Hi,
Packet filtering though it seems to be easy is one of the most studied
topics in networking..and there are many papers to support this. Look at
1. http://www.acm.org/sigcomm/sigcomm98/tp/abs_17.html
2. http://www.cdt.luth.se/~olov/publications/IWQoS-99b.pdf
hth,
Arni
Christian Worm Mortensen wrote:
>
> Hi,
>
> Is there any documentation about the u32 classifiers except for the
> source code? The exampels I have seen on it's usage (for example in
> the paper "Quality of Service Support in Linux" by "Saravanan
> Radhakrishnan") really looks like magic to me. As far as I have understood
> a filter should do the following:
>
> 1) Look at the packet
> 2) Tell the qdisc it belongs to in which of it's classes it should put the
> packet.
>
> That is, it should be a mapping from packets to class ids. That sounds
> easy enough... As I can figure out u32 makes it possible to setup a rule
> for each class. That is, you can say, for example, that packets to this
> and this IP address should go to this class, packets from that and that
> TCP port should go to that class and so on.
>
> Okay, that sounds just fine. But how does it work and how do I specify it?
> I understand that u32 somehow uses a hash-tables and that I need to set
> that one up. It is, however, not obvious to me how a hash table can be
> used to solve this problem.
>
> At the first glance one might thing that a hash-key is calculated from
> the packet and then looked up in the hash table which then contains the
> class that the packet should go to (or a list of possible classes). But
> this is not possible because which parts of the packets that should
> contribute to such a hashkey will be different for the different classes
> (depending on weather it describes source IP or destination TCP port,
> for example).
>
> So what is the point? If someone can describe it so that I can understand
> it I will be happy to make a general user-friendly description on how to
> setup trafic-control. I think I already have understood alot of how the
> trafic control works and I have written my own qdisc which also contains
> classes that can be manipulated with tc. But it uses it's own build-in
> filter.
>
> Christian
>
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