Example: Enabling BGP Route Advertisements

Step-by-Step Procedure

The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.

To configure Device R1:

1. Configure the device interfaces.

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   [edit interfaces]
   user@R1# set xe-0/2/0 description R1-to-R2
   user@R1# set xe-0/2/0 unit 0 family inet address 10.0.0.1/30
   user@R1# set lo0 unit 0 family inet address 192.168.0.1/32
   

2. Configure BGP.

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   [edit protocols bgp group ext]
   user@R1# set type external
   user@R1# set peer-as 64511
   user@R1# set neighbor 10.0.0.2
   

3. Prevent routes from Device R3 from being hidden on Device R1 by including the loops 2 statement.

   The loops 2 statement means that the local device’s own AS number can appear in the AS path up to one time without causing the route to be hidden. The route is hidden if the local device’s AS number is detected in the path two or more times.

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   [edit protocols bgp family inet unicast]
   user@R1# set loops 2
   

4. Configure the routing policy that sends direct routes.

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   [edit policy-options policy-statement send-direct term 1]
   user@R1# set from protocol direct
   user@R1# set then accept
   

5. Apply the export policy to the BGP peering session with Device R2.

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   [edit protocols bgp group ext]
   user@R1# set export send-direct
   

6. Configure the autonomous system (AS) number.

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   [edit routing-options ]
   user@R1# set autonomous-system 64512
   

Step-by-Step Procedure

To configure Device R2:

1. Configure the device interfaces.

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   [edit interfaces]
   user@R2# set xe-0/2/0 description R2-to-R1
   user@R2# set xe-0/2/0 unit 0 family inet address 10.0.0.2/30
   user@R2# set xe-0/2/1 description R2-to-R3
   user@R2# set xe-0/2/1 unit 0 family inet address 10.1.0.1/30
   user@R2# set lo0 unit 0 family inet address 192.168.0.2/32
   

2. Configure BGP.

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   [edit  protocols bgp group ext]
   user@R2# set type external
   user@R2# set neighbor 10.0.0.1 peer-as 64512
   user@R2# set neighbor 10.1.0.2 peer-as 64512
   

3. Configure Device R2 to advertise routes learned from one EBGP peer to another EBGP peer in the same AS.

   In other words, advertise to Device R1 routes learned from Device R3 (and the reverse), even though Device R1 and Device R3 are in the same AS.

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   [edit  protocols bgp group ext]
   user@R2# set advertise-peer-as
   

4. Configure a routing policy that sends direct routes.

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   [edit policy-options policy-statement send-direct term 1]
   user@R2# set from protocol direct
   user@R2# set then accept
   

5. Apply the export policy.

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   [edit protocols bgp group ext]
   user@R2# set export send-direct
   

6. Configure the AS number.

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   [edit routing-options]
   user@R2# set autonomous-system 64511
   

Results

From configuration mode, confirm your configuration by entering the show interfaces, show protocols, show policy-options, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Device R1

user@R1# show interfaces
xe-0/2/0 {
    description R1-to-R2;
    unit 0 {
        family inet {
            address 10.0.0.1/30;
        }
    }
}
lo0 {
    unit 0 {
        family inet {
            address 192.168.0.1/32;
        }
    }
}

user@R1# show protocols
bgp {
    family inet {
        unicast {
            loops 2;
        }
    }
    group ext {
        type external;
        export send-direct;
        peer-as 64511;
        neighbor 10.0.0.2;
    }
}

user@R1# show policy-options
policy-statement send-direct {
    term 1 {
        from protocol direct;
        then accept;
    }
}

user@R1# show routing-options
autonomous-system 64512;

Device R2

user@R2# show interfaces
xe-0/2/0 {
    description R2-to-R1;
    unit 0 {
        family inet {
            address 10.0.0.2/30;
        }
    }
}
xe-0/2/1 {
    description R2-to-R3;
    unit 0 {
        family inet {
            address 10.1.0.1/30;
        }
    }
}
lo0 {
    unit 0 {
        family inet {
            address 192.168.0.2/32;
        }
    }
}

user@R2# show protocols
bgp {
    group ext {
        type external;
        advertise-peer-as;
        export send-direct;
        neighbor 10.0.0.1 {
            peer-as 64512;
        }
        neighbor 10.1.0.2 {
            peer-as 64512;
        }
    }
}

user@R2# show policy-options
policy-statement send-direct {
    term 1 {
        from protocol direct;
        then accept;
    }
}

user@R2# show routing-options
autonomous-system 64511;

If you are done configuring the devices, enter commit from configuration mode.

Purpose

Make sure that the routing tables on Device R1 and Device R3 contain the expected routes.

Action

1. On Device R2, deactivate the advertise-peer-as statement in the BGP configuration.

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   [edit  protocols bgp group ext]
   user@R2# deactivate advertise-peer-as
   user@R2# commit
   

2. On Device R3, deactivate the loops statement in the BGP configuration.

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   [edit  protocols bgp family inet unicast ]
   user@R3# deactivate unicast loops 
   user@R3# commit
   

3. On Device R1, check to see what routes are advertised to Device R2.

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   user@R1> show route advertising-protocol bgp 10.0.0.2
   inet.0: 5 destinations, 6 routes (5 active, 0 holddown, 0 hidden)
     Prefix                  Nexthop              MED     Lclpref    AS path
   * 10.0.0.0/30             Self                                    I
   * 192.168.0.1/32          Self                                    I
   

4. On Device R2, check to see what routes are received from Device R1.

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   user@R2> show route receive-protocol bgp 10.0.0.1
   inet.0: 7 destinations, 9 routes (7 active, 0 holddown, 0 hidden)
     Prefix                  Nexthop              MED     Lclpref    AS path
     10.0.0.0/30             10.0.0.1                                64512 I
   * 192.168.0.1/32          10.0.0.1                                64512 I

5. On Device R2, check to see what routes are advertised to Device R3.

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   user@R2> show route advertising-protocol bgp 10.1.0.2
   inet.0: 7 destinations, 9 routes (7 active, 0 holddown, 0 hidden)
     Prefix                  Nexthop              MED     Lclpref    AS path
   * 10.0.0.0/30             Self                                    I
   * 10.1.0.0/30             Self                                    I
   * 192.168.0.2/32          Self                                    I
   

6. On Device R2, activate the advertise-peer-as statement in the BGP configuration.

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   [edit  protocols bgp group ext]
   user@R2# activate advertise-peer-as
   user@R2# commit
   

7. On Device R2, recheck the routes that are advertised to Device R3.

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   user@R2> show route advertising-protocol bgp 10.1.0.2
   inet.0: 7 destinations, 9 routes (7 active, 0 holddown, 0 hidden)
     Prefix                  Nexthop              MED     Lclpref    AS path
   * 10.0.0.0/30             Self                                    I
   * 10.1.0.0/30             Self                                    I
   * 192.168.0.1/32          Self             64512 I
   * 192.168.0.2/32          Self                                    I
   * 192.168.0.3/32          10.1.0.2         64512 I

8. On Device R3, check the routes that are received from Device R2.

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   user@R3> show route receive-protocol bgp 10.1.0.1
   inet.0: 5 destinations, 6 routes (5 active, 0 holddown, 0 hidden)
     Prefix                  Nexthop              MED     Lclpref    AS path
   * 10.0.0.0/30             10.1.0.1                                64511 I
     10.1.0.0/30             10.1.0.1                                64511 I
   * 192.168.0.2/32          10.1.0.1                                64511 I

9. On Device R3, activate the loops statement in the BGP configuration.

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   [edit  protocols bgp family inet unicast ]
   user@R3# activate unicast loops 
   user@R3# commit
   

10. On Device R3, recheck the routes that are received from Device R2.

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    user@R3> show route receive-protocol bgp 10.1.0.1
    inet.0: 6 destinations, 8 routes (6 active, 0 holddown, 1 hidden)
      Prefix                  Nexthop              MED     Lclpref    AS path
    * 10.0.0.0/30             10.1.0.1                                64511 I
      10.1.0.0/30             10.1.0.1                                64511 I
    * 192.168.0.1/32          10.1.0.1                                64511 64512 I
    * 192.168.0.2/32          10.1.0.1                                64511 I
    

Meaning

First the advertise-peer-as statement and the loops statement are deactivated so that the default behavior can be examined. Device R1 sends to Device R2 a route to Device R1’s loopback interface address, 192.168.0.1/32. Device R2 does not advertise this route to Device R3. After activating the advertise-peer-as statement, Device R2 does advertise the 192.168.0.1/32 route to Device R3. Device R3 does not accept this route until after the loops statement is activated.