Configuring BGP AS number substitution

Network requirements

As shown in Figure 59, CE 1 and CE 2 belong to VPN 1 and are connected to PE 1 and PE 2, respectively. The two CEs have the same AS number, 600. Configure BGP AS number substitution on the PEs to enable the CEs to communicate with each other.

Figure 59: Network diagram

Table 16: Interface and IP address assignment

Device

Interface

IP address

Device

Interface

IP address

CE 1

Vlan-int11

10.1.1.1/24

P

Loop0

2.2.2.9/32

Vlan-int12

100.1.1.1/24

Vlan-int11

30.1.1.1/24

PE 1

Loop0

1.1.1.9/32

Vlan-int12

20.1.1.2/24

Vlan-int11

10.1.1.2/24

PE 2

Loop0

3.3.3.9/32

Vlan-int12

20.1.1.1/24

Vlan-int11

30.1.1.2/24

CE 2

Vlan-int12

10.2.1.1/24

Vlan-int12

10.2.1.2/24

Vlan-int13

200.1.1.1/24

Configuration procedure

  1. Configuring basic MPLS L3VPN:

    • Configure OSPF on the MPLS backbone to allow the PEs and P device to learn the routes of the loopback interfaces from each other.

    • Configure basic MPLS and MPLS LDP on the MPLS backbone to establish LDP LSPs.

    • Establish MP-IBGP peer relationship between the PEs to advertise VPNv4 routes.

    • Configure the VPN instance of VPN 1 on PE 2 to allow CE 2 to access the network.

    • Configure the VPN instance of VPN 1 on PE 1 to allow CE 1 to access the network.

    • Configure BGP between PE 1 and CE 1, and between PE 2 and CE 2 and redistribute routes of CEs into PEs.

    For more information about basic MPLS L3VPN configurations, see "Configuring basic MPLS L3VPN."

    # Execute the display ip routing-table command on CE 2. The output shows that CE 2 has learned the route to network 10.1.1.0/24, where the interface used by CE 1 to access PE 1 resides. However, it has not learned the route to the VPN (100.1.1.0/24) behind CE 1.

    <CE2> display ip routing-table
    
    Destinations : 17        Routes : 17
    
    Destination/Mask    Proto  Pre  Cost         NextHop         Interface
    0.0.0.0/32          Direct 0    0            127.0.0.1       InLoop0
    10.1.1.0/24         BGP    255  0            10.2.1.2        Vlan12
    10.2.1.0/24         Direct 0    0            10.2.1.1        Vlan12
    10.2.1.0/32         Direct 0    0            10.2.1.1        Vlan12
    10.2.1.1/32         Direct 0    0            127.0.0.1       InLoop0
    10.2.1.255/32       Direct 0    0            10.2.1.1        Vlan12
    127.0.0.0/8         Direct 0    0            127.0.0.1       InLoop0
    127.0.0.0/32        Direct 0    0            127.0.0.1       InLoop0
    127.0.0.1/32        Direct 0    0            127.0.0.1       InLoop0
    127.255.255.255/32  Direct 0    0            127.0.0.1       InLoop0
    200.1.1.0/24        Direct 0    0            200.1.1.1       Vlan13
    200.1.1.0/32        Direct 0    0            200.1.1.1       Vlan13
    200.1.1.1/32        Direct 0    0            127.0.0.1       InLoop0
    200.1.1.255/24      Direct 0    0            200.1.1.1       Vlan13
    224.0.0.0/4         Direct 0    0            0.0.0.0         NULL0
    224.0.0.0/24        Direct 0    0            0.0.0.0         NULL0
    255.255.255.255/32  Direct 0    0            127.0.0.1       InLoop0
    

    # Execute the display ip routing-table command on CE 1 to verify that CE 1 has not learned the route to the VPN behind CE 2. (Details not shown.)

    # Execute the display ip routing-table vpn-instance command on the PEs. The output shows the route to the VPN behind the peer CE. This example uses PE 2.

    <PE2> display ip routing-table vpn-instance vpn1
    
    Destinations : 15        Routes : 15
    
    Destination/Mask    Proto  Pre  Cost         NextHop         Interface
    0.0.0.0/32          Direct 0    0            127.0.0.1       InLoop0
    10.1.1.0/24         BGP    255  0            1.1.1.9         Vlan11
    10.2.1.0/24         Direct 0    0            10.2.1.2        Vlan12
    10.2.1.0/32         Direct 0    0            10.2.1.2        Vlan12
    10.2.1.2/32         Direct 0    0            127.0.0.1       InLoop0
    10.2.1.255/32       Direct 0    0            10.2.1.2        Vlan12
    100.1.1.0/24        BGP    255  0            1.1.1.9         Vlan11
    127.0.0.0/8         Direct 0    0            127.0.0.1       InLoop0
    127.0.0.0/32        Direct 0    0            127.0.0.1       InLoop0
    127.0.0.1/32        Direct 0    0            127.0.0.1       InLoop0
    127.255.255.255/32  Direct 0    0            127.0.0.1       InLoop0
    200.1.1.0/24        BGP    255  0            10.2.1.1        Vlan12
    224.0.0.0/4         Direct 0    0            0.0.0.0         NULL0
    224.0.0.0/24        Direct 0    0            0.0.0.0         NULL0
    255.255.255.255/32  Direct 0    0            127.0.0.1       InLoop0
    

    # Enable BGP update packet debugging on PE 2. The output shows that PE 2 advertises the route to 100.1.1.1/32, and the AS_PATH is 100 600.

    <PE2> terminal monitor
    <PE2> terminal logging level 7
    <PE2> debugging bgp update vpn-instance vpn1 10.2.1.1 ipv4
    <PE2> refresh bgp all export ipv4 vpn-instance vpn1
    *Jun 13 16:12:52:096 2012 PE2 BGP/7/DEBUG: -MDC=1;
             BGP.vpn1: Send UPDATE to peer 10.2.1.1 for following destinations:
             Origin       : Incomplete
             AS Path      : 100 600
             Next Hop     : 10.2.1.2
             100.1.1.0/24,
    

    # Execute the display bgp routing-table ipv4 peer received-routes command on CE 2. The output shows that CE 2 has not received the route to 100.1.1.0/24.

    <CE2> display bgp routing-table ipv4 peer 10.2.1.2 received-routes
    
     Total number of routes: 2
    
     BGP local router ID is 200.1.1.1
     Status codes: * - valid, > - best, d - dampened, h - history,
                   s - suppressed, S - stale, i - internal, e - external
                   Origin: i - IGP, e - EGP, ? - incomplete
    
         Network            NextHop         MED        LocPrf     PrefVal Path/Ogn
    
    * >e 10.1.1.0/24        10.2.1.2                              0       100?
    *  e 10.2.1.0/24        10.2.1.2        0                     0       100?
    
  2. Configure BGP AS number substitution on PE 2.

    <PE2> system-view
    [PE2] bgp 100
    [PE2-bgp] ip vpn-instance vpn1
    [PE2-bgp-vpn1] peer 10.2.1.1 substitute-as
    [PE2-bgp-vpn1] address-family ipv4 unicast
    [PE2-bgp-ipv4-vpn1] peer 10.2.1.1 enable
    [PE2-bgp-ipv4-vpn1] quit
    [PE2-bgp-vpn1] quit
    [PE2-bgp] quit
    

Verifying the configuration

# The output shows that among the routes advertised by PE 2 to CE 2, the AS_PATH of 100.1.1.0/24 has changed from 100 600 to 100 100.

*Jun 13 16:15:59:456 2012 PE2 BGP/7/DEBUG: -MDC=1;
         BGP.vpn1: Send UPDATE to peer 10.2.1.1 for following destinations:
         Origin       : Incomplete
         AS Path      : 100 100
         Next Hop     : 10.2.1.2
         100.1.1.0/24,

# Display again the routing information that CE 2 has received and the routing table.

<CE2> display bgp routing-table ipv4 peer 10.2.1.2 received-routes

 Total number of routes: 3

 BGP local router ID is 200.1.1.1
 Status codes: * - valid, > - best, d - dampened, h - history,
               s - suppressed, S - stale, i - internal, e - external
               Origin: i - IGP, e - EGP, ? - incomplete

     Network            NextHop         MED        LocPrf     PrefVal Path/Ogn

* >e 10.1.1.0/24        10.2.1.2                              0       100?
*  e 10.2.1.0/24        10.2.1.2        0                     0       100?
* >e 100.1.1.0/24       10.2.1.2                              0       100 100?
<CE2> display ip routing-table

Destinations : 18        Routes : 18

Destination/Mask    Proto  Pre  Cost         NextHop         Interface
0.0.0.0/32          Direct 0    0            127.0.0.1       InLoop0
10.1.1.0/24         BGP    255  0            10.2.1.2        Vlan12
10.2.1.0/24         Direct 0    0            10.2.1.1        Vlan12
10.2.1.0/32         Direct 0    0            10.2.1.1        Vlan12
10.2.1.1/32         Direct 0    0            127.0.0.1       InLoop0
10.2.1.255/32       Direct 0    0            10.2.1.1        Vlan12
100.1.1.0/24        BGP    255  0            10.2.1.2        Vlan12
127.0.0.0/8         Direct 0    0            127.0.0.1       InLoop0
127.0.0.0/32        Direct 0    0            127.0.0.1       InLoop0
127.0.0.1/32        Direct 0    0            127.0.0.1       InLoop0
127.255.255.255/32  Direct 0    0            127.0.0.1       InLoop0
200.1.1.0/24        Direct 0    0            200.1.1.1       Vlan13
200.1.1.0/32        Direct 0    0            200.1.1.1       Vlan13
200.1.1.1/32        Direct 0    0            127.0.0.1       InLoop0
200.1.1.255/32      Direct 0    0            200.1.1.1       Vlan13
224.0.0.0/4         Direct 0    0            0.0.0.0         NULL0
224.0.0.0/24        Direct 0    0            0.0.0.0         NULL0
255.255.255.255/32  Direct 0    0            127.0.0.1       InLoop0

# Verify that the VLAN interfaces of CE 1 and CE 2 can ping each other. (Details not shown.)