Lectures Top-Down Network Design - Chapter 13: Optimizing Your Network Design

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1. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Top-DNtkDiDown Network Design Chapter Thirteen Optimizing Your Network Design Copyright 2010 Cisco Press & Priscilla Oppenheimer Reasons to Optimize • Meet key business and technical goals • Use bandwidth efficiently • Control delay and jitter • Reduce serialization delay • Support preferential service for essential applications • Meet Quality of Service (QoS) requirements Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 1
2. Top-Down Network Design, Ch. 13: Optimizing Your Network Design IP Multicast Helps Optimize Bandwidth Usage • With IP multicast, you can send a high- volltiditjtlume multimedia stream just once instead of once for each user • Requires support for – Multicast addressing – Multicast registration (IGMP) – Multicast routing protocols IP Multicast Addressing • Uses Class D multicast destination address – 224.0.0.0 to 239.255.255.255 • Converted to a MAC-layer multicast destination address – The low-order 23 bits of the Class D address become the low-order 23 bits of the MAC-layer address – The top 9 bits of the Class D address are not used – The top 25 bits of the MAC-layer address are 0x01:00:5E followed by a binary 0 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 2
3. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Internet Group Management Protocol (IGMP) • Allows a host to join a multicast group • Host transmits a membership-report message to inform routers on the segment that traffic for a group should be multicast to the host’s segment • IGMPv2 has support for a router more quickly learning that the last host on a segment has left a group Multicast Routing Protocols • Becoming obsolete – Multicast OSPF (MOSPF) – Distance Vector Multicast Routing Protocol (DVMRP) • Still used – Protocol Independent Multicast ()(PIM) • Dense-Mode PIM • Sparse-Mode PIM Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 3
4. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Reducing Serialization Delay • Link-layer fragmentation and interleaving – Breaks up and reassembles frames – Multilink PPP –Frame Relay FRF.12 • Compressed Real Time Protocol – RTP is used for voice and video – Compressed RTP compresses the RTP, UDP, and IP header from 40 bytes to 2 to 4 bytes A Few Technologies for Meeting QoS Requirements • IETF controlled load service • IETF guaranteed service • IP precedence • IP differentiated services Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 4
5. Top-Down Network Design, Ch. 13: Optimizing Your Network Design IP Type of Service Field • The type of service field in the IP header is divided into two subfields – The 3-bit precedence subfield supports eight levels of priority – The 4-bit type of service subfield supports four types of service • Althoug h IP prece dence is s till use d, the type of service subfield was hardly ever used IP Type of Service Field Type of Service Subfield Bit0 34567 D = Delay T = Throughput Precedence D T R C 0 R = Reliability C = Cost Bit 0 8152431 Version Header Type of Service Total Length Length Identification Flags Fragment Offset Time to Live Protocol Header Checksum Source IP Address Destination IP Address Options Padding Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 5
6. Top-Down Network Design, Ch. 13: Optimizing Your Network Design IP Differentiated Services (DS) Field • RFC 2474 redefines the type of service field as the Differentiated Services (DS) field – Bits 0 through 5 are the Differentiated Services Codepoint (DSCP) subfield • Has essentially the same goal as the precedence subfield • Influences queuing and packet dropping decisions fIPkttfor IP packets at a rout er out ttitfput interface – Bits 6 and 7 are the Explicit Congestion Notification (ECN) subfield IP Differentiated Services (DS) Field 0 6 Differentiated Services Codepoint Explicit Congestion Notification 0 8 15 24 31 Version Header Differentiated Services Total Length Length Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 6
7. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Classifying LAN Traffic • IEEE 802.1p • Classifies traffic at the data-link layer • Supports eight classes of service • A switch can have a separate queue for each class and service the highest-priority queues first Cisco Switching Techniques • Process switching • Fast switching • NetFlow switching • Cisco Express Forwarding (CEF) Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 7
8. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Cisco Queuing Services • First in, first out (FIFO) queuing • Priority queuing • Custom queuing • Weighted fair queuing (WFQ) • Class-based WFQ (CBWFQ) • Low latency queuing (LLQ) START Priority Queuing NO Packet in high queue? NO Packet in medium YES queue? NO Packet in normal YES queue? NO Packet in low YES queue? YES Dispatch Packet Continue Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 8
9. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Custom Queuing START (with Queue 1) NO Packet in Queue? YES Reached YES transmission NO Next Queue Dispatch Packet window size? Low-Latency Queuing • One queue always gets the green light – Use this for voice • Combine this with class-based weighted fair queuing – Define traffic classes based on protocols, access control lists, and input interfaces – Assign characteristics to classes such as bandwidth required and the maximum number of packets that can be queued for the class Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 9
10. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Random Early Detection (RED) • Congestion avoidance rather than congestion management • Monitors traffic loads and randomly discards packets if congestion increases • Source nodes detect dropped packets and slow down – Works best with TCP • Weighted Random Early Detection • Cisco’s implementation uses IP precedence or the DS field instead of just randomly dropping packets Traffic Shaping • Manage and control network traffic to avoid bottlenecks • Avoid overwhelming a downstream router or link • Reduce outbound traffic for a flow to a configured bit rate – Queue bursts of traffic for that flow Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 10
11. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Committed Access Rate (CAR) • Cisco feature for classifying and policing tffitraffic on an i ncomi ng i itfnterface • Supports policies regarding how traffic that exceeds a certain bandwidth allocation should be handled • Can drop a packet or change the IP precedence or DSCP bits Summary • Optimization provides the high bandwidth, low delay, and controlled jitter required by many critical business applications • To minimize bandwidth utilization by multimedia applications, use IP multicast • To reduce serialization delay, use link fragmentation and compressed RTP • To support QoS and optimize performance, use IP precedence, DSCP, 802.1p. advanced switching and queuing methods, RED, CAR, etc. Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 11
12. Top-Down Network Design, Ch. 13: Optimizing Your Network Design Review Questions • Why is it important to optimize your netk?twork? • What has become of the IP type of service field? • What are some methods for marking packets to identify the need for priority handling? • Compare and contrast Cisco queuing services. Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 12