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Example: Configuring a Routing Policy to Prepend the AS Path
This example shows how to configure a routing policy to prepend the AS path.
Requirements
Before you begin, make sure your router interfaces and protocols are correctly configured.
Overview
In this example, you create a routing policy called prependpolicy1 and a term called prependterm1. The routing policy prepends the AS numbers 1 1 1 1 to routes that are greater than or equal to 172.16.0.0/12, 192.168.0.0/16, and 10.0.0.0/8. The policy is applied as an import policy to all BGP routes and is evaluated when routes are imported to the routing table.
Topology
Configuration
Procedure
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.
set policy-options policy-statement prependpolicy1 term prependterm1 from route-filter 172.16.0.0/12 orlonger set policy-options policy-statement prependpolicy1 term prependterm1 from route-filter 192.168.0.0/16 orlonger set policy-options policy-statement prependpolicy1 term prependterm1 from route-filter 10.0.0.0/8 orlonger set policy-options policy-statement prependpolicy1 term prependterm1 then as-path-prepend "1 1 1 1" set policy-options policy-statement prependpolicy1 term prependterm1 from protocol direct set protocols bgp import prependpolicy1
Step-by-Step Procedure
The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.
To create a routing policy that prepends AS numbers to multiple routes:
Create the routing policy.
[edit] user@host# edit policy-options policy-statement prependpolicy1
Create the routing term.
[edit policy-options policy-statement prependpolicy1] user@host# edit term prependterm1
Specify the routes to prepend with AS numbers.
[edit policy-options policy-statement prependpolicy1 term prependterm1] user@host# set from route-filter 172.16.0.0/12 orlonger user@host# set from route-filter 192.168.0.0/16 orlonger user@host# set from route-filter 10.0.0.0/8 orlonger
Specify the AS numbers to prepend.
[edit policy-options policy-statement prependpolicy1 term prependterm1] user@host# set then as-path-prepend “1 1 1 1”
Note:If you enter multiple numbers, you must separate each number with a space. Enclose the numbers in double quotation marks.
Apply the policy as an import policy for all BGP routes.
[edit] user@host# set protocols bgp import prependpolicy1
Note:You can refer to the same routing policy one or more times in the same or different import statement.
Results
Confirm your configuration by entering the show policy-options and show protocols bgp commands from configuration mode. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.
user@host# show policy-options
policy-statement prependpolicy1 {
term prependterm1 {
from {
route-filter 172.16.0.0/12 orlonger;
route-filter 192.168.0.0/16 orlonger;
route-filter 10.0.0.0/8 orlonger;
}
then as-path-prepend "1 1 1 1";
}
}
user@host# show protocols bgp import prependpolicy1;
If you are done configuring the device, enter commit from configuration mode.
Verification
To confirm that the configuration is working properly, perform these tasks:
Verifying the AS Numbers to Prepend
Purpose
Verify that the policy and term are configured on the device and that the appropriate routes are specified to prepend with AS numbers.
Action
From operational mode, enter the show policy-options command.