How to Configure Forwarding for Application Traffic in the IPQoS Configuration File

The next procedure shows how to configure forwarding for application traffic. In the procedure, you define per-hop behaviors for application traffic classes that might have lower precedence than other traffic on a network. The procedure assumes that you have an existing IPQoS configuration file with already-defined classes and filters for the applications to be marked. The steps continue building the /var/ipqos/BigAPPs.qos file in Example 3–3.

1. Open the IPQoS configuration file you have created for the applications server.

   Locate the end of the last filter clause. In the /var/ipqos/BigAPPs.qos file, the last filter is the following:

   filter { name ftpdata sport ftp-data class ftp } }

2. Invoke the marker as follows:

   action { module dscpmk name markAF13

   Entry	Description
   module dscpmk	Invokes the marker module dscpmk
   name markAF13	Gives the name markAF13 to the action statement

3. Define the per-hop behavior to be marked on electronic mail traffic flows.

   params { global_stats FALSE dscp_map{0-63:14} next_action continue } }

   Entry	Description
   global_stats FALSE	Enables statistics taking for the markAF13 marker action statement. However, because the value of enable_stats is FALSE, statistics are not turned on.
   dscp_map{0–63:14}	Assigns a DS codepoint of 14 to the packet headers of the traffic class smtp, which is currently being processed by the marker.
   next_action continue	Indicates that no further processing is required on packets of the traffic class smtp. These packets can then return to the network stream.

   The DS codepoint 14 tells the marker to set all entries in the dscp map to the decimal value 14 (binary 001110). This value sets the AF13 per-hop behavior and marks packets of the smtp traffic class with the DS codepoint 14 in the DS field.

   AF13 assigns all packets with a DS codepoint of 14 to a high-drop precedence. However, because AF13 also assures a Class 1 priority, the router still guarantees outgoing email traffic a high priority in its queue. For a table of possible AF codepoints, refer to Table 6–2.

4. Add a marker action statement to define a per-hop behavior for network news traffic:

   action { module dscpmk name markAF21 params { global_stats FALSE dscp_map{0-63:18} next_action continue } }

   The next table explains parameters that have not yet been defined in this procedure.

   Entry	Description
   name markAF21	Gives the name markAF21 to the action statement
   dscp_map{0–63:18}	Assigns a DS codepoint of 18 to the packet headers of the traffic class nntp, which is currently being processed by the marker

   The DS codepoint 18 tells the marker to set all entries in the dscp map to the decimal value 18 (binary 010010). This value sets the AF21 per-hop behavior and marks packets of the news traffic class with the DS codepoint 18 in the DS field.

   AF21 assures that all packets with a DS codepoint of 18 receive a low-drop precedence, but with only Class 2 priority. Thus, the possibility of network news traffic being dropped is low, but the router gives a higher forwarding probability to traffic classes with a Class 1 mark.

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