Subject: Re: [16NG] Review comments on draft-ietf- 16ng-ip-over-ethernet-over-802.16-00

From: "林珂" <[email-masked]>
Date: Thu, 4 Jan 2007 10:21:03 +0800 (CST)

4.4.  Discovery of MAC addresses
...
   BS can construct link local address of each SS from adding prefix
   "FE80::/64" to last 24 bits of MAC address corresponding to the each
   SS and also derive solicited-node MAC address of each SS from prefix
   "33-33-FF" and last 24 bits of each SS's MAC address.

 I think the link local address of each SS by adding prefix FE80::/64 to last 24 bits of MAC address corresponding to the each SS couldn't assure that the link-local address is unique. In addition, "33-33-FF" prefix also couldn't make MAC address unique. Is these multicast address? 

I also think link-local address is for IPv6, why should IPv4 has link-local address?
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From: Alexandru Petrescu <[email-masked]>
Date: Thu, 04 Jan 2007 18:35:30 +0100

Linke Jacob wrote:
> 4.4. Discovery of MAC addresses ... BS can construct link local 
> address of each SS from adding prefix "FE80::/64" to last 24 bits of 
> MAC address corresponding to the each SS and also derive 
> solicited-node MAC address of each SS from prefix "33-33-FF" and last
>  24 bits of each SS's MAC address.
> 
> I think the link local address of each SS by adding prefix FE80::/64 
> to last 24 bits of MAC address corresponding to the each SS couldn't 
> assure that the link-local address is unique.

That's right, I agree, should add to the IID (Interface ID) not to the
'last 24 bits'.  The IID is derived by splitting the whole 48bits,
inserting fffe somewhere and inverting a certain bit.

Or one could add only the 24bits of the MAC address but then don't call
it "IPv6 link-local address over Ethernet" because it's not.

> In addition, "33-33-FF" prefix also couldn't make MAC address unique.
>  Is these multicast address?

I guess it's the MAC-layer's 'solicited node multicast address'?

> I also think link-local address is for IPv6, why should IPv4 has 

Well, Apple (and recently Microsoft) have IPv4 link-local addresses on
their machines rfc3927.  Both IPv4 and IPv6 construct locally these
addresses (no message exchange), but an IPv6 ll address has more chances
of being unique.

That said, I do not agree with a single document IP-over-ETH covering
both IPv6 and IPv4 because the semantics are very different at the
Ethernet level.

Alex