CISCO交换机策略路由配置说明

Configuring Policy-Based RoutingYou can use policy-based routing (PBR) to configure a defined policy for traffic flows. By using PBR, you can have more control over routing by reducing the reliance on routes derived from routing protocols. PBR can specify and implement routing policies that allow or deny paths based on:•Identity of a particular end system•Application•ProtocolYou can use PBR to provide equal-access and source-sensitive routing, routing based on interactive versus batch traffic, or routing based on dedicated links. For example, you could transfer stock records to a corporate office on a high-bandwidth, high-cost link for a short time while transmitting routine application data such as e-mail over a low-bandwidth, low-cost link.With PBR, you classif y traffic using access control lists (ACLs) and then make traffic go through a different path. PBR is applied to incoming packets. All packets received on an interface with PBR enabled are passed through route maps. Based on the criteria defined in the route maps, packets are forwarded (routed) to the appropriate next hop.•If packets do not match any route map statements, all set clauses are applied.•If a statement is marked as permit and the packets do not match any route-map statements, the packets are sent through the normal forwarding channels, and destination-based routing is performed.•For PBR, route-map statements marked as deny are not supported.For more information about configuring route maps, see the "Using Route Maps to Redistribute Routing Information" section.You can use standard IP ACLs to specify match criteria for a source address or extended IP ACLs to specify match criteria based on an application, a protocol type, or an end station. The process proceeds through the route map until a match is found. If no match is found, normaldestination-based routing occurs. There is an implicit deny at the end of the list of match statements.If match clauses are satisfied, you can use a set clause to specify the IP addresses identifying the next hop router in the path.For details about PBR commands and keywords, see the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.2. For a list of PBR commands that are visible but not supported by the switch, see Appendix C, "Unsupported Commands inCisco IOS Release 12.2(35)SE,"Note This software release does not support PBR when processing IPv4 and IPv6 traffic.PBR Configuration GuidelinesBefore configuring PBR, you should be aware of this information:•To use PBR, you must have the IP services image installed on the switch.•Multicast traffic is not policy-routed. PBR applies to only to unicast traffic.•You can enable PBR on a routed port or an SVI.•The switch does not support route-map deny statements for PBR.•You can apply a policy route map to an EtherChannel port channel in Layer 3 mode, but you cannot apply a policy route map to a physical interface that is a member of the EtherChannel. If you try to do so, the command is rejected. When a policy route map is applied to a physical interface, that interface cannot become a member of an EtherChannel.•You can define a maximum of 246 IP policy route maps on the switch.•You can define a maximum of 512 access control entries (ACEs) for PBR on the switch.•When configuring match criteria in a route map, follow these guidelines:–Do not match ACLs that permit packets destined for a local address. PBR would forward these packets, which could cause ping or Telnet failure or route protocol flapping.–Do not match ACLs with deny ACEs. Packets that match a deny ACE are sent to the CPU, which could cause high CPU utilization.•To use PBR, you must first enable the routing template by using the sdm prefer routing global configuration command. PBR is not supported with the VLAN or default template. For more information on the SDM templates, see Chapter 7, "Configuring SDM Templates."•VRF and PBR are mutually exclusive on a switch interface. You cannot enable VRF when PBR is enabled on an interface. In contrast, you cannot enable PBR when VRF is enabled on an interface.•The number of TCAM entries used by PBR depends on the route map itself, the ACLs used, and the order of the ACLs and route-map entries.•Policy-based routing based on packet length, TOS, set interface, set default next hop, or set default interface are not supported. Policy maps with no valid set actions or with set action set to Don't Fragment are not supported.•Beginning with Cisco IOS Release 12.2(35)SE, the switch supports quality of service (QoS) DSCP and IP precedence matching in PBR route maps with these limitations:–You cannot apply QoS DSCP mutation maps and PBR route maps to the same interface.–You cannot configure DSCP transparency and PBR DSCP route maps on the same switch.–When you configure PBR with QoS DSCP, you can set QoS to be enabled (by entering the mls qos global configuration command) or disabled (by entering the no mls qos command). When QoS is enabled, to ensure that the DSCP value of the traffic is unchanged, you should configure DSCP trust state on the port where traffic enters the switch by entering the mls qos trust dscp interface configuration command. If the trust state is not DSCP, by default all nontrusted traffic would have the DSCP value marked to 0.Enabling PBRBy default, PBR is disabled on the switch. To enable PBR, you must create a route map that specifies the match criteria and the resulting action if all of the match clauses are met. Then, you must enable PBR for that route map on an interface. All packets arriving on the specified interface matching the match clauses are subject to PBR.PBR can be fast-switched or implemented at speeds that do not slow down the switch.Fast-switched PBR supports most match and set commands. PBR must be enabled before you enable fast-switched PBR. Fast-switched PBR is disabled by default.Packets that are generated by the switch, or local packets, are not normally policy-routed. When you globally enable local PBR on the switch, all packets that originate on the switch are subject to local PBR. Local PBR is disabled by default.Note To enable PBR, the switch must be running the IP services image.Beginning in privileged EX EC mode, follow these steps to configure PBR:•••Use the no route-map map-tag global configuration command or the no match or no setroute-map configuration commands to delete an entry. Use the no ip policy route-map map-tag interface configuration command to disable PBR on an interface. Use the no ip route-cache policyinterface configuration command to disable fast-switching PBR. Use the no ip local policy route-map map-tag global configuration command to disable policy-based routing on packets originating on the switch.。