- Cisco IOS Release 12.0 Quality of Service Solutions Configuration Guide
Table Of Contents
Configuring Weighted Random Early Detection
Weighted Random Early Detection Configuration Task List
WRED and DWRED Configuration Examples
DWRED and WRED Configuration Example
Parameter-Setting DWRED Example
Parameter-Setting WRED Example
Configuring Weighted Random Early Detection
This chapter describes the tasks for configuring Weighted Random Early Detection (WRED) and Distributed WRED (DWRED) on a router. For a complete description of the commands mentioned in this chapter, refer to the Quality of Service Solutions Command Reference; the commands are listed alphabetically within that guide. To locate documentation of specific commands, use the command reference, master index, or search online.
The WRED feature is supported on these Cisco router platforms:
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Cisco 1600 series
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The DWRED feature is only supported on Cisco 7000 series routers with a Route Switch Processor-based RSP7000 interface processor and Cisco 7500 series routers with a Versatile Interface Processor-based VIP2-40 or greater interface processor. A VIP2-50 interface processor is strongly recommended when the aggregate line rate of the port adapters on the VIP is greater than DS3. A VIP2-50 interface processor is required for OC-3 rates. To use DWRED, Distributed Cisco Express Forwarding (DCEF) switching must first be enabled on the interface. For more information on DCEF, refer to the Cisco IOS Switching Services Configuration Guide and the Cisco IOS Switching Services Command Reference.
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WRED treats non-IP traffic as precedence 0, the lowest precedence. Therefore, non-IP traffic is more likely to be dropped than IP traffic.
You cannot configure WRED on the same interface as Route Switch Processor (RSP)-based custom queueing, priority queueing, or weighted fair queueing (WFQ). However, you can configure both DWRED and DWFQ on the same interface.Weighted Random Early Detection Configuration Task List
Random Early Detection (RED) is a congestion avoidance mechanism that takes advantage of TCP's congestion control mechanism. By randomly dropping packets prior to periods of high congestion, RED tells the packet source to decrease its transmission rate. WRED drops packets selectively based on IP Precedence. Edge routers assign IP Precedences to packets as they enter the network. WRED is useful on any output interface where you expect to have congestion. However, WRED is usually used in the core routers of a network, rather than the edge. WRED uses these precedences to determine how it treats different types of traffic.
When a packet arrives, the following events occur:
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See the section "About Weighted Random Early Detection" in the chapter "Congestion Avoidance Overview" in this book for more details on the queue calculations and how WRED works.
To configure WRED or DWRED on an interface, perform the tasks in the following sections:
The section "WRED and DWRED Configuration Examples" later in this chapter provides examples of configuring WRED.
Enable WRED
To enable WRED, use the following command in interface configuration mode:
random-detect
Enable WRED. If you configure this command on a VIP interface, DWRED is enabled.
You need not specify any other commands or parameters in order to configure WRED on the interface. WRED will use the default parameter values.
Change WRED Parameters
To change WRED parameters, use one of the following commands in interface configuration mode:
When you enable WRED with the random-detect command, the parameters are set to their default values. The weight factor is 9. For all precedences, the mark probability denominator is 10, and maximum threshold is based on the output buffering capacity and the transmission speed for the interface.
The default minimum threshold depends on the precedence. The minimum threshold for IP Precedence 0 corresponds to half of the maximum threshold. The values for the remaining precedences fall between half the maximum threshold and the maximum threshold at evenly spaced intervals.
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Monitor WRED and DWRED
To monitor WRED services in your network, use any of the following commands in EXEC mode:
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WRED and DWRED Configuration Examples
The following sections provide these examples:
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DWRED and WRED Configuration Example
The following example enables WRED or DWRED with default parameter values:
router(config)# interface Serial5/0router(config-if)# description to qos1-75arouter(config-if)# ip address 200.200.14.250 255.255.255.252router(config-if)# random-detectUse the show interfaces command output to verify the configuration and view the default settings for the different precedences. Notice that the "Queueing strategy" report lists "random early detection (RED)." Also notice that the default minimum thresholds are spaced evenly between half and the entire maximum threshold. Thresholds are specified in terms of packet count.
router# show interfaces serial 5/0Serial5/0 is up, line protocol is upHardware is M4TDescription: to qos1-75aInternet address is 200.200.14.250/30MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,reliability 255/255, txload 1/255, rxload 237/255Encapsulation HDLC, crc 16, loopback not setKeepalive not setLast input 00:00:15, output 00:00:00, output hang neverLast clearing of "show interface" counters 00:05:08Input queue: 0/75/0 (size/max/drops); Total output drops: 1036Queueing strategy: random early detection(RED)mean queue depth: 28drops: class random tail min-th max-th mark-prob0 330 0 20 40 1/101 267 0 22 40 1/102 217 0 24 40 1/103 156 0 26 40 1/104 61 0 28 40 1/105 6 0 31 40 1/106 0 0 33 40 1/107 0 0 35 40 1/10rsvp 0 0 37 40 1/1030 second input rate 0 bits/sec, 2 packets/sec30 second output rate 119000 bits/sec, 126 packets/sec594 packets input, 37115 bytes, 0 no bufferReceived 5 broadcasts, 0 runts, 0 giants, 0 throttles0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort37525 packets output, 4428684 bytes, 0 underruns0 output errors, 0 collisions, 0 interface resets0 output buffer failures, 0 output buffers swapped out0 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=upUse the show queue command output to view the current contents of the interface queue. Notice that there is only a single queue into which packets from all IP precedences are placed after dropping has taken place.
router# show queue serial 5/0Output queue for Serial5/0 is 5/0Packet 1, linktype: ip, length: 118, flags: 0x288source: 190.1.3.4, destination: 190.1.2.2, id: 0x0001, ttl: 254,TOS: 128 prot: 17, source port 11111, destination port 22222data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x43210x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765Packet 2, linktype: ip, length: 118, flags: 0x288source: 190.1.3.5, destination: 190.1.2.2, id: 0x0001, ttl: 254,TOS: 160 prot: 17, source port 11111, destination port 22222data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x43210x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765Packet 3, linktype: ip, length: 118, flags: 0x280source: 190.1.3.6, destination: 190.1.2.2, id: 0x0001, ttl: 254,TOS: 192 prot: 17, source port 11111, destination port 22222data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x43210x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765Packet 4, linktype: ip, length: 118, flags: 0x280source: 190.1.3.7, destination: 190.1.2.2, id: 0x0001, ttl: 254,TOS: 224 prot: 17, source port 11111, destination port 22222data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x43210x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765Packet 5, linktype: ip, length: 118, flags: 0x280source: 190.1.3.8, destination: 190.1.2.2, id: 0x0001, ttl: 254,TOS: 0 prot: 17, source port 11111, destination port 22222data: 0x2B67 0x56CE 0x005E 0xE89A 0xCBA9 0x8765 0x43210x0FED 0xCBA9 0x8765 0x4321 0x0FED 0xCBA9 0x8765Use the show queueing command output to view the current settings for each of the precedences.
router# show queueingCurrent RED queue configuration:Interface: Serial5/0 Exp-weight-constant: 9Class Min-th Max-th Mark-prob0 20 40 1/101 22 40 1/102 24 40 1/103 26 40 1/104 28 40 1/105 31 40 1/106 33 40 1/107 35 40 1/10rsvp 37 40 1/10Parameter-Setting DWRED Example
The following example specifies the same parameters for each IP Precedence. Thus, all IP precedences receive the same treatment. Start by enabling DWRED.
router(config)# interface FastEthernet1/0/0router(config-if)# ip address 200.200.14.250 255.255.255.252router(config-if)# random-detectNext, use the show interfaces random-detect command to determine reasonable values to use for the precedence-specific parameters:
router# show interfaces random-detectFastEthernet1/0/0 queue size 0packets output 29692, drops 0WRED: queue average 0weight 1/512Precedence 0: 109 min threshold, 218 max threshold, 1/10 mark weight1 packets output, drops: 0 random, 0 thresholdPrecedence 1: 122 min threshold, 218 max threshold, 1/10 mark weight(no traffic)Precedence 2: 135 min threshold, 218 max threshold, 1/10 mark weight14845 packets output, drops: 0 random, 0 thresholdPrecedence 3: 148 min threshold, 218 max threshold, 1/10 mark weight(no traffic)Precedence 4: 161 min threshold, 218 max threshold, 1/10 mark weight(no traffic)Precedence 5: 174 min threshold, 218 max threshold, 1/10 mark weight(no traffic)Precedence 6: 187 min threshold, 218 max threshold, 1/10 mark weight14846 packets output, drops: 0 random, 0 thresholdPrecedence 7: 200 min threshold, 218 max threshold, 1/10 mark weight(no traffic)
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Complete the configuration by assigning the same parameter values to each precedence. Use the values obtained from the show interfaces random-detect command output to choose reasonable parameter values.
router(config)# interface FastEthernet1/0/0router(config-if)# random-detect precedence 0 100 218 10router(config-if)# random-detect precedence 1 100 218 10router(config-if)# random-detect precedence 2 100 218 10router(config-if)# random-detect precedence 3 100 218 10router(config-if)# random-detect precedence 4 100 218 10router(config-if)# random-detect precedence 5 100 218 10router(config-if)# random-detect precedence 6 100 218 10router(config-if)# random-detect precedence 7 100 218 10Parameter-Setting WRED Example
The following example enables WRED on the interface and specifies parameters for the different IP precedences:
router(config)# interface Hssi0/0/0router(config-if)# description 45Mbps to R1router(config-if)# ip address 200.200.14.250 255.255.255.252router(config-if)# random-detectrouter(config-if)# random-detect precedence 0 32 256 100router(config-if)# random-detect precedence 1 64 256 100router(config-if)# random-detect precedence 2 96 256 100router(config-if)# random-detect precedence 3 120 256 100router(config-if)# random-detect precedence 4 140 256 100router(config-if)# random-detect precedence 5 170 256 100router(config-if)# random-detect precedence 6 290 256 100router(config-if)# random-detect precedence 7 210 256 100router(config-if)# random-detect precedence rsvp 230 256 100
