltd.
Copyright © Huawei Technologies Co., Ltd.
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