laptop internet addresses

[der Mouse]

In article <27035 at adm.brl.mil>, ketell at mercury (Gregory Ketell) writes:
>> Laptop PC's and Unix boxes will be upon all us administrators soon.
>> Complete with Ethernet interfaces.  My question: how do you assign
>> Internet addresses to people who may plug into different subnets on
>> different days ?  If you give them multiple addresses you could eat
>> up a lot of address space in a hurry ?

> I may catch a lot of flak from the Gurus but here is my view:

> Why bother giving them multiple addresses at all.  Give each machine
> a single address, whatever network they hook up to they will still be
> reachable.  (ex.  You can reach me, I can reach you but we are not
> only on different subnetworks but across the nation.).

Only because the routing algorithms take advantage of the fact that at
each level of subnetting, all the way from the network number down to
the smallest subnet, each network is fully connected within itself.
Your proposal breaks this.

> Just assign each machine the IP address for their "Home Connection",
> ie if they are in your math subnetwork just assign them an address on
> that subnet.  When they hook up to another net they will operate on
> that net with their own address.

> Admittedly this will only work as long as both subnets can reach each
> other.

It will also be a major nightmare for the routing protocols.  RIP,
which I would guess is the commonest routing protocol within small
(campus-sized) networks, cannot deal with this.  Most UNIX boxes will
be unable to reach the machine when not on its home subnet, unless they
are told that the network isn't subnetted at all and then the gateways
made to do proxy arp - which opens up a whole 'nother can of worms.

No, I don't have any good solution either.  We fortunately have not had
to deal with the problem yet.

					der Mouse

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