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[ns] node address and MAC address




My problem is to implement a reliable link layer. IN order to send a  
hop-by-hop link layer ack back to the previous hop, I reverse the MacSA
and MacDA in the packet, and send it back. But this is not enough for
link layer. By reversing the macSA and macDA, the packet can reach the mac
layer of the previous node, it can NOT reach the  link layer of the
previous
node. I guess there is some kind of filter which will filter out any
packets whose dst address is diffrent from myself. So I change the dst
address in packet to the MAC address of the previous node (i do not know 
how to get the node address of previous hop node), It works when the node
address and MAC address of the nodes are the same. However, The packet
won't be able to get to the link layer if the Mac address happen to be
different from the node address..
In order to get around this,
 my question is:
1. How to get to know the node address of the previous hop node?
( I use wired LAN..)
or how to get the node address from its MAC address?

2. if I can not get the above information, can I change the node address
arbitrarily, so that the node address can be the same as the MAC address?
If I write up such a function myself to change node address, will the
change mess up the normal operation in ns, such as routing?

THanks a LOT for any feedback in advance!
yan