Procedure

1. Configure an IP address for each interface.

   # Configure IP addresses for all interfaces of RouterA.

   <Huawei> system-view
   [Huawei] sysname RouterA
   [RouterA] interface gigabitethernet 1/0/0
   [RouterA-GigabitEthernet1/0/0] ip address 9.1.1.1 255.255.255.0
   [RouterA-GigabitEthernet1/0/0] quit
   [RouterA] interface gigabitethernet 2/0/0
   [RouterA-GigabitEthernet2/0/0] ip address 200.1.2.1 255.255.255.0
   [RouterA-GigabitEthernet2/0/0] quit

   The configurations of RouterB and RouterC are similar to the configuration of RouterA, and are not mentioned here.

2. Establish EBGP connections.

   # Configure Router A.

   [RouterA] bgp 10

   [RouterA-bgp] router-id 1.1.1.1

   [RouterA-bgp] peer 200.1.2.2 as-number 20

   [RouterA-bgp] ipv4-family unicast

   [RouterA-bgp-af-ipv4] network 9.1.1.0 255.255.255.0

   [RouterA-bgp-af-ipv4] quit

   [RouterA-bgp] quit

   # Configure Router B.

   [RouterB] bgp 20

   [RouterB-bgp] router-id 2.2.2.2

   [RouterB-bgp] peer 200.1.2.1 as-number 10

   [RouterB-bgp] peer 200.1.3.2 as-number 30

   [RouterB-bgp] quit

   # Configure Router C.

   [RouterC] bgp 30

   [RouterC-bgp] router-id 3.3.3.3 

   [RouterC-bgp] peer 200.1.3.1 as-number 20

   [RouterC-bgp] quit

   # On Router B, view detailed information about route 9.1.1.0/24.

   [RouterB] display bgp routing-table 9.1.1.0

    BGP local router ID : 2.2.2.2
    Local AS number : 20
    Paths:   1 available, 1 best, 1 select
    BGP routing table entry information of 9.1.1.0/24:
    From: 200.1.2.1 (1.1.1.1)
    Route Duration: 00h00m42s
    Direct Out-interface: GigabitEthernet2/0/0
    Original nexthop: 200.1.2.1
    Qos information : 0x0
    AS-path 10, origin igp, MED 0, pref-val 0, valid, external, best, select, active, pre 255
    Advertised to such 2 peers:
       200.1.2.1
       200.1.3.2

   The preceding command output shows that Router B advertises the received BGP route to Router C in AS 30.

   # View the BGP routing table of Router C.

   [RouterC] display bgp routing-table

    BGP Local router ID is 3.3.3.3
    Status codes: * - valid, > - best, d - damped,
                  h - history,  i - internal, s - suppressed, S - Stale
                  Origin : i - IGP, e - EGP, ? - incomplete
   
   
    Total Number of Routes: 1
         Network            NextHop        MED        LocPrf    PrefVal Path/Ogn
   
    *>   9.1.1.0/24         200.1.3.1                             0      20 10i

   The preceding command output shows that Router C has learned route 9.1.1.0/24 from Router B.

3. Configure a BGP community attribute.

   # Configure a routing policy on Router A to prevent BGP routes to be advertised by Router A to Router B from being advertised to any other AS.

   [RouterA] route-policy comm_policy permit node 10

   [RouterA-route-policy] apply community no-export

   [RouterA-route-policy] quit

   # Apply the routing policy.

   [RouterA] bgp 10

   [RouterA-bgp] ipv4-family unicast

   [RouterA-bgp-af-ipv4] peer 200.1.2.2 route-policy comm_policy export

   [RouterA-bgp-af-ipv4] peer 200.1.2.2 advertise-community

   # On Router B, view detailed information about route 9.1.1.0/24.

   [RouterB] display bgp routing-table 9.1.1.0

    BGP local router ID : 2.2.2.2
    Local AS number : 20
    Paths:   1 available, 1 best, 1 select
    BGP routing table entry information of 9.1.1.0/24:
    From: 200.1.2.1 (1.1.1.1)
    Route Duration: 00h00m09s
    Direct Out-interface: GigabitEthernet2/0/0
    Original nexthop: 200.1.2.1
    Qos information : 0x0
    Community:no-export
    AS-path 10, origin igp, MED 0, pref-val 0, valid, external, best, select, active, pre 255
    Not advertised to any peer yet
   

   The preceding command output shows that route 9.1.1.0/24 carries the configured community attribute and Router B does not advertise this route to any other AS.