Enterprise QoS Solution Reference Network Design Guide

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Summary 1-32 Enterprise QoS Solution Reference Network Design Guide Chapter 1 Quality of Service Design Overview strategy was presented to illustrate how enterprises could start with simple QoS models and gradually increase their complexity as future needs arose. Executive endorsement is recommended, especially when choosing the select few applications to be serviced by the Mission-Critical data class. 2) Analyzing the service-level requirements of the various traffic classes to be provisioned for—the service level needs of voice, video, data and the control plane were discussed. Some of these highlights include the following: Voice requires 150 ms one-way, end-to-end (mouth-to-ear) delay, 30 ms of one-way jitter and no more than 1 % packet loss. Voice should receive strict priority servicing, and the amount of priority bandwidth assigned for it should take into account the VoIP codec, the packetization rate, IP/UDP/RTP headers (compressed or not) and Layer 2 overhead. Additionally, provisioning QoS for IP telephony requires that a minimal amount of guaranteed bandwidth be allocated to Call-Signaling traffic. Video comes in two flavors: Interactive Video and Streaming Video. Interactive Video has the same service level requirements as VoIP because a voice call is embedded within the video stream. Streaming Video has much laxer requirements, because of the high amount of buffering that has been built into the applications. Control plane requirements, such as provisioning moderate bandwidth guarantees for IP Routing and Network Management protocols, should not be overlooked. Data comes in a variety of forms, but can generally be classified into four main classes: Best Effort (the default class), Bulk (non-interactive, background flows), Transactional/Interactive (interactive, foreground flows) and Mission-Critical. Mission-Critical Data applications are locally-defined, meaning that each organization must determine the select few Transactional Data applications that contribute the most significantly to their overall business objectives. 3) Designing and testing QoS policies prior to production-network deployment—several best-practice QoS design principles were presented to help simplify and streamline the QoS design phase. These included: always performing QoS policies in hardware – rather than software – whenever a choice exists, classifying and marking (with standards-based DSCP markings) as close to the source as technically and administratively feasible, policing as close to the source as possible, and queuing on every node that has a potential for congestion. Queuing guidelines also included not provisioning more than 33% of a link for realtime traffic and reserving at least 25% of a link for the default Best Effort class. 4) Rolling-out the tested QoS designs to the production-network – Once the QoS designs have been finalized and PoC tested, it is vital ensure that the networking team thoroughly understands the QoS features and syntax before enabling features on production networks. Furthermore, it is recommended to schedule network downtime in order to rollout QoS features. A pilot network-segment can be selected for an initial deployment, and pending observation, the rollout can be expanded in stages to encompass the entire enterprise. A rollback strategy is always recommended, to address unexpected issues arising from the QoS deployment. 5) Monitoring service levels to ensure that the QoS objectives are being met – Implementing a QoS solution is not a one-time task that is complete upon policy deployment. A successful QoS policy rollout is followed by ongoing monitoring of service levels and periodic adjustments and tuning of QoS policies. As business conditions change, the enterprise may need to adapt to these changes and may be required to begin the QoS deployment cycle anew, by redefining their objectives, tuning and testing corresponding designs, rolling these new designs out and monitoring them to see if they match the redefined objectives. The document concluded by addressing the highly-relevant question: How can QoS tools be used to mitigate DoS/Worm Attacks? Version 3.3
Chapter 1 Quality of Service Design Overview References Standards Books Cisco Documentation Version 3.3 Enterprise QoS Solution Reference Network Design Guide References A “less-than-Best-Effort” traffic class, called Scavenger, was introduced, and a strategy for using this class for DoS/worm mitigation was presented. Specifically, flows can be monitored and policed at the Campus Access-Edge (and also at the Distribution Layer if Catalyst 6500s with Supervisor 720s are used). Out-of-profile flows can be marked down to the Scavenger marking (of DSCP CS1). To complement these policers, queues providing a “less-than-Best-Effort” Scavenger service during periods of congestion can be deployed in the LAN, WAN and VPN. Such a strategy would not penalize legitimate traffic flows that were temporarily out of profile; however sustained abnormal streams, highly-indicative of DoS/worm attacks, would be subject to aggressive dropping only after legitimate traffic was fully serviced. It is critically important to recognize, that even when Scavenger-class QoS has been deployed end-to-end, this strategy only mitigates DoS/worm attacks, and does not prevent them or remove them entirely. Therefore, it is vital to overlay security, firewall, intrusion detection, identity, Cisco Guard, Cisco Traffic Anomaly Detctor and Cisco Security Agent solutions in addition to QoS-enabled infrastructures. RFC 791 “Internet Protocol Protocol Specification” http://www.ietf.org/rfc/rfc791 RFC 2474 "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers http://www.ietf.org/rfc/rfc2474 RFC 2597 "Assured Forwarding PHB Group" http://www.ietf.org/rfc/rfc2597 RFC 2697 "A Single Rate Three Color Marker" http://www.ietf.org/rfc/rfc2697 RFC 2698 "A Two Rate Three Color Marker" http://www.ietf.org/rfc/rfc2698 RFC 3168 "The Addition of Explicit Congestion Notification (ECN) to IP" http://www.ietf.org/rfc/rfc3168 RFC 3246 "An Expedited Forwarding PHB (Per-Hop Behavior)" http://www.ietf.org/rfc/rfc3246 Szigeti, Tim and Christina Hattingh. End-to-End QoS Network Design: Quality of Service in LANs, WANs and VPNs. Indianapolis: Cisco Press, 2004. Cisco IOS QoS Configuration Guide – Cisco IOS version 12.3 http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/qos_vcg.htm Cisco IOS Configuration Guide – Configuring Data Link Switching Plus - Cisco IOS version 12.3 http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fibm_c/bcfpart2/bcfdls w.htm Understanding How Routing Updates and Layer 2 Control Packets Are Queued on an Interface with a QoS Service Policy (PAK_PRIORITY) http://www.cisco.com/warp/public/105/rtgupdates.html 1-33
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