FRED Configuration

FRED configuration requires only slightly more effort than does WRED configuration, as long as default configuration values are acceptable. This section shows two FRED configuration examples that involve the same basic scenarios as the first two WRED examples in the previous section. FRED configuration and show commands are listed in Tables 6-11 and 6-12.

Table 6-11 Command Reference for FRED

Command

Mode and Function

random-detect flow

Interface configuration mode; enables FRED on the interface.

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

Interface configuration mode; changes scaling factor. The lower the number, the more aggressively FRED discards packets for flows using more than their fair share of the available queue space.

random-detect flow count number

Interface configuration mode; overrides default setting for the maximum number of concurrent flows tracked by FRED. (The default is 256.)

random-detect precedence precedence min-threshold max-threshold mark-prob-denominator

Interface, class, or random-detect-group configuration modes; overrides default settings for the specified precedence, for minimum and maximum WRED thresholds, and for percentage of packets discarded.

Table 6-11 Command Reference for FRED (Continued)

Command

Mode and Function

random-detect dscp dscpvalue min-threshold max-threshold [mark-pmbability-denominator]

Interface, class, or random-detect-group configuration modes; overrides default settings for the specified DSCP, for minimum and maximum WRED thresholds, and for percentage of packets discarded.

random-detect exponential-weighting-constant exponent

Interface, class, or random-detect-group configuration modes; overrides default settings for exponential weighting constant. Lower numbers make WRED react quickly to changes in queue depth; higher numbers make WRED react less quickly.

Table 6-12 Exec Command Reference for FRED

Command

Function

show queue interface-name interface-number [vc [vpi/] vci]]

Lists information about the packets that are waiting in a queue on the interface

show queueing random-detect [interface atm-subinterface [vc [[vpi/] vci]]]

Lists configuration and statistical information about the queuing tool on an interface

show interfaces

Mentions whether WRED has been enabled on the interface

show interface random-detect

Lists information about WRED when distributed WRED is running on a VIP interface

In the first example, R3 enables FRED on its S0/0 interface. FRED classifies the packets into flows and then decides which flows are currently considered to be robust, fragile, and nonadaptive. Based on the category, FRED decides whether new packets should be discarded.

This example continues the tradition of marking packets at ingress on R3's E0/0 interface. The marking logic performed by CB marking is as follows:

• HTTP traffic for web pages with "important" in the URL—DSCP AF21

• HTTP traffic for web pages with "not-so" in the URL—DSCP AF23

To generate traffic in this network, two voice calls will be made between the analog phones attached to R1 and R4. Multiple web browsers will load the standard page used in this book, with two TCP connections created by each browser—one to get a file with the word "important" in it, and the other getting a file with "not-so" in it. An FTP download of a large file will also be initiated from the Server to Clientl. Example 6-4 shows the basic configuration and show commands output. The example uses the familiar network diagram, with the configuration being added to R3.

Figure 6-12 Sample Network for All FRED Examples—Configuration on R3

Figure 6-12 Sample Network for All FRED Examples—Configuration on R3

Example 6-4 FRED Example Using All Default Values, R3 S0/0

R3#show running-config

Building configuration...

! Some lines omitted for brevity ip cef

! The following class-maps will be used for CB marking policy ! used at ingress to E0/0

class-map match-all http-impo match protocol http url "*important*" class-map match-all http-not match protocol http url "*not-so*" class-map match-all class-default match any class-map match-all voip-rtp match ip rtp 16384 16383

! The following policy-map will be used for CB marking

Example 6-4 FRED Example Using All Default Values, R3 S0/0 (Continued)

policy-map laundry-list class voip-rtp set ip dscp ef class http-impo set ip dscp af21 class http-not set ip dscp af23 class class-default set ip dscp default

call rsvp-sync

interface Ethernet0/0 description connected to SW2, where Serverl is connected ip address 192.168.3.253 255.255.255.0 ip nbar protocol-discovery half-duplex service-policy input laundry-list

interface Serial0/0 description connected to FRS port S0. Single PVC to R1. no ip address encapsulation frame-relay load-interval 30 random-detect random-detect flow clockrate 128000

interface Serial0/0.1 point-to-point description point-point subint global DLCI 103, connected via PVC to DLCI 101 ( R1)

ip address 192.168.2.253 255.255.255.0 frame-relay interface-dlci 101

Some lines omitted for brevity

R3#show queueing random-detect

Current random-detect configuration: Serial0/0

Queueing strategy: random early detection (WRED) Exp-weight-constant: 9 (1/512) Mean queue depth: 36

Max flow count: 256 Average depth factor: 4

Flows (active/max active/max): 2/8/256

class

Random drop

Tail drop

Minimum

Maximum

Mark

pkts/bytes

pkts/bytes

thresh

thresh

prob

0

25/12280

12/5651

20

40

1/10

1

0/0

0/0

22

40

1/10

2

103/125056

133/146549

24

40

1/10

3

0/0

0/0

26

40

1/10

Example 6-4 FRED Example Using All Default Values, R3 S0/0 (Continued)

4

0/0

0/0

28

40

1/10

5

641/41024

1475/94400

31

40

1/10

6

0/0

0/0

33

40

1/10

7

0/0

0/0

35

40

1/10

rsvp

0/0

0/0

37

40

1/10

The FRED part of the configuration is again quite short. The configuration lists the random-detect interface subcommand under serial 0/0, which enables precedence-based WRED on the interface. Because FRED is actually a superset of WRED, you also need to add the random-detect flow command to the interface. Interestingly, IOS adds the random-detect command to the interface if you only type the random-detect flow command. The rest of the detailed configuration in this example is just like the first WRED example configuration, repeating the CB marking configuration that marks the VoIP, FTP, and two different types of HTTP traffic. (For more information about CB marking, see Chapter 3.)

The only command that lists any new information, as compared with WRED, is the show queueing random-detect interface serial 0/0 command. Most of the output looks familiar: It includes the various IP precedence values, with statistics. Just like with WRED, the command lists per-precedence default values for minimum threshold and maximum threshold. FRED still uses these values when determining the percentage of packets to discard. Specifically new for FRED, the command output lists two values used by the FRED algorithm when deciding to discard packets, namely the maximum flow count and average depth factor. The maximum flow count is the maximum number of unique active flows tracked by FRED. The average depth factor describes the scaling factor as described in the FRED concepts section, used when calculating the maximum per-flow queue size.

Although FRED does track and act on flow information, listing statistics per flow would be cumbersome, because the flows may well be short lived. The show queueing command still lists statistics, but it groups the statistics based on the precedence value (or DSCP value if DSCP-based FRED is used).

The second FRED configuration example uses FRED on the interface again, but this time with DSCP FRED, and a few defaults changed. In fact, Example 6-5 just shows the changed configuration, with most of the configuration staying the same. The same CB marking configuration is used to mark the traffic, for instance, so the details are not repeated in the example. The example uses the familiar network diagram used in Example 6-4.

Example 6-5 DSCP-BasedFRED on R3 S0/0

R3#conf t

Enter configuration commands, one per line. End with CNTL/Z. R3(config)#interface serial 0/0 R3(config-if)#random-detect flow ?

average-depth-factor Average depth multiplier (1, 2, 4, 8 or 16)

Example 6-5 DSCP-BasedFRED on R3 S0/0 (Continued)

count max number of dynamic flows

R3(config-if)#random-detect flow average-depth-factor 2 R3(config-if)#random-detect flow count 19

Number of WRED flows must be a power of 2 (16, 32, 64, 128, 256, 512, 1024

2048, 4096, 8192, 16384 or 32768) R3(config-if)#random-detect flow count 64 R3(config-if)#~Z R3#

R3#show queueing random-detect

Current random-detect configuration: Serial0/0

Queueing strategy: random early detection (WRED) Exp-weight-constant: 9 (1/512) Mean queue depth: 39

Max flow count: 64 Average depth factor: 2 Flows (active/max active/max): 13/13/64

dscp

Random drop Tail drop

Minimum

Maximum

Mark

pkts/bytes pkts/bytes

thresh

thresh

prob

af11

0/0 0/0

33

40

1/10

af12

0/0 0/0

28

40

1/10

af13

0/0 0/0

24

40

1/10

af21

19/23334 1/1404

33

40

1/10

af22

0/0 0/0

28

40

1/10

af23

11/14116 0/0

24

40

1/10

af31

0/0 0/0

33

40

1/10

af32

0/0 0/0

28

40

1/10

af33

0/0 0/0

24

40

1/10

af41

0/0 0/0

33

40

1/10

af42

0/0 0/0

28

40

1/10

af43

0/0 0/0

24

40

1/10

cs1

0/0 0/0

22

40

1/10

cs2

0/0 0/0

24

40

1/10

cs3

0/0 0/0

26

40

1/10

cs4

0/0 0/0

28

40

1/10

cs5

0/0 0/0

31

40

1/10

cs6

0/0 0/0

33

40

1/10

cs7

0/0 0/0

35

40

1/10

ef

11/704 2658/170112

37

40

1/10

rsvp

0/0 0/0

37

40

1/10

default

7/7396 16/14275

20

40

1/10

The configuration begins with a change from precedence-based FRED to DSCP-based FRED using the random-detect dscp-based interface subcommand. (The configuration already contained the random-detect flow command to enable flow-based WRED.) Two FRED options can be set with the random-detect flow command, as seen in the example. The average depth factor defines the multiple of the average queue space per flow that can be allocated to a single flow before FRED decides to start discarding packets. (Formula: average depth factor * maximum queue depth / number of active flows) The flow count, set to 64 in this example, just sets the maximum number of unique flows tracked by FRED. Just like with WFQ, the setting of the number of flows must be set to a power of 2.

Just like with DSCP-based WRED, the command output for DSCP-based FRED does not differ from the earlier precedence-based FRED example in too many ways. The changes to the default values have been highlighted in the example. The show queueing command contains the only notable difference between the command outputs in the first two examples, now listing information about all the DSCP values recommended in the DSCP RFCs. Notice that the counters point out drops for both AF21 and AF23, which were previously both treated as precedence 2 by precedence-based FRED. Also note that FRED has discarded some voice traffic (DSCP EF) in this example. Because FRED operates on all traffic in the interface FIFO queue, it cannot avoid the possibility of discarding voice traffic.

Table 6-13 summarizes many of the key concepts when comparing WRED and FRED.

Table 6-13 WRED Versus FRED

Table 6-13 summarizes many of the key concepts when comparing WRED and FRED.

Table 6-13 WRED Versus FRED

Feature

WRED

FRED

Discards packets to avoid congestion

Yes

Yes

Can be enabled on the physical interface concurrently with a queuing tool

No

No

Can be combined with CBWFQ or LLQ policy map

Yes

No

Bases drop decision, at least in part, on different thresholds per precedence or DSCP value

Yes

Yes

Bases drop decision, at least in part, on per-flow queue depth

No

Yes

Advance SEO Techniques

Advance SEO Techniques

Turbocharge Your Traffic And Profits On Auto-Pilot. Would you like to watch visitors flood into your websites by the 1,000s, without expensive advertising or promotions? The fact is, there ARE people with websites doing exactly that right now. How is that possible, you ask? The answer is Advanced SEO Techniques.

Get My Free Ebook


Post a comment