Route Classifiers

Route classifiers classify the packets based on the the routing table. This involves the use of another tool, namely the IP tool (IPT). This has been described comprehensively in [2]. The syntax for creating a route classifier:

tc filter [add | del | change | get] dev STRING
	[parent PARENTID] [protocol PROTO] 
	[prio PRIORITY]  route

Where: 
PROTO = {ip | icmp | etc.}

All the fields above have already been explained. The keyword route indicates that it is a route classifier. All the packets at the specified device will be classified based on the routing table. A set of rules are specified that indicate how the packets need to be treated. This is discussed in [2].

For e.g.
To install a route classifier:

tc filter add dev eth0 parent 1:0 protocol ip prio 100 route

In the above example, a route classifier is attached to the root of a CBQ tree. The classifier will classify IP packets (as indicated by the protocol field) and the priority assigned to it 100.

To specify rules to the filter:
ip route add 129.237.125.150 via 129.237.125.146 dev eth0 flow 1:2

In this example, a route is added to 129.237.125.150 via 129.237.125.146 and all such traffic will be considered as belonging to the class whose handle is 1:2.