3600 Flow-based Wred

Flow-Based WRED Feature Summary Flow-based Weighted Random Early Detection (WRED) is a feature of WRED that forces WRED to afford greater fairness to all flows on an interface in regard to how packets are dropped. WRED relies on a measurement called the average queue length to determine when to drop packets. When the packet count of the average queue length is in the upper range, WRED begins dropping packets. At this point, WRED applies a nonzero drop probability to all packets that arrive on an interface, indiscriminate of the kinds of flows to which the packets belong. Before you consider the advantages that use of flow-based WRED offers, it helps to think about how WRED (without flow-based WRED configured) affects different kinds of packet flows. Even before flow-based WRED classifies packet flows, flows can be thought of as belonging to one of these categories:

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Nonadaptive flows, which are flows that do not respond to congestion

•

Fragile flows, which, though congestion-aware, have fewer packets buffered at a gateway than do robust flows

Robust flows, which on average have a uniform data rate and slow down in response to congestion

Because of its packet-drop behavior—that is, that all flows, even those with relatively fewer packets in the output queue, are susceptible to packet drop during periods of congestion—WRED tends toward bias against fragile flows. Though fragile flows have fewer buffered packets, they are dropped at the same rate as packets of other flows. Flow-based WRED relies on these two main approaches to remedy the problem of unfair packet drop:

•

It classifies incoming traffic into flows based on parameters such as destination and source addresses and ports.

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It maintains state about active flows, which are flows that have packets in the output queues.

Flow-based WRED uses this classification and state information to ensure that each flow does not consume more than its permitted share of the output buffer resources. Flow-based WRED determines which flows monopolize resources and it more heavily penalizes these flows. Here is how flow-based WRED ensures fairness among flows: it maintains a count of the number of active flows that exist through an output interface. Given the number of active flows and the output queue size, flow-based WRED determines the number of buffers available per flow.

Flow-Based WRED 1

Platforms

To allow for some burstiness, flow-based WRED scales the number of buffers available per flow by a configured factor and allows each active flow to have a certain number of packets in the output queue. This scaling factor is common to all flows. The outcome of the scaled number of buffers becomes the per-flow limit. When a flow exceeds the per-flow limit, the probability that a packet from that flow will be dropped increases.

Benefits •

Ensures that flows that respond to WRED packet drops by backing off packet transmission are protected from flows that do not respond to WRED packet drops.

•

Prohibits a single flow from monopolizing the buffer resources at an interface.

Restrictions WRED, custom queueing (CQ), priority queueing (PQ), and weighted fair queueing (WFQ) are mutually exclusive on an interface. The router software produces an error message if you configure WRED and any one of these queueing strategies simultaneously.

Platforms The flow-based WRED feature is supported on these Cisco router platforms:

• • • • • •

Cisco 1600 series. Cisco 2500 series Cisco 3600 series Cisco 4000 series (including 4500 and 4700 series) Cisco 7200 series On the RSP interface card on a Cisco 7500 series router.

Prerequisites Perform the following tasks before you configure flow-based WRED:

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Enable WRED, using the random-detect command.

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Optionally, configure parameters for packets with a specific IP Precedence using the random-detect precedence command.

Optionally, configure the weight factor used in calculating the average queue length using the random-detect exponential-weighting-constant command.

For complete information on these tasks and commands, see the Cisco IOS Release 12.0 Quality of Service Solutions Configuration Guide and the Cisco IOS Release 12.0 Quality of Service Solutions Command Reference.

Supported MIBs and RFCs None. 2

Cisco IOS Release 12.0(3)T

Restrictions

Configuration Task Before you can configure flow-based WRED, you must enable WRED and configure it. For complete information on the tasks and commands you use, see the Cisco IOS Release 12.0 Quality of Service Solutions Configuration Guide and the Cisco IOS Release 12.0 Quality of Service Solutions Command Reference. To configure an interface for flow-based WRED, use the following commands in the order specified in interface configuration mode: Step

Command

Purpose

1

random-detect flow

Enable flow-based WRED.

2

random-detect flow average-depth-factor scaling-factor

Set the flow threshold multiplier for flow-based WRED.

3

random-detect flow count number

Set the maximum flow count for flow-based WRED.

Configuration Examples The following example enables Weighted Random Early Detection (WRED) on the Serial1 interface and configures flow-based WRED. The random-detect command is used to enable WRED. Once WRED is enabled, the random-detect flow command can be used to enable flow-based WRED.

Flow-Based WRED 3

Configuration Examples

After flow-based WRED is turned on, the random-detect flow average-depth-factor is used to set the scaling factor to 8 and the random-detect flow count command is used to set the flow count to 16. The scaling factor is used to scale the number of buffers available per flow and to determine the number of packets allowed in the output queue for each active flow. Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#interface Serial1 Router(config-if)#random-detect Router(config-if)#random-detect flow Router(config-if)#random-detect flow average-depth-factor 8 Router(config-if)#random-detect flow count 16 Router(config-if)#end

This part of the example shows how the router is configured after the flow-based WRED commands are issued: Router#write terminal Building configuration... Current configuration: ! version 12.0 service timestamps debug datetime msec localtime service timestamps log uptime no service password-encryption service tcp-small-servers ! no logging console enable password lab ! clock timezone PST -8 clock summer-time PDT recurring ip subnet-zero no ip domain-lookup ! interface Ethernet0 no ip address no ip directed-broadcast no ip mroute-cache shutdown ! interface Serial0 no ip address no ip directed-broadcast no ip mroute-cache no keepalive shutdown ! interface Serial1 ip address 190.1.2.1 255.255.255.0 no ip directed-broadcast load-interval 30 no keepalive random-detect random-detect flow random-detect flow count 16 random-detect flow average-depth-factor 8 ! router igrp 8 network 190.1.0.0 ! ip classless no ip http server

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Restrictions

! line con 0 transport input none line 1 16 transport input all line aux 0 transport input all line vty 0 4 password lab login ! end

Flow-Based WRED 5

Command Reference

Command Reference This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command references.

• • • • • •

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random-detect flow random-detect flow average-depth-factor random-detect flow count show interfaces show queue show queueing

Cisco IOS Release 12.0(3)T

random-detect flow

random-detect flow To enable flow-based Weighted Random Early Detection (WRED), use the random-detect flow interface configuration command. The no form of this command disables flow-based WRED. random-detect flow no random-detect flow

Syntax Description This command has no arguments or keywords.

Default Flow-based WRED is disabled by default.

Command Mode Interface configuration

Usage Guidelines This command first appeared in Release 12.0(3)T. You must use this command to enable flow-based WRED before you can use the random-detect flow average-depth-factor and random-detect flow count commands to further configure the parameters of flow-based WRED. Before you can enable flow-based WRED, you must enable and configure WRED. For complete information, see the Cisco IOS Release 12.0 Quality of Service Solutions Configuration Guide and the Cisco IOS Release 12.0 Quality of Service Solutions Command Reference.

Example The following example enables flow-based WRED on the Serial1 interface: router(config)# interface Serial1 router(config-if)# random-detect flow

Related Commands random-detect exponential-weighting-constant random-detect flow average-depth-factor random-detect flow count random-detect precedence show interfaces show queue show queueing

Flow-Based WRED 7

Command Reference

random-detect flow average-depth-factor To set the multiplier to be used in determining the average depth factor for a flow when flow-based Weighted Random Early Detection (WRED) is enabled, use the random-detect flow average-depth-factor interface configuration command. The no form of this command removes the current flow average depth factor value. random-detect flow average-depth-factor scaling-factor no random-detect flow average-depth-factor scaling-factor

Syntax Description Syntax Description scaling-factor

The number 2, 4, 8 or 16. The default value is 4.

Default 4

Command Mode Interface configuration

Usage Guidelines This command first appeared in Release 12.0(3)T. Use this command to specify the scaling factor that flow-based WRED should use in scaling the number of buffers available per flow and in determining the number of packets allowed in the output queue for each active flow. This scaling factor is common to all flows. The outcome of the scaled number of buffers becomes the per-flow limit. If this command is not used and flow-based WRED is enabled, the average depth scaling factor defaults to 4. A flow is considered nonadaptive—that is, it takes up too much of the resources—when the average flow depth times the specified multiplier (scaling factor) is less than the flow’s depth, that is: average-flow-depth * (scaling factor) < flow-depth

Before you use this command, you must use the random-detect flow command to enable flow-based WRED for the interface. To configure flow-based WRED, you also use the random-detect flow count command.

Example The following example enables flow-based WRED on the Serial1 interface, sets the scaling factor for the average flow depth to 8: router(config)# interface Serial1 router(config-if)# random-detect flow router(config-if)# random-detect flow average-depth-factor 8

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random-detect flow average-depth-factor

Related Commands random-detect exponential-weighting-constant random-detect flow random-detect flow count random-detect precedence show interfaces show queue show queueing

Flow-Based WRED 9

Command Reference

random-detect flow count To set the flow count for flow-based Weighted Random Early Detection (WRED), use the random-detect flow count interface configuration command. The no form of this command removes the current flow count value. random-detect flow count number no random-detect flow count number

Syntax Description number

Specify a value from 0 to 215.

Default 256

Command Mode Interface configuration

Usage Guidelines This command first appeared in Release 12.0(3)T. Before you use this command, you must use the random-detect flow command to enable flow-based WRED for the interface.

Example The following example enables flow-based WRED on the Serial1 interface and sets the flow threshold constant to 16: router(config)# interface Serial1 router(config-if)# random-detect flow router(config-if)# random-detect flow count 16

Related Commands random-detect exponential-weighting-constant random-detect flow random-detect precedence show interfaces show queue show queueing

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show interfaces

show interfaces To display statistics for a specific interface or all interfaces on the router, use the show interfaces EXEC command. The resulting output varies depending on the network for which an interface has been configured. show interfaces [type slot / port-adapter / port] (for ports on VIP interface processors in the Cisco 7500 series routers)

Syntax Description type

(Optional) Type of interface.

slot

(Optional) Refer to the appropriate hardware manual for slot information.

port-adapter

(Optional) Refer to the appropriate hardware manual for information about port adapter compatibility.

port

(Optional) Refer to the appropriate hardware manual for port information.

Command Mode EXEC

Usage Guidelines This command first appeared in Cisco IOS Release 10.0. The show interfaces command displays statistics for the network interfaces. The output of the show interfaces command varies based on the interface type and configuration. This document describes the output related to these feature and services:

• • •

Flow-based WRED Distributed weighted fair queueing (DWFQ) Weighted Random Early Detection (DWRED)

Refer to the Cisco IOS Release 11.1 command reference documents for a complete description of the entire output.

Flow-Based WRED 11

Command Reference

Sample Display (Flow-based WRED) The following is sample output from the show interfaces command issued for the Serial1 interface for which flow WRED is enabled. The output shows that there are 8 active flow-based WRED flows, that the maximum number of flows active at any time is 9, and the maximum number of possible flows configured for the interface is 16.: Router#show interface Serial1 Serial1 is up, line protocol is up Hardware is HD64570 Internet address is 190.1.2.1/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliablility 255/255, txload 237/255, rxload 1/255 Encapsulation HDLC, loopback not set Keepalive not set Last input 00:00:22, output 00:00:00, output hang never Last clearing of "show interface" counters 00:17:58 Input queue: 0/75/0 (size/max/drops); Total output drops: 2479 Queueing strategy: random early detection(RED) flows (active/max active/max): 8/9/16 mean queue depth: 27 drops: class random tail min-th max-th mark-prob 0 946 0 20 40 1/10 1 488 0 22 40 1/10 2 429 0 24 40 1/10 3 341 0 26 40 1/10 4 235 0 28 40 1/10 5 40 0 31 40 1/10 6 0 0 33 40 1/10 7 0 0 35 40 1/10 rsvp 0 0 37 40 1/10 30 second input rate 1000 bits/sec, 2 packets/sec 30 second output rate 119000 bits/sec, 126 packets/sec 1346 packets input, 83808 bytes, 0 no buffer Received 12 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 84543 packets output, 9977642 bytes, 0 underruns 0 output errors, 0 collisions, 6 interface resets 0 output buffer failures, 0 output buffers swapped out 0 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up

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show interfaces

Sample Display (DWFQ) The following is sample output from the show interfaces command when DWFQ is enabled on an interface. Notice that the queueing strategy is listed as “VIP-based fair queuing.” Router# show interfaces FastEthernet1/1/0 FastEthernet1/1/0 is up, line protocol is up Hardware is cyBus FastEthernet Interface, address is 0007.f618.4448 (bia 00e0) Description: pkt input i/f for WRL tests (to pagent) Internet address is 80.0.2.70/24 MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive not set, fdx, 100BaseTX/FX ARP type: ARPA, ARP Timeout 04:00:00 Last input never, output 01:11:01, output hang never Last clearing of "show interface" counters 01:12:31 Queueing strategy: VIP-based fair queuing Output queue 0/40, 0 drops; input queue 0/75, 0 drops 30 second input rate 0 bits/sec, 0 packets/sec 30 second output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 watchdog, 0 multicast 0 input packets with dribble condition detected 1 packets output, 60 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffers copied, 0 interrupts, 0 failures

Sample Display (DWRED) The following is sample output from the show interfaces command when DWRED is enabled on an interface. Notice that the packet drop strategy is listed as “VIP-based weighted RED.” Router# show interfaces hssi0/0/0 Hssi0/0/0 is up, line protocol is up Hardware is cyBus HSSI Description: 45Mbps to R1 Internet address is 200.200.14.250/30 MTU 4470 bytes, BW 45045 Kbit, DLY 200 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:02, output 00:00:03, output hang never Last clearing of "show interface" counters never Queueing strategy: fifo Packet Drop strategy: VIP-based weighted RED Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 1976 packets input, 131263 bytes, 0 no buffer Received 1577 broadcasts, 0 runts, 0 giants 0 parity 4 input errors, 4 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 1939 packets output, 130910 bytes, 0 underruns 0 output errors, 0 applique, 3 interface resets 0 output buffers copied, 0 interrupts, 0 failures

Flow-Based WRED 13

Command Reference

Related Commands custom-queue-list fair-queue priority-group priority-list interface priority-list queue-limit queue-list interface queue-list queue byte-count random-detect random-detect flow average-depth-factor random-detect flow count show queueing

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show queue

show queue To list fair queueing configuration and statistics for a particular interface as flow-based WRED information, use the show queue privileged EXEC command. show queue interface-type interface-number

Syntax Description interface-type

The name of the interface.

interface-number

The number of the interface.

Command Mode Privileged EXEC

Usage Guidelines This command first appeared in Cisco IOS Release12.0. This command displays statistics for interfaces configured with the fair queueing strategy.

Sample Display The following is sample output from the show queue command issued for the Serial1 interface for which flow-based WRED is enabled and configured. The output shows information for each packet in the queue; the data identifies the packet by number, the flow-based queue to which the packet belongs, the protocol used, and so forth: Router#show queue Serial1 Output queue for Serial1 is 13/0 Packet 1, flow id: 264, linktype: ip, length: 118, flags: 0x88 source: 190.1.1.3, destination: 190.1.2.2, id: 0x0000, ttl: 59, prot: 0 data: 0x0001 0x0203 0x0405 0x0607 0x0809 0x0A0B 0x0C0D 0x0E0F 0x1011 0x1213 0x1415 0x1617 0x1819 0x1A1B Packet 2, flow id: 264, linktype: ip, length: 118, flags: 0x88 source: 190.1.1.4, destination: 190.1.2.2, id: 0x0000, ttl: 59, prot: 0 data: 0x0001 0x0203 0x0405 0x0607 0x0809 0x0A0B 0x0C0D 0x0E0F 0x1011 0x1213 0x1415 0x1617 0x1819 0x1A1B

Table 1describes the fields shown in this display. Table 1

Show Queue Field Descriptions for Flow-Based WRED

Field

Description

Packet

Packet number.

flow id

Flow-based WRED number.

linktype

Protocol name.

length

Packet length.

flags

Internal version-specific flags.

source

Source IP address. Flow-Based WRED 15

Command Reference

Field

Description

destination

Destination IP address

id

Packet ID.

ttl

Time to live count.

prot

Layer 4 protocol number.

data

Packet data.

The following is sample output from the show queue command when weighted fair queueing (WFQ) is configured. There are two active conversations on the serial 1 interface. WFQ ensures that both of these IP data streams, one TCP and other UDP, receive equal bandwidth on the interface while they have messages in the pipeline. Router# show queue serial1 Input queue: 0/75/0 (size/max/drops); Total output drops: 303628 Queueing strategy: weighted fair Output queue: 64/1000/64/303628 (size/max total/threshold/drops) Conversations 2/2/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) (depth/weight/discards/tail drops/interleaves) 45/4096/1123/0/0 Conversation 244, linktype: ip, length: 50 source: 55.1.1.1, destination: 66.1.1.2, id: 0x0000, ttl: 59, TOS: 0 prot: 6, source port 55, destination port 55 (depth/weight/discards/tail drops/interleaves) 19/4096/302541/0/0 Conversation 185, linktype: ip, length: 118 source: 55.1.1.1, destination: 66.1.1.2, id: 0x0000, ttl: 59, TOS: 0 prot: 17, source port 20, destination port 20

Table 2 describes the fields shown in this display.

.

Table 2

16

Show Queue Field Descriptions for WFQ

Field

Description

Input Queue

Input queue size in packets.

Total output drops

Total output packet drops.

Queueing strategy

Type of queueing active on this interface.

Output queue

Output queue size in packets.

Conversations

WFQ conversation number.

Reserved Conversations

Total number of reserved WFQ conversations. Default is 256.

depth

Queue depth for the conversation in packets.

weight

Weight used in WFQ.

discards

Number of packet discards for the conversation.

tail drops

Number of tail drop packets for the conversation.

interleaves

Number of packets interleaved.

linktype

Protocol name.

length

Packet length.

source

Source IP address.

Cisco IOS Release 12.0(3)T

show queue

Table 2

Show Queue Field Descriptions (Continued)for WFQ

Field

Description

destination

Destination IP address.

id

Packet ID.

ttl

Time to live count.

TOS

IP type of service.

prot

Layer 4 protocol number.

Related Commands custom-queue-list fair-queue priority-group priority-list interface priority-list queue-limit queue-list interface queue-list queue byte-count random-detect random-detect flow average-depth-factor random-detect flow count show interfaces show queueing

Flow-Based WRED 17

Command Reference

show queueing To list all or selected configured queueing strategies, use the show queueing privileged EXEC command. show queueing [custom | fair | priority | red]

Syntax Description custom

(Optional) Status of the custom queueing list configuration.

fair

(Optional) Status of the fair queueing configuration.

priority

(Optional) Status of the priority queueing list configuration.

red

(Optional) Status of the Weighted Random Early Detection (WRED) configuration, including configuration of flow-based WRED.

Default If no keyword is entered, this command shows the configuration of all interfaces.

Command Mode Privileged EXEC

Usage Guidelines This command first appeared in Cisco IOS Release 10.3.

Sample Displays The following is sample output from the show queueing custom command: Router# show queueing custom Current custom queue configuration: List 3 3 3 3

Queue 10 3 3 3

Args default interface Tunnel3 protocol ip byte-count 444 limit 3

The following is sample output from the show queueing command. There are two active conversations in the serial interface 0. Weighted fair queueing ensures that both of these IP data streams—both using TCP—receive equal bandwidth on the interface while they have messages in the pipeline, even though there is more FTP data in the queue than RCP data.

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show queueing

Router# show queueing Current fair queue configuration: Interface Serial0 Serial1 Serial2 Serial3

Discard threshold 64 64 64 64

Dynamic queue count 256 256 256 256

Reserved queue count 0 0 0 0

Current priority queue configuration: List Queue Args 1 high protocol cdp 2 medium interface Ethernet1 Current custom queue configuration: Current RED queue configuration: Interface: Ethernet3 Exp-weight-constant: 9 Class Min-th Max-th Mark-prob 0 20 40 1/10 1 22 40 1/10 2 24 40 1/10 3 26 40 1/10 4 28 40 1/10 5 31 40 1/10 6 33 40 1/10 7 35 40 1/10 rsvp 37 40 1/10

The following is sample output from the show queueing command with the red keyword specified. The output shows that the interface is configured for flow-based WRED to ensure fairness among flows in regard to packet drop. The random-detect flow average-depth-factor command was used to configure a scaling factor of 8 for this interface. The scaling factor is used to scale the number of buffers available per flow and to determine the number of packets allowed in the output queue of each active flow before the queue is susceptible to packet drop. As the output shows, the maximum flow count for this interface was set to 16 by the random-detect flow count command. Router# show queueing red Current RED queue configuration: Interface: Serial1 Exp-weight-constant: 9 Class Min-th Max-th Mark-prob 0 20 40 1/10 1 22 40 1/10 2 24 40 1/10 3 26 40 1/10 4 28 40 1/10 5 31 40 1/10 6 33 40 1/10 7 35 40 1/10 rsvp 37 40 1/10 Max flow count: 16 Average depth factor: 8

Related Commands You can use the master indexes or search online to find documentation of related commands. custom-queue-list fair-queue priority-group Flow-Based WRED 19

Command Reference

priority-list interface priority-list queue-limit queue-list interface queue-list queue byte-count random-detect random-detect flow average-depth-factor random-detect flow count show interfaces show queue

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