Quality of Service Example


Defining a Quality of Service Policy for Network Traffic

Below is a map of a small corporate network. To better shape the behavior of the network loads, a Quality Of Service (QoS) policy has been created. This will allow the network administrator to regulate the amount and/or type of traffic that will pass over the weakest link on this network (The ATM link between the two switches). A QoS policy also has been helpful in restricting the users to passing only the traffic they should be passing (NFS traffic for Engineering, Database Application traffic for Accounting, etc.). This policy has to be carefully planned out; one forgotten variable could negate your whole QoS policy.


With DIGITAL products, you can have more than one QoS policy, but only one can be active at a time. This means that you can add or remove rules in a policy that is not active, review the policy for accuracy, then activate that policy by making it the default policy. Within each policy there are many rules that describe how traffic is to be categorized. These rules are kept in a list. That list is processed from the top down. You should take careful notice when entering the individual rules so as not to deny traffic to/from a source/destination before finishing with any other rules that apply to the same source/destination set.

Queuing rules and filtering rules are available in the QoS configuration. A queuing rule specifies which ATM queue to use on a per flow basis, while filtering rules deal with blocking or permitting traffic based on information in the TCP/IP header. Filters are applied using QoS Rules within a given QoS policy. As a default, when a policy is created there is a "permit all" rule in effect. That is, there is no blocking or filtering of traffic on any of the interfaces. As a general rule of thumb, when using a combination of filtering rules and QoS forwarding rules it is important to place the filtering rules at the top of the rule list. In this way, any traffic matching the filtering rule will be dropped (or filtered) prior to being tested against the QoS forwarding rule. Filtering rules are not applied across multiple QoS policies. Only the filtering rules in the currently active policy are in effect.

The Queuing Policy created has the following rules:

  1. The traffic from the 22.0/24 to the 27.0/24 network is critical and will be assigned to the highest priority. This traffic is from an accounting database program. It travels on a proprietary port number of 54376 using TCP.
  2. The traffic from 24.0/24 to the 27.0/24 network is also of critical nature and will also be assigned to the highest priority. This is primarily NFS and file sharing traffic. NFS uses UDP traffic for transport of data.
  3. The traffic from 25.0/24 to the 23.0/24 network is important, but not important enough to assign to the highest priority queue. This traffic will go into the medium queue.

The Filtering Policy created has the following rules:

  1. No filtering described in this document yet.


Half of the QoS policy needs to be configured on SW-1 and the other half of the policy configured on SW-2. This must be done because of the source and destination of the different types of traffic, some are from the right to left sides of the network and some are from left to right sides. Queue rule 1 needs to be on SW-1 but queue rule 3 needs to be implemented on SW-2. We are setting the traffic queues across the 26.68/30 network, but which side of the network the traffic is generated on and which direction it will travel must be taken into account. Having a QoS rule stating that all traffic from the 27.0/24 net to the 24.0/24 net should be of the lowest priority, and applying that rule on SW-1 will not work because the traffic must traverse the 26.68/30 net before it is set to switch at the lowest priority (it has already traveled across the switch to switch link at the normal priority).

Procedure:

Creating a QoS Policy

  1. Initiate a clearVISN IP Switch Manager session on SW-1.
  2. Click .
  3. Click the Quality of Service link in the Policy Configuration section.
  4. Click .
  5. Enter in the Policy Name edit box: qostest.

Creating a Rule for a QoS Policy

  1. On the QoS page: Click qostest in the Current QoS Policies drop-down list.
  2. Click .
  3. Click .
  4. Enter in the New Rule Name edit box: rule1. This corresponds to the rule 1 defined by the QOS policy we are going to implement.
  5. Repeat steps 3 - 4 for each rule to be created within the policy. We will create a rule 2 and on SW-2 and we will create the same policy and a rule 3.



Configuring a QoS rule using the Source or Destination IP address.

  1. Create QoS Policy. See Creating a QoS Policy.
  2. Create QoS Rule if not already done. See Creating a Rule for a QoS Policy.
  3. Edit the QoS Rule. We will show the example for rule 1 (The traffic from the 22.0/24 to the 27.0/24 network is critical and will be assigned to the highest priority. This traffic is from an accounting database program. It travels on a proprietary port number of 54376 using TCP.)
  4. Enter in the Source/MaskLen edit box: 205.226.22.0/24.
  5. Enter in the Dest/MaskLen edit box: 205.227.27.0/24.
  6. Choose the direction of the traffic that will use the rule. In other words, apply this rule to traffic either entering or leaving the interface of the IP Switch or IP Switch Gateway. The inbound or outbound direction is with respect to the IP Switch or IP Switch Gateway's ATM link not Ethernet or FDDI.
    Click the Outbound check box.
  7. (Optional) Specify the interface that will use the rule.
    Click the 26.70/30 address in the Interface drop-down list. Click .
  8. (Optional) Specify the IP Transmission layer protocol (TCP or UDP). Enter in the IPProto edit box: TCP.
  9. Specify the Filtering actions as permit for the rule. This will flag the rule as a QOS rule. Click on permit in the Filter drop-down list.
  10. Specify the priority queue to use for the rule. Click on high in the Priority drop-down list.
  11. In the IP Switch, specify whether the rule is to be implemented in the ATM switch hardware or IP Switch software. The value "switch" refers to the ATM switch hardware and "forward" refers to the IP Switch software. It is generally better to implement this rule on the IP switch and not in the software, for performance reasons. Click switch in the Forward drop-down list.
  12. Click .
  13. Repeat steps 2-12 for traffic in the reverse direction by swapping the source and destination addresses.
  14. Repeat steps 2-13 for each source destination address pair that you would like to perform a QoS operation. For Switch 1 this is rule 2.

Configuring a Qos rule using the TCP or UDP port identifier


This method gives a finer granularity to the queuing and filtering that is to be done by the QoS rules. It allows for the specific type of traffic to be filtered rather than just subnet addresses. Instead of saying that the 22.0/24 net has high priority for all traffic, we can then refine that to say only the traffic on port 54376 is eligible for the high priority queue. All other traffic on that network then takes the "normal" path if not otherwise stated.

These rules are based on the TCP or UDP port identifier. These are the well-known ports (SMTP port 25, telnet port 23, ftp port 21,22) as well as known ports that are proprietary to specific applications (In our example, the client version of the accounting software talks across the network on port 54367.)

These tasks are the same as above except for the source and destination definations. This task is being completed on Switch 1.

  1. Create QoS Policy. See Creating a QoS Policy.
  2. Create QoS Rule if not already done. See Creating a Rule for a QoS Policy.
  3. Edit the QoS Rule (rule1).
  4. Specify the source TCP or UDP port identifier. Enter in the SPort/Mask edit box: 54367. Mask is not applicable here.
  5. Specify the destination TCP or UDP port identifier. Enter in the DPort/Mask edit box: 54367. Mask is not applicable here.
  6. Choose the direction of the traffic that will utilize the rule. In other words, apply this rule to traffic entering or leaving the interface of the IP Switch or IP Switch Gateway. The Inbound or Outbound direction is with respect to the IP Switch or IP Switch Gateway. Click the Outbound check box.
  7. (Optional) Specify the interface that will use the rule.
    Click the 26.70/30 address in the Interface drop-down list. Click .
  8. (Optional) Specify the IP Transmission layer protocol (TCP or UDP). Enter in the IPProto edit box: TCP.
  9. Specify the Filtering actions as permit for the rule. This will flag the rule as a QOS rule. Click on permit in the Filter drop-down list.
  10. Specify the priority queue to use for the rule. Click on high in the Priority drop-down list.
  11. In the IP Switch, specify whether the rule is to be implemented in the ATM switch hardware or IP Switch software. The value "switch" refers to the ATM switch hardware and "forward" refers to the IP Switch software. It is generally better to implement this rule on the IP switch and not in the software, for performance reasons. Click switch in the Forward drop-down list.
  12. Click .
  13. Repeat steps 2-12 for traffic in the reverse direction by swapping the source and destination addresses.
  14. Repeat steps 2-13 for each source destination address pair that you would like to perform a QoS operation.

After completing all of the above tasks for all rules defined you will have a working QOS policy. This should be observed by network users, and server statistics. A carefully planned policy will increase your network performance and efficiency.

Copyright © 1997 Ipsilon Networks, Inc.
Portions copyright © Digital Equipment Corporation 1998. All rights reserved.
Updated January 8, 1998
Send comments to Digital Equipment Corporation, doc-quality@lkg.mts.dec.com