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Table of Contents Expand all

play_arrow Understanding and Configuring Junos Routing Policies
- play_arrow Overview
- play_arrow Evaluating Routing Policies Using Match Conditions, Actions, Terms, and Expressions
- play_arrow Evaluating Complex Cases Using Policy Chains and Subroutines
- play_arrow Configuring Route Filters and Prefix Lists as Match Conditions
- play_arrow Configuring AS Paths as Match Conditions
- play_arrow Configuring Communities as Match Conditions
- play_arrow Increasing Network Stability with BGP Route Flapping Actions
- play_arrow Tracking Traffic Usage with Source Class Usage and Destination Class Usage Actions
- play_arrow Avoiding Traffic Routing Threats with Conditional Routing Policies
- play_arrow Protecting Against DoS Attacks by Forwarding Traffic to the Discard Interface
- play_arrow Improving Commit Times with Dynamic Routing Policies
  - Understanding Dynamic Routing Policies
  - Example: Configuring Dynamic Routing Policies
- play_arrow Testing Before Applying Routing Policies
  - Understanding Routing Policy Tests
  - Example: Testing a Routing Policy with Complex Regular Expressions
play_arrow Configuring Firewall Filters
play_arrow Configuring Traffic Policers
play_arrow Configuration Statements and Operational Commands
play_arrow Troubleshooting
- play_arrow Knowledge Base
  - https://kb.juniper.net/

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Conditional Advertisement and Import Policy (Routing Table) with certain match conditions

date_range 24-Nov-23

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BGP accepts all non-looped routes learned from neighbors and imports them into the RIB-In table. If these routes are accepted by the BGP import policy, they are then imported into the inet.0 routing table. In cases where only certain routes are required to be imported, provisions can be made such that the peer routing device exports routes based on a condition or a set of conditions.

The condition for exporting a route can be based on:

The peer the route was learned from
The interface the route was learned on
Some other required attribute

For example:

[edit]
policy-options {
    condition condition-name {
        if-route-exists address table table-name;
    }
}

This is known as conditional installation of prefixes and is described in Example: Configuring a Routing Policy for Conditional Advertisement Enabling Conditional Installation of Prefixes in a Routing Table.

Conditions in routing policies can be configured irrespective of whether they are a part of the export or import policies or both. The export policy supports these conditions inherited from the routing policy based on the existence of another route in the routing policy. However, the import policy doesn't support these conditions, and the conditions are not executed even if they are present.

Figure 1 illustrates where BGP import and export policies are applied. An import policy is applied to inbound routes that are visible in the output of the show route receive-protocol bgp neighbor-address command. An export policy is applied to outbound routes that are visible in the output of the show route advertising-protocol bgp neighbor-address command.

Figure 1: BGP Import and Export Policies

To enable conditional installation of prefixes, an export policy must be configured on the device where the prefix export has to take place. The export policy evaluates each route to verify that it satisfies all the match conditions under the from statement. It also searches for the existence of the route defined under the condition statement (also configured under the from statement).

If the route does not match the entire set of required conditions defined in the policy, or if the route defined under the condition statement does not exist in the routing table, the route is not exported to its BGP peers. Thus, a conditional export policy matches the routes for the desired route or prefix you want installed in the peers’ routing table.

To configure the conditional installation of prefixes with the help of an export policy:

Create a condition statement to check prefixes.

[edit]
policy-options {
    condition condition-name {
        if-route-exists address table table-name;
    }
}

Create an export policy with the newly created condition using the condition statement.

[edit]
policy-options {
    policy-statement policy-name {
        term 1 {
            from {
                protocols bgp;
                condition condition-name;
            }
            then {
                accept;
            }
        }
    }
}

Apply the export policy to the device that requires only selected prefixes to be exported from the routing table.
```
[edit]
protocols bgp {
    group group-name {
        export policy-name;
    }
}
```

arrow_backward PREVIOUS Example: Grouping Source and Destination Prefixes into a Forwarding Class

NEXT arrow_forward Conditional Advertisement Enabling Conditional Installation of Prefixes Use Cases

Routing Policies, Firewall Filters, and Traffic Policers User Guide

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Routing Policies, Firewall Filters, and Traffic Policers User Guide

Conditional Advertisement and Import Policy (Routing Table) with certain match conditions

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