Subject: Re: An approach for detachable interfaces.
To: Bill Sommerfeld <>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
List: tech-net
Date: 11/05/1999 12:30:55
In message <>,
Bill Sommerfeld writes:
>     what an interface *is*: e.g.,  the first ne2k on a system,
>     or a specific ne2k card and MAC address?
>There are signficant reasons to want to support a "reattach" model
>which allows the MAC address to change.  For instance, consider the
>"hot swap" case on a high-availability system, where an interface
>fails, is unplugged, and a new card (with a different MAC address) is
>hot-plugged in its place.

I have two cards from the same manufacturer. One at home and one at
work. They have different MAC addresess.  They have different IP
addresses.  An approach which attaches one card as the same device as
the other card *by default*, (if I insert one after both were removed)
is broken, period.  The way I read your proposal, that's what you're


>IMHO, the relevant event here is *not* reappearance of the hardware,
>but rather reappearance of "carrier" on the LAN medium, indicating
>that the net's been plugged back in (with the 802.11 cards i'm playing
>with, it seems to take multiple seconds to reacquire an access point).

I think you're missing my point. I'm not talking about 802.11 cards,
or about acquisition of carrier sense. The first thing I askedwas
when, in your proposal, two cards are ``the same'', and when they're

Forget about 802.11 altogether for the moment, and think what you
propposed would work with wired Ethernet cards in the scenarios I
	a) roaming with one card around multiple subnets

	b) romaing around multiple subnets, using multiple
	   cards each of which stays at the same subnet
	  and has a static (or long-lived dynamic) address.