QoS: Classification of Locally Sourced Packets

Transcription

1 QoS: Classification of Locally Sourced Packets QoS: Classification of Locally Sourced Packets is an algorithm to govern queue assignments of egressing packets that originate from the Cisco Series route processors. These locally-sourced packets are directed to specific queues based on the IP precedent value of the packet, pak_priority flag setting, and the outbound QoS policy of the egress interface. This algorithm greatly reduces the possibility of locally-sourced packets being starved of bandwidth by high priority traffic on all Cisco Series line cards. Feature History for QoS: Classification of Locally Sourced Packets Release 12.0(28)S Modification This feature was introduced for all Cisco Series linecards Contents Information on QoS: Classification of Locally Sourced Packets, page 1 Configuration Scenarios, page 3 Additional References, page 7 Information on QoS: Classification of Locally Sourced Packets There are no specific configuration tasks or command line interfaces related to this feature. To understand how locally-sourced packets are handled in response to typical QoS configuration scenarios, you must understand the following concepts: Background Information and Benefits, page 2 Classification Scheme for Locally-Sourced Packets, page 2 Corporate Headquarters: Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA USA Copyright 2004 Cisco Systems, Inc. All rights reserved.

2 Information on QoS: Classification of Locally Sourced Packets QoS: Classification of Locally Sourced Packets Background Information and Benefits Previously, the handling of locally-sourced traffic varied among the Cisco Series line cards. This feature establishes a common behavior for all line cards to prevent possible starvation of bandwidth to locally-sourced packets by heavy flows of high-priority data traffic such as Voice over IP or video. Marking Vital Output Traffic from the Route Processor Some internally generated packets, such as Layer 3 routing protocol updates are vital to the basic functioning of the router and should not be controlled by QoS features. Similarly, Layer 2 keepalives, or control packets in general, should not be subject to random dropping by the WRED mechanism. Most vital traffic generated by a router is tagged with a pak_priority flag. Packets marked with pak_priority are not dropped by QoS features. All other packets are subject to QoS features enabled on the output interface. Handling Vital Traffic Inbound to the Route Processor A policing policy configured on an ingress interface should not drop important packets (such as, routing protocol updates). It is sometimes appropriate to handle router-generated traffic in the same way as user-generated traffic, that is, to classify the packets with respect to the enabled service policy, then apply the appropriate actions based on the class to which the packet is matched. An example of such packets are performance probes intended to measure the behavior incurred by packets of a specified class. Classification Scheme for Locally-Sourced Packets With QoS: Classification of Locally Sourced Packets, Route Processor packets are classified as Important Packets and Unimportant Packets. Important Packets have the pak_priority flag set for non-ip packets, or the IP precedence value set at 6 or 7 for IP packets. For MPLS packets, Important Packets are those with an EXP tag value of 6 or 7. The following control packets have the pak_priority flag set (Important Packets): ISIS PIMV2 OSPF HELLO RIP ES-IS DECNET PPP (LCP, LQR) HDLC keepalive ATM ARP ATM OAM FR SVC (Q.933) FR keepalive FR elmi status query STP spanning tree 2

3 QoS: Classification of Locally Sourced Packets Configuration Scenarios All other packets are classified as Unimportant Packets. If a Modular Quality of Service Command Line Interface (MQC) policy or legacy policy is not configured on the egress interface or subinterface, Important Packets egress out of the low-latency queue (LLQ). Unimportant packets egress out of the default queue (See the Restrictions section on page 5 for exceptions). If an MQC policy or legacy policy is configured on the egress interface or subinterface, then Unimportant Packets egress according to the policy. For ISE-based line cards, an MQC policy configured on the main interface can govern the behavior of the subinterfaces. (Such as, VLAN/DLCI groups.) Route Processor-generated packets directed towards the subinterface will conform with the main interface policy. Non-IP and tag packets with the pak_priority flag set are directing by the following rules: 1. Take the queue allocated for Precedence 6 packets 2. Take the queue allocated for Precedence 7 packets if there is no Precedence 6 queue 3. Take the default queue if there is neither a Precedence 7 queue nor a Precedence 6 queue Packets with the pak_priority flag set follow this sequence only for packets matched on IP Precedence. MPLS packets matched with match mpls experimental number 6 or match mpls experimental number 7 take the default queue. Configuration Scenarios This section explains how locally-sourced packets are handled in the following QoS egress interface configuration scenarios: Example 1: No Egress Policy Configured, page 3 Example 2: Egress Policy Without Queues Allocated for Precedence 6 and 7 Packets, page 4 Example 3: Egress Policy With Queues Allocated for IP Precedence 6 Packets, page 4 Example 4: Egress Policy With Queues Allocated for IP Precedence 6 Packets and Priority Packets, page 4 Explanations in this section describe how PING packets with differing precedence values are handled by each configuration. Example 1: No Egress Policy Configured In the case where no egress policy is configured, all the following packets on all the Cisco Series line cards are directed to the LLQ: IP packets with a Precedence value of 6 or 7 MPLS packets with an EXP tag value of 6 or 7 Packets with the pak_priority flag set All of the remaining are Unimportant packets and are directed to the default queue. Line cards based on Engine 0 have only a default queue on the interface until a policy is configured on the Egress side. 3

4 Configuration Scenarios QoS: Classification of Locally Sourced Packets Example 2: Egress Policy Without Queues Allocated for Precedence 6 and 7 Packets This scenario is true for all line cards based on Engine 0, Engine 2, Engine 3, and Engine 4+. The following WRED configuration fragment detects packets with a precedence value of 1: Class class-default random-detect precedence 1 10 packets 20 packets 1 Because the LLQ is not indicated called with the priority keyword in the configuration, and there is no need for a queue allocated for packets with Precedence values of 6 or 7, the locally-sourced packets are directed as follows: PING packets with Precedence values of 6 or 7 to the LLQ PING packets with EXP tags of 6 or 7 to the LLQ pak_priority packets to the LLQ All other packets are directed to the default queue. Example 3: Egress Policy With Queues Allocated for IP Precedence 6 Packets The following WRED configuration fragment detects packets with precedence values of 1 and 6: Class prec6 bandwidth percent 10 random-detect precedence 6 10 packets 20 packets 1 Class class-default random-detect precedence 1 10 packets 20 packets 1 Because a queue is allocated for the Precedence 6 the locally-sourced packets are directed on the outbound side as follows: PING packets with Precedence values of 6 to the queue allocated for Precedence 6 packets PING packets with Precedence values of 7 to the LLQ PING packets with EXP tags of 6 or 7 to the LLQ pak_priority packets to the queue for Precedence 6 packets All other packets are directed to the default queue. Example 4: Egress Policy With Queues Allocated for IP Precedence 6 Packets and Priority Packets The following WRED configuration fragment detects packets with precedence values of 1 and 6 as well as establishing a priority scheduling queue for the precedence 3 packets of class prec3: Class prec6 bandwidth percent 10 bandwidth remaining percent 10 random-detect precedence 6 10 packets 20 packets 1 4

5 QoS: Classification of Locally Sourced Packets Configuration Scenarios Class prec3 priority Class class-default random-detect precedence 1 10 packets 20 packets 1 Locally-sourced packets are directed on the outbound side as follows: PING packets with Precedence values of 6 to the queue allocated for Precedence 6 packets PING packets with Precedence values of 7 to the default queue (because prec3 class packets now occupy the LLQ) PING packets with EXP tags of 6 or 7 to the default queue (because prec3 class packets now occupy the LLQ) All other packets are directed to the default queue. For line cards based on Engine 3 or Engine 4+, PING packets with MPLS EXP tag 3 are directed to the default queue. For the line cards that do not support the match mpls experimental class-map configuration command, MPLS packets match to values set by the match ip precedence class-map configuration command. In Example 4, PING packets with MPLS EXP tag 3 coming from line cards based on Engine 0 and Engine 2 are directed to the priority queue because it matches the Prec3 priority class. Restrictions Individual differences among line cards are noted in the following sections: Information for the 3-port Gigabit Ethernet Line Card, page 5 Information for the 4-Port OC-12/STM-4 ATM ISE and 8-port OC03/STM1 ATM Line Cards, page 6 Information for OC-12 SRP Single Ring Line Cards, page 6 Information for 8-port Fast Ethernet 100baseFX, 8-port Fast Ethernet 100baseTX, and1-port Gigabit Ethernet Line Cards, page 6 Information for the 3-port Gigabit Ethernet Line Card Product Number: 3GE-GBIC-SC= This is an Engine 2 line card. If an egress policy is defined, use the queue from the policy. However, if the queue is not the LLQ, use the default queue. This is because there is only one non-llq per port supported on the 3-port Gigabit Ethernet line card and the non-llq is the default queue. 5

6 Configuration Scenarios QoS: Classification of Locally Sourced Packets Information for the 4-Port OC-12/STM-4 ATM ISE and 8-port OC03/STM1 ATM Line Cards Product Numbers: 4OC12X/ATM-MM-SC=, 4OC12X/ATM-IR-SC=, 8OC03/ATM/TS-MM-B=, 4OC12X/ATM-IR-SC= These are Engine 3 line cards. If a policy map is not attached to a virtual circuit (VC), all Route Processor-generated traffic will egress from the default queue (only one queue is configured per VC for such cases). If a policy map includes a QoS configuration (such as a bandwidth command) and is attached to a VC, an LLQ is automatically opened on this VC whether or not we explicitly configured an LLQ using the priority command. For the second case all Route Processor-generated traffic will egress out either of the LLQ (for Important Packets) or from the default queue (Unimportant Packet). Classification of packets as Important Packet and Unimportant Packet is done exactly as explained in the Classification Scheme for Locally-Sourced Packets section on page 2. Important Packets are packets that have the pak_priority flag set, or IP packets with precedence values of 6 and 7. For MPLS packets, Important Packets are those with an EXP tag of 6 or 7. OAM cells are treated as Important Packets. Everything else is an Unimportant Packet. All Route Processor-generated packets whether or not they are transmitted over Virtual Circuits, with or without policy map configured and regardless of their priority, egress without any Qadmit policy. This means that all Route Processor-generated packets are not dropped because of RED or qlimit thresholds. Information for OC-12 SRP Single Ring Line Cards Product Numbers: OC12/SRP-MM/SC-B=, OC12/SRP-IR/SC-B=, OC12/SRP-LR/SC-B=, OC12/SRP-XR/SC= These are Engine 1 line cards. Important Packets flow out of the default queue, not the LLQ. Information for 8-port Fast Ethernet 100baseFX, 8-port Fast Ethernet 100baseTX, and1-port Gigabit Ethernet Line Cards Product Numbers: 8FE-FX-SC-B=, 8FE-TX-RJ45-B=, GE-SX/LH-SC=, GE-GBIC-SC-B= These are Engine 1 line cards. Important Packets flow out of the default queue, not the LLQ. 6

7 QoS: Classification of Locally Sourced Packets Additional References Additional References For additional information related to QoS: Classification of Locally Sourced Packets, refer to the following references: Related Documents Related Topic QoS and Locally Generated Packets Configuring QoS, particularly policing and shaping. Document Title Understanding How Routing Updates and Layer 2 Control Packets Are Queued on an Interface with a QoS Service Policy QC: Cisco IOS Release 12.0 Quality of Service Solutions Configuration Guide CCVP, the Cisco logo, and Welcome to the Human Network are trademarks of Cisco Systems, Inc.; Changing the Way We Work, Live, Play, and Learn is a service mark of Cisco Systems, Inc.; and Access Registrar, Aironet, Catalyst, CCDA, CCDP, CCIE, CCIP, CCNA, CCNP, CCSP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco IOS, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Cisco Unity, Enterprise/Solver, EtherChannel, EtherFast, EtherSwitch, Fast Step, Follow Me Browsing, FormShare, GigaDrive, HomeLink, Internet Quotient, IOS, iphone, IP/TV, iq Expertise, the iq logo, iq Net Readiness Scorecard, iquick Study, LightStream, Linksys, MeetingPlace, MGX, Networkers, Networking Academy, Network Registrar, PIX, ProConnect, ScriptShare, SMARTnet, StackWise, The Fastest Way to Increase Your Internet Quotient, and TransPath are registered trademarks of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries. All other trademarks mentioned in this document or Website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0711R) Copyright 2004 Cisco Systems, Inc. All rights reserved. 7

8 Additional References QoS: Classification of Locally Sourced Packets 8