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Example: Configuring the MED Using Route Filters

Requirements

No special configuration beyond device initialization is required before you configure this example.

Overview

To configure a route-filter policy that modifies the advertised MED metric in BGP update messages, include the metric statement in the policy action.

Figure 1 shows a typical network with internal peer sessions and multiple exit points to a neighboring autonomous system (AS).

Figure 1: Typical Network with IBGP Sessions and Multiple Exit Points

Device R4 has multiple loopback interfaces configured to simulate advertised prefixes. The extra loopback interface addresses are 44.44.44.44/32 and 144.144.144.144/32. This example shows how to configure Device R4 to advertise a MED value of 30 to Device R3 for all routes except 144.144.144.144. For 144.144.144.144, a MED value of 10 is advertised to Device 3. A MED value of 20 is advertised to Device R2, regardless of the route prefix.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Configuring Device R1

Step-by-Step Procedure

1. Configure the device interfaces.
   [edit interfaces fe-1/2/0 unit 1]user@R1# set family inet address 12.12.12.1/24
   [edit interfaces fe-1/2/1 unit 2]user@R1# set family inet address 13.13.13.1/24
   [edit interfaces lo0 unit 1]user@R1# set family inet address 192.168.1.1/32
2. Configure BGP.
   [edit protocols bgp group internal]user@R1# set type internaluser@R1# set local-address 192.168.1.1user@R1# set export send-directuser@R1# set neighbor 192.168.2.1user@R1# set neighbor 192.168.3.1
3. Configure OSPF.
   [edit protocols ospf area 0.0.0.0]user@R1# set interface lo0.1 passiveuser@R1# set interface fe-1/2/0.1user@R1# set interface fe-1/2/1.2
4. Configure a policy that accepts direct routes.

   Other useful options for this scenario might be to accept routes learned through OSPF or local routes.

   [edit policy-options policy-statement send-direct term 1]user@R1# set from protocol directuser@R1# set then accept
5. Configure the router ID and autonomous system (AS) number.
   [edit routing-options]user@R1# set autonomous-system 123user@R1# set router-id 192.168.1.1

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.

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

Configuring Device R2

Step-by-Step Procedure

1. Configure the device interfaces.
   [edit interfaces fe-1/2/0 unit 3]user@R2# set family inet address 12.12.12.21/24
   [edit interfaces fe-1/2/1 unit 4]user@R2# set family inet address 24.24.24.2/24
   [edit interfaces lo0 unit 2]user@R2# set family inet address 192.168.2.1/32
2. Configure BGP.
   [edit protocols bgp group internal]user@R2# set type internaluser@R2# set local-address 192.168.2.1user@R2# set export send-directuser@R2# set neighbor 192.168.1.1user@R2# set neighbor 192.168.3.1
   [edit protocols bgp group external]user@R2# set type externaluser@R2# set export send-directuser@R2# set peer-as 4user@R2# set neighbor 24.24.24.4
3. Configure OSPF.
   [edit protocols ospf area 0.0.0.0]user@R2# set interface lo0.2 passiveuser@R2# set interface fe-1/2/0.3user@R2# set interface fe-1/2/1.4
4. Configure a policy that accepts direct routes.

   Other useful options for this scenario might be to accept routes learned through OSPF or local routes.

   [edit policy-options policy-statement send-direct term 1]user@R2# set from protocol directuser@R2# set then accept
5. Configure the router ID and autonomous system (AS) number.
   [edit routing-options]user@R2# set autonomous-system 123user@R2# set router-id 192.168.2.1

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.

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

Configuring Device R3

Step-by-Step Procedure

1. Configure the device interfaces.
   [edit interfaces fe-1/2/0 unit 5]user@R3# set family inet address 13.13.13.3/24
   [edit interfaces fe-1/2/1 unit 6]user@R3# set family inet address 34.34.34.3/24
   [edit interfaces lo0 unit 3]user@R3# set family inet address 192.168.3.1/32
2. Configure BGP.
   [edit protocols bgp group internal]user@R3# set type internaluser@R3# set local-address 192.168.3.1user@R3# set export send-directuser@R3# set neighbor 192.168.1.1user@R3# set neighbor 192.168.2.1
   [edit protocols bgp group external]user@R3# set type externaluser@R3# set export send-directuser@R3# set peer-as 4user@R3# set neighbor 34.34.34.4
3. Configure OSPF.
   [edit protocols ospf area 0.0.0.0]user@R3# set interface lo0.3 passiveuser@R3# set interface fe-1/2/0.5user@R3# set interface fe-1/2/1.6
4. Configure a policy that accepts direct routes.

   Other useful options for this scenario might be to accept routes learned through OSPF or local routes.

   [edit policy-options policy-statement send-direct term 1]user@R3# set from protocol directuser@R3# set then accept
5. Configure the router ID and autonomous system (AS) number.
   [edit routing-options]user@R3# set autonomous-system 123user@R3# set router-id 192.168.3.1

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.

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

Configuring Device R4

Step-by-Step Procedure

1. Configure the device interfaces.
   [edit interfaces fe-1/2/0 unit 7]user@R4# set family inet address 24.24.24.4/24
   [edit interfaces fe-1/2/1 unit 8]user@R4# set family inet address 34.34.34.4/24
   [edit interfaces lo0 unit 4]user@R4# set family inet address 192.168.4.1/32user@R4# set family inet address 44.44.44.44/32user@R4# set family inet address 144.144.144.144/32

   Device R4 has multiple loopback interface addresses to simulate advertised prefixes.

2. Configure a policy that accepts direct routes.

   Other useful options for this scenario might be to accept routes learned through OSPF or local routes.

   [edit policy-options policy-statement send-direct term 1]user@R4# set from protocol directuser@R4# set then accept
3. Configure BGP.
   [edit protocols bgp group external]user@R4# set type externaluser@R4# set export send-directuser@R4# set peer-as 123
4. Configure the two MED policies.
   [edit policy-options]set policy-statement med-10 from route-filter 144.144.144.144/32 exact set policy-statement med-10 then metric 10 set policy-statement med-10 then accept
   set policy-statement med-30 from route-filter 0.0.0.0/0 longer set policy-statement med-30 then metric 30 set policy-statement med-30 then accept
5. Configure the two EBGP neighbors, applying the two MED policies to Device R3, and a MED value of 20 to Device R2.
   [edit protocols bgp group external]user@R4# set neighbor 34.34.34.3 export med-10user@R4# set neighbor 34.34.34.3 export med-30user@R4# set neighbor 24.24.24.2 metric-out 20
6. Configure the router ID and autonomous system (AS) number.
   [edit routing-options]user@R4# set autonomous-system 4user@R4# set router-id 192.168.4.1

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.

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

Verification

Confirm that the configuration is working properly.

• Checking the Active Path from Device R1 to Device R4
• Verifying That Device R4 Is Sending Its Routes Correctly

Checking the Active Path from Device R1 to Device R4

Purpose

Verify that the active path goes through Device R2.

Action

From operational mode, enter the show route protocol bgp command.

inet.0: 13 destinations, 19 routes (13 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

12.12.12.0/24       [BGP/170] 4d 01:13:32, localpref 100, from 192.168.2.1
                      AS path: I
                    > to 12.12.12.2 via fe-1/2/0.1
13.13.13.0/24       [BGP/170] 3d 05:36:10, localpref 100, from 192.168.3.1
                      AS path: I
                    > to 13.13.13.3 via fe-1/2/1.2
24.24.24.0/24       [BGP/170] 4d 01:13:32, localpref 100, from 192.168.2.1
                      AS path: I
                    > to 12.12.12.2 via fe-1/2/0.1
34.34.34.0/24       [BGP/170] 3d 05:36:10, localpref 100, from 192.168.3.1
                      AS path: I
                    > to 13.13.13.3 via fe-1/2/1.2
44.44.44.44/32     *[BGP/170] 00:06:03, MED 20, localpref 100, from 192.168.2.1
                      AS path: 4 I
                    > to 12.12.12.2 via fe-1/2/0.1
144.144.144.144/32 *[BGP/170] 00:06:03, MED 10, localpref 100, from 192.168.3.1
                      AS path: 4 I
                    > to 13.13.13.3 via fe-1/2/1.2
192.168.2.1/32      [BGP/170] 4d 01:13:32, localpref 100, from 192.168.2.1
                      AS path: I
                    > to 12.12.12.2 via fe-1/2/0.1
192.168.3.1/32      [BGP/170] 3d 05:36:10, localpref 100, from 192.168.3.1
                      AS path: I
                    > to 13.13.13.3 via fe-1/2/1.2
192.168.4.1/32     *[BGP/170] 00:06:03, MED 20, localpref 100, from 192.168.2.1
                      AS path: 4 I
                    > to 12.12.12.2 via fe-1/2/0.1

Meaning

The output shows that the preferred path to the routes advertised by Device R4 is through Device R2 for all routes except 144.144.144.144/32. For 144.144.144.144/32, the preferred path is through Device R3.

Verifying That Device R4 Is Sending Its Routes Correctly

Purpose

Make sure that Device R4 is sending update messages with a value of 20 to Device R2 and a value of 30 to Device R3.

Action

From operational mode, enter the show route advertising-protocol bgp command.

inet.0: 11 destinations, 13 routes (11 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 24.24.24.0/24           Self                 20                 I
* 34.34.34.0/24           Self                 20                 I
* 44.44.44.44/32          Self                 20                 I
* 144.144.144.144/32      Self                 20                 I
* 192.168.4.1/32          Self                 20                 I

inet.0: 11 destinations, 13 routes (11 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 24.24.24.0/24           Self                 30                 I
* 34.34.34.0/24           Self                 30                 I
* 44.44.44.44/32          Self                 30                 I
* 144.144.144.144/32      Self                 10                 I
* 192.168.4.1/32          Self                 30                 I

Meaning

The MED column shows that Device R4 is sending the correct MED values to its two EBGP neighbors.