close

keyboard_arrow_left

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/

list Table of Contents

English

keyboard_arrow_right

Configuring Priority for Route Prefixes in RPD Infrastructure

date_range 24-Nov-23

arrow_backward

arrow_forward

Prefix prioritization helps users to prioritize certain routes or prefixes for better convergence and to provide differentiated services. In a network with a large number of routes, it is sometimes important to control the order in which routes get updated due to changes in the network topology. At a system level, Junos OS implements reasonable defaults based on heuristics to determine the order in which routes get updated. However, the default behavior is not always optimal. Prefix prioritization provides the user the ability to control the order in which the routes get updated from LDP or OSPF to rpd, and rpd to kernel. The Junos OS policy language is extended to let the user set relative priority (high and low) for prefixes through the existing import policy in protocols. Based on the tagged priority, the routes are placed in different priority queues. In the event of a topology change, high priority prefixes are updated in the routing table first, followed by low priority prefixes. Within the same priority level, routes will continue to be updated in lexicographic order. Routes that are not explicitly assigned a priority are treated as medium priority.

Before you begin to configure prefix prioritization in rpd for protocols such as OSPF, LDP, and BGP:

Configure the router interfaces.
Configure MPLS.
Configure the OSPF, BGP, and LDP protocols.

To configure the priority high for the OSPF protocol:

Configure the policy term.

content_copy zoom_out_map
[edit policy-options policy-statement policy-name]
user@host# set term term-name

For example:

content_copy zoom_out_map
[edit policy-options policy-statement ospf-prio]
user@host# set term t1

Configure the policy term to accept routes from OSPF.

content_copy zoom_out_map
[edit policy-options policy-statement ospf-prio  term t1]
user@host# set from protocol ospf

Specify the desired route as a match condition for which you want to set priority high.

content_copy zoom_out_map
[edit policy-options policy-statement ospf-prio term t1]
user@host# set from route-filter destination-prefix match-type

For example:

content_copy zoom_out_map
[edit policy-options policy-statement ospf-prio term t1]
user@host# set from route-filter 172.16.25.3/32 exact

Specify that the route is to be accepted and set priority high for the route if the previous conditions are matched.
```
[edit policy-options policy-statement ospf-prio term t1]
user@host# set then priority high
user@host# set then accept
```

Verify the configuration.

content_copy zoom_out_map
[edit]
user@host# show policy-options
policy-statement ospf-prio {
    term t1 {
        from {
            route-filter 172.16.25.3/32 exact;
            }
        then {
                priority high;
                accept;
                }
            }
    }

LDP inherits from OSPF.

To configure priority high for LDP:

Configure the policy term that imports from OSPF.

content_copy zoom_out_map
[edit policy-options policy-statement policy-name]
user@host# set term term-name

For example:

content_copy zoom_out_map
[edit policy-options policy-statement ospf-import]
user@host# set term ospf_ldp

Configure the term to accept routes and priority from OSPF.

content_copy zoom_out_map
[edit policy-options policy-statement ospf_import term ospf_ldp]
user@host# set from protocol ospf
user@host# set from route-filter destination-prefix match-type

For example:

content_copy zoom_out_map
[edit policy-options policy-statement ospf_import term ospf_ldp]
user@host# set from protocol ospf 
user@host# set from route-filter 172.16.25.3/32 exact

Verify the configuration.

content_copy zoom_out_map
[edit]
user@host# show policy-options
policy-statement ospf-import {
    term ospf_ldp {
        from {
            protocol ospf ;
            route-filter 172.16.25.3/32 exact;
            }
        then {
                priority high;
                accept;
                }
            }
    }

To configure the priority high for the BGP protocol:

Configure the policy term.

content_copy zoom_out_map
[edit policy-options policy-statement policy-name]
user@host# set term term-name

For example:

content_copy zoom_out_map
[edit policy-options policy-statement prio-for-bgp]
user@host# set term bgp_prio

Specify the desired route as a match condition.

content_copy zoom_out_map
[edit policy-options policy-statement prio-for-bgp term bgp_prio]
user@host# set from protocol bgp
user@host# set from route-filter destination-prefix match-type

For example:

content_copy zoom_out_map
[edit policy-options policy-statement prio-for-bgp term bgp_prio]
user@host# set from protocol bgp
user@host# set from route-filter 172.16.50.1/32 exact

Specify that the route is to be accepted and set the priority high for the route if the previous conditions are matched.
```
[edit policy-options policy-statement prio-for-bgp term bgp_prio]
user@host# set then priority high
user@host# set then accept
```

Verify the configuration.

content_copy zoom_out_map
policy-statement prio_for_bgp {
    term bgp_prio {
        from {
            protocol bgp;
            route-filter 172.16.50.1/32 exact;
            }
                then {
                    priority high;
                    accept;
                    }
    }
}

Note:

For BGP, you can also configure priority based on the route-distinguisher (RD) value in case of L3VPN. For example, you can configure priority for BGP with route-distinguisher 51.51.51.51:111.

To configure priority for BGP based on the route-distinguisher (RD) value:

Configure the policy term.

content_copy zoom_out_map
[edit policy-options policy-statement policy-name]
user@host# set term term-name

For example:

content_copy zoom_out_map
[edit policy-options policy-statement prio-for-bgp]
user@host# set term bgp_prio

Specify the desired route as a match condition.

content_copy zoom_out_map
[edit policy-options policy-statement prio-for-bgp term bgp_prio]
user@host# set from rib bgp.l3vpn.0
user@host# set from route-filter destination-prefix match-type
user@host# set from route-distinguisher route-distinguisher value

For example:

content_copy zoom_out_map
[edit policy-options policy-statement prio-for-bgp term bgp_prio]
user@host# set from rib bgp.l3vpn.0
user@host# set from route-filter 172.16.1.1/32 exact
user@host# set from route-distinguisher RD1

Specify that the route is to be accepted and set the priority high for the route if the previous conditions are matched.
```
[edit policy-options policy-statement prio-for-bgp term bgp_prio]
user@host# set then priority high
user@host# set then accept
```

Verify the configuration.

content_copy zoom_out_map
policy-statement prio_for_bgp {
    term bgp_prio {
        from {
            protocol rib bgp.l3vpn.0;
            route-filter 172.16.1.1/32 exact;
            route-distinguisher RD1;
            }
                then {
                    priority high;
                    accept;
                    }
    }
}

Note:

Low priority prefixes are installed only after the high priority prefixes in the routing table. You can also configure priority low similarly to priority high for the routes you want to set to low priority.

Note:

Priority is applied only when routes are pushed from RIB to FIB. Therefore, you cannot modify the priority of routes that are already installed. Changing the priority of routes already installed does not make sense. If you try changing the priority of routes already installed, there is a show output difference:

content_copy zoom_out_map
user@R1> show route 172.16.25.3 extensive | match state
 State: <FlashAll>   
              State:   <Active Int HighPriority>     <=== OSPF                 
        Validation State: unverified
        State: <FlashAll>   
              State:   <Active Int>                  <=== LDP                 
        Validation State: unverified          
    

As the route is already installed in FIB, LDP does not show the priority as High.

Restarting the routing daemon to remove the routes and adding it again reflects the proper priority from both the OSPF and LDP protocol perspective.

content_copy zoom_out_map
user@R1> restart routing
Routing protocols process signalled but still running, waiting 8 seconds more
Routing protocols process started, pid 4512

user@R1> show route 172.16.25.3 extensive |match state
 State: <FlashAll>   
              State:   <Active Int HighPriority>     <=== OSPF                 
        Validation State: unverified
        State: <FlashAll>   
              State:   <Active Int HighPriority>     <=== LDP                 
        Validation State: unverified          
    

arrow_backward PREVIOUS Example: Configuring the Priority for Route Prefixes in the RPD Infrastructure

NEXT arrow_forward Understanding AS Path Regular Expressions for Use as Routing Policy Match Conditions

Routing Policies, Firewall Filters, and Traffic Policers User Guide

Configuring Priority for Route Prefixes in RPD Infrastructure

Stay in touch

Helped me install or use the product
Accelerated my deployment

Discuss the product with a co-worker
Make a purchase inquiry

Routing Policies, Firewall Filters, and Traffic Policers User Guide

Configuring Priority for Route Prefixes in RPD Infrastructure

Related Documentation

Stay in touch