[opendtv] Re: Twang's Tuesday Tribune (Mark's Monday Memo)
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 6 May 2004 10:04:00 -0400
Gary Segal wrote:
> IPV6 (and IPV4 for that matter), assign IP addresses, not MAC
> address. IPV6 has a 48 bit IP address field, while IPV4 has
> a 32 bit field.
Actually, IPv6 uses 128 bit address fields. Wider than even the
MAC address is. And one option if you want to auto-configure
IPv6 addresses is to embed the MAC address of the device in the
IPv6 address. You add a prefix to the MAC address, in essence.
If you assume MAC addresses to be mostly unique, and you also
implement a duplicate address detection algorithm, you will
have a nifty way to assign IP addresses automatically, without
DHCP.
> The key difference between an IP address and an Ethernet MAC
> address is that the IP addressing systems is designed to
> support dynamic device address assignment and changes, while
> the Ethernet address system is designed to assign a permanent
> address to a physical device.
I might have said that the key difference is that IP addresses
are meant to be routable, whereas MAC addresses are just
arbitrary numbers. An IP address is more like a telephone
number, in that it is hierarchical, allowing routes to be
aggregated, so that packets can be routed to toward their
destination *intelligently*. To route based on MAC addresses
requires exhaustive lists of each address. Not very efficient.
> So, what I'm confused about is if we're discussing MAC
> addresses or IP address.
As a way of uniquely identifying destinations. Aside from
the route aggregation problem, identifying destinations
uniquely in a broadcast system seems counter-productive.
Large scale broadcast makes sense *because* individual
destinations don't need to be identified.
But I think that using MAC addresses to identify the source
does make sense. For example, using the LLC/SNAP
encapsulation option in A/90 to transmit software updates for
individual brands of DTV appliances should be very feasible.
Devices receiving these packets would ignore them if the MAC
address was for some other brand, and would give them a
closer look, and possibly run the update exe file, if the
MAC address was from the company that built the device.
Bert
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