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Configuring RED Drop Profiles for Congestion Control

If the device must support assured forwarding, you can control congestion by configuring random early detection (RED) drop profiles. RED drop profiles use drop probabilities for different levels of buffer fullness to determine which scheduling queue on the device is likely to drop assured forwarding packets under congested conditions. The device can drop packets when the queue buffer becomes filled to the configured percentage.

Assured forwarding traffic with the PLP (packet loss priority) bit set is more likely to be discarded than traffic without the PLP bit set. This example shows how to configure a drop probability and a queue fill level for both PLP and non-PLP assured forwarding traffic. It is only one example of how to use RED drop profiles.

The example shows how to configure the RED drop profiles listed in Table 201.

Table 201: Sample RED Drop Profiles

Drop Profile

Drop Probability

Queue Fill Level

af-normal—For non-PLP (normal) assured forwarding traffic

Between 0 (never dropped) and 100 percent (always dropped)

Between 95 and 100 percent

af-with-plp—For PLP (aggressive packet dropping) assured forwarding traffic

Between 95 and 100 percent (always dropped)

Between 80 and 95 percent

To configure RED drop profiles for assured forwarding congestion control on the device:

  1. Navigate to the top of the configuration hierarchy in either the J-Web or CLI configuration editor.
  2. Perform the configuration tasks described in Table 202.
  3. If you are finished configuring the device, commit the configuration.
  4. Go on to one of the following tasks:

Table 202: Configuring RED Drop Profiles for Assured Forwarding Congestion Control

Task

J-Web Configuration Editor

CLI Configuration Editor

Navigate to the Class of service level in the configuration hierarchy.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Class of service, click Configure or Edit.

From the [edit] hierarchy level, enter

edit class-of-service

Configure the lower drop probability for normal, non-PLP traffic.
  1. Click Add new entry next to Drop profiles.
  2. In the Profile name box, type the name of the drop profile—for example, af-normal.
  3. Click Configure next to Interpolate.
  4. Click Add new entry next to Drop probability.
  5. In the Value box, type a number for the first drop point—for example, 0.
  6. Click OK.
  7. Click Add new entry next to Drop probability again.
  8. In the Value box, type a number for the next drop point—for example, 100.
  9. Click OK.

Enter

edit drop-profiles af-normal interpolate

set drop-probability 0

set drop-probability 100

Configure a queue fill level for the lower non-PLP drop probability.
  1. Click Add new entry next to Fill level.
  2. In the Value box, type a number for the first fill level—for example, 95.
  3. Click OK.
  4. Click Add new entry next to Fill level.
  5. In the Value box, type a number for the next fill level—for example, 100.
  6. Click OK three times.

Enter

set fill-level 95

set fill-level 100

Configure the higher drop probability for PLP traffic.
  1. Click Add new entry next to Drop profiles.
  2. In the Profile name box, type the name of the drop profile—for example, af-with-plp.
  3. Click Configure next to Interpolate.
  4. Click Add new entry next to Drop probability.
  5. In the Value box, type a number for the first drop point—for example, 95.
  6. Click OK.
  7. Click Add new entry next to Drop probability.
  8. In the Value box, type a number for the next drop point—for example, 100.
  9. Click OK.

From the [edit class of service] hierarchy level, enter

edit drop-profiles af-with-PLP interpolate

set drop-probability 95

set drop-probability 100

Configure a queue fill level for the higher PLP drop probability.
  1. Click Add new entry next to Fill level.
  2. In the Value box, type a number for the first fill level—for example, 80.
  3. Click OK.
  4. Click Add new entry next to Fill level.
  5. In the Value box, type a number for the next fill level—for example, 95.
  6. Click OK.

Enter

set fill-level 80

set fill-level 95

Example: Configuring RED Drop Profiles

Create a segmented configuration and an interpolated configuration that correspond to the graphs in Figure 91. The values defined in the configuration are matched to represent the data points in the graph line. In this example, the drop probability is 25 percent when the queue is 50 percent full. The drop probability increases to 50 percent when the queue is 75 percent full.

Figure 91: Segmented and Interpolated Drop Profiles

Image h1704.gif

Segmented

class-of-service {
drop-profiles {
segmented-style-profile {
fill-level 25 drop-probability 25;
fill-level 50 drop-probability 50;
fill-level 75 drop-probability 75;
fill-level 95 drop-probability 100;
}
}
}

To create the profile’s graph line, the software begins at the bottom-left corner, representing a 0 percent fill level and a 0 percent drop probability. This configuration draws a line directly to the right until it reaches the first defined fill level, 25 percent for this configuration. The software then continues the line vertically until the first drop probability is reached. This process is repeated for all of the defined levels and probabilities until the top-right corner of the graph is reached.

Create a smoother graph line by configuring the profile with the interpolate statement. This allows the software to automatically generate 64 data points on the graph beginning at (0, 0) and ending at (100, 100). Along the way, the graph line intersects specific data points, which you define as follows:

Interpolated

class-of-service {
drop-profiles {
interpolated-style-profile {
interpolate {
fill-level [ 50 75 ];
drop-probability [ 25 50 ];
}
}
}
}
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