Example for Configuring MED Attributes to Control BGP Route Selection

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 200.1.1.2 255.255.255.0
   [RouterA-GigabitEthernet1/0/0] quit
   [RouterA] interface gigabitethernet 2/0/0
   [RouterA-GigabitEthernet2/0/0] ip address 200.1.2.2 255.255.255.0
   [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 BGP connections.

   # Configure Router A.

   [RouterA] bgp 65008

   [RouterA-bgp] router-id 1.1.1.1

   [RouterA-bgp] peer 200.1.1.1 as-number 65009

   [RouterA-bgp] peer 200.1.2.1 as-number 65009

   [RouterA-bgp] quit

   # Configure Router B.

   [RouterB] bgp 65009

   [RouterB-bgp] router-id 2.2.2.2

   [RouterB-bgp] peer 200.1.1.2 as-number 65008

   [RouterB-bgp] peer 9.1.1.2 as-number 65009

   [RouterB-bgp] ipv4-family unicast

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

   [RouterB-bgp-af-ipv4] quit

   [RouterB-bgp] quit

   # Configure Router C.

   [RouterC] bgp 65009

   [RouterC-bgp] router-id 3.3.3.3

   [RouterC-bgp] peer 200.1.2.2 as-number 65008

   [RouterC-bgp] peer 9.1.1.1 as-number 65009

   [RouterC-bgp] ipv4-family unicast

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

   [RouterC-bgp-af-ipv4] quit

   [RouterC-bgp] quit

   # View the routing table of Router A.

   [RouterA] display bgp routing-table 9.1.1.0 24
   
    BGP local router ID : 1.1.1.1
    Local AS number : 65008
    Paths:   2 available, 1 best, 1 select
    BGP routing table entry information of 9.1.1.0/24:
    From: 200.1.1.1 (2.2.2.2)
    Route Duration: 00h00m56s
    Direct Out-interface: GigabitEthernet1/0/0
    Original nexthop: 200.1.1.1
    Qos information : 0x0
    AS-path 65009, origin igp, MED 0, pref-val 0, valid, external, best, select, pre 255
    Advertised to such 2 peers:
       200.1.1.1
       200.1.2.1
   
    BGP routing table entry information of 9.1.1.0/24:
    From: 200.1.2.1 (3.3.3.3)
    Route Duration: 00h00m06s
    Direct Out-interface: GigabitEthernet2/0/0
    Original nexthop: 200.1.2.1
    Qos information : 0x0
    AS-path 65009, origin igp, MED 0, pref-val 0, valid, external, pre 255, not preferred for router ID
    Not advertised to any peer yet

   The preceding command output shows that there are two valid routes to destination 9.1.1.0/24. The route with the next-hop address of 200.1.1.1 is the optimal route because the router ID of Router is smaller.

3. Set MED attributes for routes.

   # Apply a routing policy to set an MED value for the route advertised by Router B to Router A (the default MED value of a route is 0).

   [RouterB] route-policy policy10 permit node 10

   [RouterB-route-policy] apply cost 100

   [RouterB-route-policy] quit

   [RouterB] bgp 65009

   [RouterB-bgp] peer 200.1.1.2 route-policy policy10 export

   # View the routing table of Router A.

   [RouterA] display bgp routing-table 9.1.1.0 24
   
   BGP local router ID : 1.1.1.1
    Local AS number : 65008
    Paths:   2 available, 1 best, 1 select
    BGP routing table entry information of 9.1.1.0/24:
    From: 200.1.2.1 (3.3.3.3)
    Route Duration: 00h07m45s
    Direct Out-interface: GigabitEthernet2/0/0
    Original nexthop: 200.1.2.1
    Qos information : 0x0
    AS-path 65009, origin igp, MED 0, pref-val 0, valid, external, best, select, pre 255
    Advertised to such 2 peers:
       200.1.1.1
       200.1.2.1
   
    BGP routing table entry information of 9.1.1.0/24:
    From: 200.1.1.1 (2.2.2.2)
    Route Duration: 00h00m08s
    Direct Out-interface: GigabitEthernet1/0/0
    Original nexthop: 200.1.1.1
    Qos information : 0x0
    AS-path 65009, origin igp, MED 100, pref-val 0, valid, external, pre 255, not preferred for MED
    Not advertised to any peer yet

   The preceding command output shows that the MED value of the route with the next-hop address of 200.1.1.1 (Router B) is 100 and the MED value of the route with the next-hop address of 200.1.2.1 is 0. The route with the smaller MED value is selected.