© 2006 Cisco Systems, Inc. All rights reserved.ONT v1.04-1 Implement the DiffServ QoS Model Configuring WFQ. - презентация

1 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Implement the DiffServ QoS Model Configuring WFQ

2 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Weighted Fair Queuing

3 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Weighted Fair Queuing A queuing algorithm should share the bandwidth fairly among flows by: –Reducing response time for interactive flows by scheduling them to the front of the queue –Preventing high-volume flows from monopolizing an interface In the WFQ implementation, conversations are sorted into flows and transmitted by the order of the last bit crossing its channel. Unfairness is reinstated by introducing weight to give proportionately more bandwidth to flows with higher IP precedence (lower weight).

4 © 2006 Cisco Systems, Inc. All rights reserved.ONT v WFQ Architecture and Benefits

5 © 2006 Cisco Systems, Inc. All rights reserved.ONT v WFQ Architecture WFQ uses per-flow FIFO queues.

6 © 2006 Cisco Systems, Inc. All rights reserved.ONT v WFQ Classification Packets of the same flow end up in the same queue.

7 © 2006 Cisco Systems, Inc. All rights reserved.ONT v WFQ Classification (Cont.) A fixed number of per-flow queues is configured. A hash function is used to translate flow parameters into a queue number. System packets (eight queues) and RSVP flows (if configured) are mapped into separate queues. Two or more flows could map into the same queue, resulting in lower per-flow bandwidth. Important: The number of queues configured has to be significantly larger than the expected number of flows.

8 © 2006 Cisco Systems, Inc. All rights reserved.ONT v WFQ Insertion and Drop Policy WFQ has two modes of dropping: –Early dropping when the congestive discard threshold is reached –Aggressive dropping when the hold-queue limit is reached WFQ always drops packets of the most aggressive flow. Drop mechanism exceptions: –A packet classified into an empty queue is never dropped. –The packet IP precedence has no effect on the dropping scheme.

9 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Benefits and Drawbacks of WFQ BenefitsSimple configuration (no need for classification to be configured) Guarantees throughput to all flows Drops packets of most aggressive flows Supported on most platforms Supported in most Cisco IOS versions DrawbacksPossibility of multiple flows ending up in one queue Lack of control over classification Supported only on links less than or equal to 2 Mb Cannot provide fixed bandwidth guarantees

10 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Configuring and Monitoring WFQ

11 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Configuring WFQ cdt: Number of messages allowed in each queue (a new threshold must be a power of 2 in the range from 16 to 4096; default is 64). When a conversation reaches this threshold, new message packets are discarded. dynamic-queues: Number of dynamic queues used for best-effort conversations (values are: 16, 32, 64, 128, 256, 512, 1024, 2048, and 4096; the default is 256). reservable-queues: Number of reservable queues used for reserved conversations in the range 0 to 1000 (used for interfaces configured for features such as RSVPthe default is 0). fair-queue [cdt [dynamic-queues [reservable- queues]]] router(config-if)#

12 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Additional WFQ Configuration Parameters hold-queue max-limit out router(config-if)# Specifies the maximum number of packets that can be in all output queues on the interface at any time. The default value for WFQ is Under special circumstances, WFQ can consume a lot of buffers, which may require lowering this limit.

13 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Monitoring WFQ show interface interface router> Displays interface delays including the activated queuing mechanism with the summary information Router>show interface serial 1/0 Hardware is M4T Internet address is /8 MTU 1500 bytes, BW 19 Kbit, DLY usec, rely 255/255, load 147/255 Encapsulation HDLC, crc 16, loopback not set Keepalive set (10 sec) Last input 00:00:00, output 00:00:00, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/4/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate bits/sec, 8 packets/sec 5 minute output rate bits/sec, 9 packets/sec... rest deleted...

14 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Monitoring WFQ (Cont.) show queue interface-name interface-number router> Displays detailed information about the WFQ system of the selected interface Router>show queue serial 1/0 Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 2/1000/64/0 (size/max total/threshold/drops) Conversations 2/4/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) (depth/weight/discards/tail drops/interleaves) 1/4096/0/0/0 Conversation 124, linktype: ip, length: 580 source: , destination: , id: 0x0166, ttl: 254, TOS: 0 prot: 6, source port 23, destination port (depth/weight/discards/tail drops/interleaves) 1/4096/0/0/0 Conversation 127, linktype: ip, length: 585 source: destination: , id: 0x020D, ttl: 252, TOS: 0 prot: 6, source port 23, destination port 11013

15 © 2006 Cisco Systems, Inc. All rights reserved.ONT v Summary WFQ was developed to overcome the limitations of the more basic queuing methods. Traffic is sorted into flows and transmitted by the order of the last bit crossing its channel. WFQ is automatically enabled on serial interfaces that have a default bandwidth of less than 2 Mbps. WFQ benefits include simple configuration and the dropping of packets of the most aggressive flows. However, a flow can end up in a queue of a different flow, WFQ does not allow manual classification, and if cannot provide fixed guarantees. WFQ is the basis for advanced queuing mechanisms like CBWFQ and LLQ.

16 © 2006 Cisco Systems, Inc. All rights reserved.ONT v