where to add marker for packets

[Urs Thuermann <thuerman@ibr.cs.tu-bs.de>]

I want to add an instance to some nodes in a ns-2 simulation that is
able to mark packets depending on src and dst addresses and/or type of
the packet.

I have 2 questions on this:

1. What field in the packet is appropriate to do the marking?  Should
   I define a new packet type containing a field for the mark or can I
   use some existing field.  One byte would be enough for my purposes.

2. How should implement the marker and how install it at the node?  I
   think it should be a descendant of the Connector class and be
   inserted between the node's entry and the classifier.  Or is there
   a better way?

   I think of writing a Tcl proc that creates a new node, creates and
   instance of the marker, sets the target_ of the marker to the
   node's entry{} and then sets the node's entry{} to point to the
   marker.  Any thoughts on this?

TIA

urs