Filtering to classify traffic

When a packet enters the qdisc, it needs to be classified. This is done with 'tc filters', which have their own non-iptables syntax:

 # U32="tc filter add dev ppp0   \ 
    protocol ip parent 1:0 prio 1\  
    u32"
 # $U32 match ip dport 25 0xffff \ 
   flowid 1:10
 # $U32 match ip sport 80 0xffff \ 
   flowid 1:11

The u32 match is *very* generic and can match everthing. Baroque syntax, however.