Subject: Re: (NAT) Changes for RSIP protocol -04

From: "Steven M. Bellovin" <[email-masked]>
Date: Mon, 22 Nov 1999 14:43:25 -0500

In message <[email-masked]>, "Iye
r, Prakash" writes:
> 
> Except that in small business / consumer networks, multiple IP addresses may
> not be an option (cost could be a factor). We also assume than in such
> (eventually multi-segment, multi-subnet) networks, a few (order of 10s) of
> these IP addressable entities will access the Internet and will be accessed
> from the Internet. So in a sense, there will be a fair amount of traffic to
> the RSIP server, which will most likely be co-located on a consumer gateway
> type device.

I'm still not making myself clear.  RSIP (and NAT) are like virtual 
memory, if you will.  Virtual memory works if and only if the average demand 
is below some limit corresponding to the amount of real memory available.  If 
you exceed that limit, the system thrashes and no work gets done.

Sure, public addresses are limited, or we wouldn't need concepts like RSIP and 
NAT.  But if there's ever too much demand -- which in turn means too many 
messages -- the whole scheme falls apart.  The only way there can be a lot of 
traffic to a reasonably-sized RSIP server is if very many hosts on the inside 
need public addresses.  That in turn implies very short lifetimes, 
starvatation, and all the other bad things that happen when you can't meet 
your average load.

You say a "few (order of 10s)" will need to talk to the Internet at any one 
time.  How long is each "session"?  It's hard to see how it can be less than a 
minute, which in turn implies a request to the RSIP server every few seconds.
That isn't very much traffic...

		--Steve Bellovin

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From: "Bernard Aboba" <[email-masked]>
Date: Mon, 22 Nov 1999 21:32:17 -0800

>That isn't very much traffic...

Even in scenarios involving 100K users, it is hard to come up with scenarios
in which you have more than a few RSIP transactions/second. For LAN users
accessing the Internet, it can be expected that the host will remain
connected for quite a while, perhaps for hours at a time. So the session
time is quite long, even if most users are online at a time. For WAN
users access the internal network, the session times are shorter, but
only a few users tend to be on at a time.

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