- play_arrow Understanding and Configuring Junos Routing Policies
- play_arrow Overview
- Policy Framework Overview
- Comparison of Routing Policies and Firewall Filters
- Prefix Prioritization Overview
- FIB Prefix Prioritization
- Accounting of the Policer Overhead Attribute at the Interface Level
- Configuring the Accounting of Policer Overhead in Interface Statistics
- Understanding Routing Policies
- Protocol Support for Import and Export Policies
- Example: Applying Routing Policies at Different Levels of the BGP Hierarchy
- Default Routing Policies
- Example: Configuring a Conditional Default Route Policy
- play_arrow Evaluating Routing Policies Using Match Conditions, Actions, Terms, and Expressions
- How a Routing Policy Is Evaluated
- Categories of Routing Policy Match Conditions
- Routing Policy Match Conditions
- Route Filter Match Conditions
- Actions in Routing Policy Terms
- Summary of Routing Policy Actions
- Example: Configuring a Routing Policy to Advertise the Best External Route to Internal Peers
- Example: Configuring BGP to Advertise Inactive Routes
- Example: Using Routing Policy to Set a Preference Value for BGP Routes
- Example: Enabling BGP Route Advertisements
- Example: Rejecting Known Invalid Routes
- Example: Using Routing Policy in an ISP Network
- Understanding Policy Expressions
- Understanding Backup Selection Policy for OSPF Protocol
- Configuring Backup Selection Policy for the OSPF Protocol
- Configuring Backup Selection Policy for IS-IS Protocol
- Example: Configuring Backup Selection Policy for the OSPF or OSPF3 Protocol
- play_arrow Evaluating Complex Cases Using Policy Chains and Subroutines
- play_arrow Configuring Route Filters and Prefix Lists as Match Conditions
- Understanding Route Filters for Use in Routing Policy Match Conditions
- Understanding Route Filter and Source Address Filter Lists for Use in Routing Policy Match Conditions
- Understanding Load Balancing Using Source or Destination IP Only
- Configuring Load Balancing Using Source or Destination IP Only
- Walkup for Route Filters Overview
- Configuring Walkup for Route Filters to Improve Operational Efficiency
- Example: Configuring Route Filter Lists
- Example: Configuring Walkup for Route Filters Globally to Improve Operational Efficiency
- Example: Configuring Walkup for Route Filters Locally to Improve Operational Efficiency
- Example: Configuring a Route Filter Policy to Specify Priority for Prefixes Learned Through OSPF
- Example: Configuring the MED Using Route Filters
- Example: Configuring Layer 3 VPN Protocol Family Qualifiers for Route Filters
- Understanding Prefix Lists for Use in Routing Policy Match Conditions
- Example: Configuring Routing Policy Prefix Lists
- Example: Configuring the Priority for Route Prefixes in the RPD Infrastructure
- Configuring Priority for Route Prefixes in RPD Infrastructure
- play_arrow Configuring AS Paths as Match Conditions
- Understanding AS Path Regular Expressions for Use as Routing Policy Match Conditions
- Example: Using AS Path Regular Expressions
- Understanding Prepending AS Numbers to BGP AS Paths
- Example: Configuring a Routing Policy for AS Path Prepending
- Understanding Adding AS Numbers to BGP AS Paths
- Example: Advertising Multiple Paths in BGP
- Improve the Performance of AS Path Lookup in BGP Policy
- play_arrow Configuring Communities as Match Conditions
- Understanding BGP Communities, Extended Communities, and Large Communities as Routing Policy Match Conditions
- Understanding How to Define BGP Communities and Extended Communities
- How BGP Communities and Extended Communities Are Evaluated in Routing Policy Match Conditions
- Example: Configuring Communities in a Routing Policy
- Example: Configuring Extended Communities in a Routing Policy
- Example: Configuring BGP Large Communities
- Example: Configuring a Routing Policy Based on the Number of BGP Communities
- Example: Configuring a Routing Policy That Removes BGP Communities
- play_arrow Increasing Network Stability with BGP Route Flapping Actions
- play_arrow Tracking Traffic Usage with Source Class Usage and Destination Class Usage Actions
- Understanding Source Class Usage and Destination Class Usage Options
- Source Class Usage Overview
- Guidelines for Configuring SCU
- System Requirements for SCU
- Terms and Acronyms for SCU
- Roadmap for Configuring SCU
- Roadmap for Configuring SCU with Layer 3 VPNs
- Configuring Route Filters and Source Classes in a Routing Policy
- Applying the Policy to the Forwarding Table
- Enabling Accounting on Inbound and Outbound Interfaces
- Configuring Input SCU on the vt Interface of the Egress PE Router
- Mapping the SCU-Enabled vt Interface to the VRF Instance
- Configuring SCU on the Output Interface
- Associating an Accounting Profile with SCU Classes
- Verifying Your SCU Accounting Profile
- SCU Configuration
- SCU with Layer 3 VPNs Configuration
- Example: Grouping Source and Destination Prefixes into a Forwarding Class
- play_arrow Avoiding Traffic Routing Threats with Conditional Routing Policies
- Conditional Advertisement and Import Policy (Routing Table) with certain match conditions
- Conditional Advertisement Enabling Conditional Installation of Prefixes Use Cases
- Example: Configuring a Routing Policy for Conditional Advertisement Enabling Conditional Installation of Prefixes in a Routing Table
- play_arrow Protecting Against DoS Attacks by Forwarding Traffic to the Discard Interface
- play_arrow Improving Commit Times with Dynamic Routing Policies
- play_arrow Testing Before Applying Routing Policies
-
- play_arrow Configuring Traffic Policers
- play_arrow Understanding Traffic Policers
- Policer Implementation Overview
- ARP Policer Overview
- Example: Configuring ARP Policer
- Understanding the Benefits of Policers and Token Bucket Algorithms
- Determining Proper Burst Size for Traffic Policers
- Control Network Access Using Traffic Policing Overview
- Traffic Policer Types
- Order of Policer and Firewall Filter Operations
- Understanding the Frame Length for Policing Packets
- Supported Standards for Policing
- Hierarchical Policer Configuration Overview
- Understanding Enhanced Hierarchical Policers
- Packets-Per-Second (pps)-Based Policer Overview
- Guidelines for Applying Traffic Policers
- Policer Support for Aggregated Ethernet Interfaces Overview
- Example: Configuring a Physical Interface Policer for Aggregate Traffic at a Physical Interface
- Firewall and Policing Differences Between PTX Series Packet Transport Routers and T Series Matrix Routers
- Hierarchical Policers on ACX Series Routers Overview
- Guidelines for Configuring Hierarchical Policers on ACX Series Routers
- Hierarchical Policer Modes on ACX Series Routers
- Processing of Hierarchical Policers on ACX Series Routers
- Actions Performed for Hierarchical Policers on ACX Series Routers
- Configuring Aggregate Parent and Child Policers on ACX Series Routers
- play_arrow Configuring Policer Rate Limits and Actions
- play_arrow Configuring Layer 2 Policers
- Hierarchical Policers
- Configuring a Policer Overhead
- Two-Color and Three-Color Policers at Layer 2
- Layer 2 Traffic Policing at the Pseudowire Overview
- Configuring a Two-Color Layer 2 Policer for the Pseudowire
- Configuring a Three-Color Layer 2 Policer for the Pseudowire
- Applying the Policers to Dynamic Profile Interfaces
- Attaching Dynamic Profiles to Routing Instances
- Using Variables for Layer 2 Traffic Policing at the Pseudowire Overview
- Configuring a Policer for the Complex Configuration
- Creating a Dynamic Profile for the Complex Configuration
- Attaching Dynamic Profiles to Routing Instances for the Complex Configuration
- Verifying Layer 2 Traffic Policers on VPLS Connections
- Understanding Policers on OVSDB-Managed Interfaces
- Example: Applying a Policer to OVSDB-Managed Interfaces
- play_arrow Configuring Two-Color and Three-Color Traffic Policers at Layer 3
- Two-Color Policer Configuration Overview
- Basic Single-Rate Two-Color Policers
- Bandwidth Policers
- Prefix-Specific Counting and Policing Actions
- Policer Overhead to Account for Rate Shaping in the Traffic Manager
- Three-Color Policer Configuration Overview
- Applying Policers
- Three-Color Policer Configuration Guidelines
- Basic Single-Rate Three-Color Policers
- Basic Two-Rate Three-Color Policers
- Example: Configuring a Two-Rate Three-Color Policer
- play_arrow Configuring Logical and Physical Interface Traffic Policers at Layer 3
- play_arrow Configuring Policers on Switches
- Overview of Policers
- Traffic Policer Types
- Understanding the Use of Policers in Firewall Filters
- Understanding Tricolor Marking Architecture
- Configuring Policers to Control Traffic Rates (CLI Procedure)
- Configuring Tricolor Marking Policers
- Understanding Policers with Link Aggregation Groups
- Understanding Color-Blind Mode for Single-Rate Tricolor Marking
- Understanding Color-Aware Mode for Single-Rate Tricolor Marking
- Understanding Color-Blind Mode for Two-Rate Tricolor Marking
- Understanding Color-Aware Mode for Two-Rate Tricolor Marking
- Example: Using Two-Color Policers and Prefix Lists
- Example: Using Policers to Manage Oversubscription
- Assigning Forwarding Classes and Loss Priority
- Configuring Color-Blind Egress Policers for Medium-Low PLP
- Configuring Two-Color and Three-Color Policers to Control Traffic Rates
- Verifying That Two-Color Policers Are Operational
- Verifying That Three-Color Policers Are Operational
- Troubleshooting Policer Configuration
- Troubleshooting Policer Configuration
-
- play_arrow Configuration Statements and Operational Commands
- play_arrow Troubleshooting
- play_arrow Knowledge Base
-
Router Data Flow Overview
The Junos® operating system (Junos OS) provides a policy framework, which is a collection of Junos OS policies that enable you to control flows of routing information and packets within the router.
Flow of Routing Information
Routing information is the information about routes learned by the routing protocols from a router’s neighbors. This information is stored in routing tables. The routing protocols advertise active routes only from the routing tables. An active route is a route that is chosen from all routes in the routing table to reach a destination.
To control which routes the routing protocols place in the routing tables and which routes the routing protocols advertise from the routing tables, you can configure routing policies, which are sets of rules that the policy framework uses to preempt default routing policies.
The Routing Engine, which runs the router's control plane software, handles the flow of routing information between the routing protocols and the routing tables and between the routing tables and the forwarding table. The Routing Engine runs the Junos OS and routing policies and stores the active router configuration, the master routing table, and the master forwarding table,
Flow of Data Packets
Data packets are chunks of data that transit the router as they are being forwarded from a source to a destination. When a router receives a data packet on an interface, it determines where to forward the packet by looking in the forwarding table for the best route to a destination. The router then forwards the data packet toward its destination through the appropriate interface.
The Packet Forwarding Engine, which is the central processing element of the router’s forwarding plane, handles the flow of data packets in and out of the router’s physical interfaces. Although the Packet Forwarding Engine contains Layer 3 and Layer 4 header information, it does not contain the packet data itself (the packet's payload).
To control the flow of data packets transiting the device as the packets are being forwarded from a source to a destination, you can apply stateless firewall filters to the input or output of the router’s or switch’s physical interfaces.
To enforce a specified bandwidth and maximum burst size for traffic sent or received on an interface, you can configure policers. Policers are a specialized type of stateless firewall filter and a primary component of the Junos OS class-of-service (CoS).
Flow of Local Packets
Local packets are chunks of data that are destined for or sent by the router. Local packets usually contain routing protocol data, data for IP services such as Telnet or SSH, and data for administrative protocols such as the Internet Control Message Protocol (ICMP). When the Routing Engine receives a local packet, it forwards the packet to the appropriate process or to the kernel, which are both part of the Routing Engine, or to the Packet Forwarding Engine.
The Routing Engine handles the flow of local packets from the router’s physical interfaces and to the Routing Engine.
To control the flow of local packets between the physical interfaces and the Routing Engine, you can apply stateless firewall filters to the input or output of the loopback interface. The loopback interface (lo0) is the interface to the Routing Engine and carries no data packets.
Interdependent Flows of Routing Information and Packets
Figure 1 illustrates the flow of data through a router. Although routing information flows and packet flows are very different from one another, they are also interdependent.
Routing policies determine which routes the Routing Engine places in the forwarding table. The forwarding table, in turn, has an integral role in determining the appropriate physical interface through which to forward a packet.
Stateless and Stateful Firewall Filters
A stateless firewall filter, also known as an access control list (ACL), does not statefully inspect traffic. Instead, it evaluates packet contents statically and does not keep track of the state of network connections. In contrast, a stateful firewall filter uses connection state information derived from other applications and past communications in the data flow to make dynamic control decisions.
The basic purpose of a stateless firewall filter is to enhance security through the use of packet filtering. Packet filtering enables you to inspect the components of incoming or outgoing packets and then perform the actions you specify on packets that match the criteria you specify. The typical use of a stateless firewall filter is to protect the Routing Engine processes and resources from malicious or untrusted packets.
