Subject: comments and ideas .

From: Morcos G Mikhail <[email-masked]>
Date: Fri, 12 Jul 2002 14:32:57 +0100

Hi all ,
	I have some comments and ideas I want to discuss with you :

1- In the draft it is mentiond that if a host sees 2 conflicting arp
packets carrying its IP then it must cease using this IP and starts
using another one , this is simply a good way for attacking a zeroconf
network .. just issue 2 conflicting arp packets within 1 sec for a
certian host and it is down ??

2- For hosts that have different link-local address for different
interfaces [sec 3.3.2 in the draft] the out going packets must be
identified by the source and destination address and port numbers ,not
just by the destination address and port number alone . This imposes
some difficulties for the implementations of zerconf protocol because it
forces the host that has multiple interfaces to work similar to a
router, because the host has to remember the interface from which
packets arrive and it has to answer this packet through the same
interface and so on ..

4- All hosts has to process each arp request or reply and compare it
with its IP address to detect conflicts and this may imposes some delays
   on the Pcs performance .

3- Why don't we use rarp instead of arp for allocating an IP address ,
and here how it goes :        
	
        a- Any host that needs an IP address sends a rarp packet
requesting and IP and this is by default broadcasted

	b- Upon recieving the rarp request packet all hosts respond by sending
a series of rarp replies the first one contains their IP 	          
address and the rest contains all the IP address that are in their cache

        c- When a host recieves all this replies it has to choose an IP
address which is not sent to it .

This approach has many advantages :

1- The number of broadcast packets is less , just 1 broadcast for the
rarp request and all the rarp replies will be unicasted [by default] .

2- No changes in the packet format of the rarp protocol.

3- Upon recieving a rarp request the zerconf protocol implmentation may
alret the users and ask them to either accept the new host in
their       network or not and here network attacks become less  .

4- The host that initiated the rarp request will have all the IPs and
physical address of the neighbouring Pcs .

5- With this kind of information and the fact that the IP is choosen
Randomly using the hardware address of the network interface card   
the    propability to choose a conflicting IP becomes less .

6- For hosts that have different interfaces on different links ,these
hosts issue rarp request on all the links that they are connected to
and    upon recieving the replies they will choose IPs that are
completely differnet form the IPs that are already in use on both links
and this  
   and this removes the address reuse ambiguity .

7- The hosts that fails or busy to respond its IP address is most likely
stored on any of the caches of other hosts and it will be sent to the
   host that requested an IP address so the propability to choose a
conflicting IP address becomes less .

8- For security issues , hosts must not respond to rarp requests that is
initiated from the same Hardware Address within a certain period        
of time [to be calculated so that no flooding happens to the network ] .

Best regards , 
                                                                                
Morcos George mikhail 
                                                                                
Msc. researcher
                                                                                
Faculty of Computer Since and Informatin Technology 
                                                                                
Nottingham Univesrity 
                                                                                
England .