3600 Flow-Based WRED

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Flow-Based WRED 1

Flow-Based WRED

Feature SummaryFlow-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:

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

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

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

Because of its packet-drop behaviorthat is, that all flows, even those with relatively fewer packets

in the output queue, are susceptible to packet drop during periods of congestionWRED tends

toward bias against fragile flows.Thoughfragile flows have fewerbuffered packets, they aredropped

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 sourceaddresses and ports.

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.


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Platforms

2 Cisco IOS Release 12.0(3)T

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.

RestrictionsWRED, 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.

PlatformsThe 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.

PrerequisitesPerform the following tasks before you configure flow-based WRED:

Enable WRED, using the random-detect command.

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

Optionally, configure parameters for packets with a specific IP Precedence using therandom-detect precedence 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 RFCsNone.


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Restrictions

Flow-Based WRED 3

Configuration TaskBefore 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:

Configuration ExamplesThefollowing example enables Weighted RandomEarly Detection(WRED) on theSerial1 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.

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.


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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 Ethernet0no ip address

no ip directed-broadcast

no ip mroute-cache

shutdown

!

interface Serial0

no ip address


no ip mroute-cache

no keepalive

shutdown

!

interface Serial1

ip address 190.1.2.1 255.255.255.0


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

Flow-Based WRED 5

!

line con 0

transport input none

line 1 16

transport input all

line aux 0

transport input allline vty 0 4

password lab

login

!

end


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Command Reference


Command ReferenceThis section documents new or modified commands. All other commands used with this feature are

documented in the Cisco IOS Release 12.0 command references.

random-detect flow

random-detect flow average-depth-factor

random-detect flow count

show interfaces

show queue

show queueing


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random-detect flow

Flow-Based WRED 7

random-detect flowTo 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 precedenceshow interfaces

show queue

show queueing


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Command Reference


random-detect flow average-depth-factorTo 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

Default

4

Command Mode


Usage Guidelines


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 scalednumber 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 nonadaptivethat is, it takes up too much of the resourceswhen the average

flow depth times the specified multiplier (scaling factor) is less than the flows depth, that is:

average-flow-depth * (scaling factor) < flow-depth

Beforeyou 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-if)# random-detect flow average-depth-factor 8

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


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Flow-Based WRED 9

Related Commands


random-detect flow


random-detect precedence

show interfaces

show queue

show queueing


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Command Reference


random-detect flow countTo 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 numberno random-detect flow count number

Syntax Description

Default

256

Command Mode


Usage Guidelines


Beforeyou 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-if)# random-detect flow count 16

Related Commands


random-detect flow

random-detect precedence

show interfaces

show queueshow queueing

number Specify a value from 0 to 215.


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show interfaces

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show interfacesTo 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 theCisco 7500 series routers)

Syntax Description

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.

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.


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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-prob0 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

Flow-Based WRED 13

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)


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


Received 0 broadcasts, 0 runts, 0 giants


0 watchdog, 0 multicast

0 input packets with dribble condition detected


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


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


Received 1577 broadcasts, 0 runts, 0 giants

0 parity



0 output errors, 0 applique, 3 interface resets

0 output buffers copied, 0 interrupts, 0 failures


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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



show queueing


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show queue

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show queueTo 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

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

interface-type The name of the interface.

interface-number The number of the interface.

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.


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Command Reference


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..

destination Destination IP address

id Packet ID.

ttl Time to live count.

prot Layer 4 protocol number.

data Packet data.

Table 2 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.

Field Description


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show queue

Flow-Based WRED 17

Related Commands

custom-queue-list

fair-queue

priority-group



queue-list interfacequeue-list queue byte-count

random-detect



show interfaces

show queueing

destination Destination IP address.

id Packet ID.

ttl Time to live count.

TOS IP type of service.

prot Layer 4 protocol number.

Table 2 Show Queue Field Descriptions (Continued)for WFQ

Field Description


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Command Reference


show queueingTo list all or selected configured queueing strategies, use the show queueing privileged EXEC

command.

show queueing [custom | fair | priority | red]

Syntax Description

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 Queue Args

3 10 default

3 3 interface Tunnel3

3 3 protocol ip

3 3 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 datastreamsboth using TCPreceive 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.

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.


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show queueing

Flow-Based WRED 19

Router# show queueing

Current fair queue configuration:

Interface Discard Dynamic Reservedthreshold queue count queue count

Serial0 64 256 0

Serial1 64 256 0

Serial2 64 256 0

Serial3 64 256 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 ofbuffers 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 1/107 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


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Command Reference



queue-list interface

queue-list queue byte-count

random-detect

random-detect flow average-depth-factorrandom-detect flow count

show interfaces

show queue

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3600 Flow-Based WRED

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