Chapter 4. Packet Tagging

The Scout module tags every outgoing packet with the ID of the sending slice, by placing the slice ID in the nfmark field of the sk_buff containing the packet. This tag is used by the Hierarchical Token Bucket traffic controller to assign the packet to the correct token bucket; currently, each slice with an ID of at least 500 has its own token bucket, and packets sent by other users end up in the "default" bucket. A limitation of this approach is that other modules that use the netfilter interface (e.g., iptables) could try to write to the nfmark field as well; currently, no such conflicts are known in PlanetLab.