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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 13

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Principle

Principle

This section describes implementation of routing policies.

A routing policy uses different matching rules and modes to select routes and change route attributes. Six filters in the routing policy can be used independently to filter routes in special scenarios. If the device supports the BGP to IGP function, the private attributes of BGP can serve as matching rules when the IGP imports BGP routes.

Routing Policy Principle

Figure 7-123 Working mechanism of the routing policy

As shown in Figure 7-123, a routing policy consists of N nodes (N ≥ 1). The system checks routes in the nodes of a routing policy with the node ID in ascending order. The If-match clauses define matching rules related to route attributes and six filters.

When a route matches all If-match clauses in a node, the route enters the matching mode without being checked in other nodes. The following two matching modes are supported:

  • permit: A route is permitted, and actions defined by the Apply clauses are performed on the route to set its attributes.
  • deny: A route is denied.

If a route does not match one If-match clause in a node, the route enters to the next node. If a route does not match any one of the nodes, the route is filtered out.

Filters

The six filters specified in If-match clauses in a routing policy are access control list (ACL), IP prefix list, AS_Path filter, community filter, extended community filter, and RD filter. The six filters have their own matching rules and modes. Therefore, they can be used independently to filter routes in some special situations.

ACL

ACLs check inbound interface, source or destination IP address, source or destination port number, and protocol of packets to filter routes. ACLs can be used independently when routing protocols advertise and receive routes. The If-match clauses in a routing policy support only basic ACLs.

ACLs can be used in not only a routing policy but other scenarios. For details, see "Principles" in the Configuration Guide - Security - ACL Configuration.

IP prefix list

IP prefix lists check IP prefixes of the source IP address, destination IP address, and next hop address to filter routes. They can be used independently when routing protocols advertise and receive routes.

Each IP prefix list consists of multiple indexes, and each index matches a node. An IP prefix list checks routes in all nodes with the indexes in ascending order. If a route matches one node, the route is no longer checked by other nodes. If a route does not match any one of the nodes, the route is filtered out.

The IP prefix list supports exact matching or matching within a specified mask length.

When the IP address is 0.0.0.0, a wildcard address, all routes in the mask length range are permitted or denied.

AS_Path filter

The AS_Path filter uses the AS_Path attribute of BGP to filter routes. It can be used independently when BGP advertises and receives routes.

The AS_Path attribute records all ASs that a route passes through. For details about the AS_Path attribute, see "Principles - BGP Concepts" in the Configuration Guide - IP Routing - BGP Configuration.

Community filter

The community filter uses the community attribute of BGP to filter routes. It can be used independently when BGP advertises and receives routes.

The community attribute identifies a group of routes with the same properties. For details about the community attribute, see "Principles - BGP Concepts" in the Configuration Guide - IP Routing - BGP Configuration.

Extcommunity Filter

The extended community filter uses the extended community attribute of BGP to filter routes. It can be used independently when VPN targets are used to identify routes in a VPN.

Currently, the extended community filter applies only to the VPN target attribute in a VPN. On a BGP/MPLS IP VPN, VPN targets are used to control the advertising and receiving of VPN routing information between sites. For details about the VPN target attribute, see "Principles - Concepts" in the Configuration Guide - VPN - BGP MPLS IP VPN Configuration.

Route Distinguisher (RD) filter

The RD filter uses the RD attribute in a VPN to filter routes. It can be used independently when the RD attribute is used to identify routes in a VPN.

A VPN instance uses RDs to separate address spaces and distinguish the IP prefixes with the same address space. For details about the RD attribute, see "Principles - Concepts" in the Configuration Guide - VPN - BGP MPLS IP VPN Configuration.

BGP to IGP function

The BGP to IGP function enables IGP to identify private attributes of BGP such as the community, extended community, and AS-Path attributes.

Routing policies can be used when an IGP imports BGP routes. BGP private attributes can be used as matching rules in routing policies only when the device supports the BGP to IGP function. When the device does not support the BGP to IGP function, the IGP cannot identify private attributes of BGP routes. Therefore, the matching rule does not take effect.

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Updated: 2019-12-13

Document ID: EDOC1000041694

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