Performance Routing Link Groups

The Performance Routing - Link Groups feature introduced the ability to define a group of exit links as a preferred set of links, or a fallback set of links for PfR to use when optimizing traffic classes specified in an PfR policy. PfR currently selects the best link for a traffic class based on the preferences specified in a policy and the traffic class performance--using parameters such as reachability, delay, loss, jitter or MOS--on a path out of the specified link. Bandwidth utilization, cost, and the range of links can also be considered in selecting the best link. Link grouping introduces a method of specifying preferred links for one or more traffic classes in an PfR policy so that the traffic classes are routed through the best link from a list of preferred links, referred to as the primary link group. A fallback link group can also be specified in case there are no links in the primary group that satisfy the specified policy and performance requirements. If no primary group links are available, the traffic classes are routed through the best link from the fallback group. To identify the best exit, PfR probes links from both the primary and fallback groups.

Primary and fallback link groups can be configured at the master controller and are identified using a unique name. Link groups provide a method of grouping links such as high bandwidth links to be used, for example, by video traffic, by configuring an PfR policy to specify that the best link is to be selected from the link group that consists of only high bandwidth links. The traffic classes specified in a policy can be configured with only one primary link group and one fallback link group. The priority of a link group can vary between policies, a link group might be a primary link group for one policy, and a fallback link group for another policy.

See the figure below for an example of how to implement link grouping. Three link groups, ISP1, ISP2, and ISP3 represent different Internet Service Providers (ISPs) and all three ISPs have links to interfaces on the three border routers shown in the figure below. ISP1 links are the most expensive links, but they have the best Service Level Agreement (SLA) guarantees. ISP3 links are best effort links, and these links are the cheapest links. ISP2 links are not as good as the ISP1 links, but the ISP2 links are more reliable than the ISP3 links. The cost of the ISP2 links is higher than the ISP3 links, but lower than ISP1 links. In this situation, each ISP is created as a link group and associated with an interface on each border router shown in the figure below.

Figure 1

Link Group Diagram

Assuming four types of traffic class, video, voice, FTP, and data, each traffic class can be routed through a border router interface belonging to an appropriate link group. Video and voice traffic classes need the best links so the ISP1 link group is configured as the primary link group, with ISP2 as the fallback group. FTP traffic needs reliable links but the cost might be a factor so ISP2 is assigned as the primary group, and ISP3 is the fallback link group. Note that although ISP1 provides the most reliable links, it may be too expensive for file transfer traffic. For data traffic, ISP3 is a good choice as a primary link group, with ISP2 as the fallback group.

Note	If you are configuring link grouping, configure the no max-range-utilization command because using a link utilization range is not compatible with using a preferred or fallback set of exit links configured for link grouping.

Perform this task on a master controller to set up some performance routing link groups by identifying an exit link on a border router as a member of a link group, and to create a PfR map to specify link groups for traffic classes defined in a PfR policy. In this task, a link group is set up for video traffic and a set of high bandwidth exit links are identified as members of the video link group which is identified as a primary link group. A fallback link group is also specified.

A PfR policy is created using an PfR map where the primary and fall link groups are specified for traffic classes matching the PfR map criteria. PfR probes both the primary and fallback group links and selects the best link in the primary link group for the traffic class specified in this task. If none of the primary links are within policy, PfR selects the bast link from the fallback group. For more details about link groups, see the "Performance Routing Link Grouping" section.

Note	If you are configuring link grouping, configure the no max-range-utilization command because using a link utilization range is not compatible with using a preferred or fallback set of exit links configured for link grouping.

1.    enable

2.    configure terminal

3.    pfr master

4.    border ip-address [key-chain key-chain-name]

5.    interface type number external

6.    link-group link-group-name [link-group-name [link-group-name]]

7.    exit

8.    Repeat Step 5 through Step 7 with appropriate changes to set up link groups for all the external interface.

9.    interface type number internal

10.    exit

11.    ip access-list {standard | extended} access-list-name

12.    [sequence-number] permit udp source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [dscp dscp-value]

13.    Repeat Step 12 for more access list entries, as required.

14.    exit

15.    pfr-map map-name sequence-number

16.    match traffic-class access-list access-list-name

17.    set link-group link-group-name [fallback link-group-name]

18.    end

19.    show pfr master link-group [link-group-name]

Router# show pfr master link-group
link group video
  Border           Interface       Exit id 
  192.168.1.2      Serial2/0       1       
 link group voice
  Border           Interface       Exit id 
  192.168.1.2      Serial2/0       1       
  192.168.1.2      Serial3/0       2       
  192.168.3.2      Serial4/0       4       
 link group data
  Border           Interface       Exit id 
  192.168.3.2      Serial3/0       3