Subject: Re: [midcom] Protocol eval: 2.1.2 RSIP - proposal to change score and text

From: [email-masked]
Date: Wed, 7 Aug 2002 21:03:47 -0500

Melinda,

Ah, now I understand your comment!

The extra overhead that you're talking about is due to the communication
between the host and the middlebox being carried by a tunnel. That's
true whether the tunnel is a traditional, recognized tunnel type such as
IPsec or IP-IP, or "NAT implemented as a tunnel" as I discussed in my
I-D earlier this year. That overhead appears in the application host, as
opposed to the agent host, and is in addition to the MIDCOM control
channel overhead (small, as compared to the tunnel overhead), assuming
the MIDCOM client is in the application host. Obviously, if the MIDCOM
client is in the agent host, then its small overhead is in that host.

But if NAT is supported in the application host by its normal "default
gateway forwarding model", there is no additional overhead due to the
tunnel. The same comments still apply to the MIDCOM control channel: its
small overhead is in whichever host the MIDCOM client is.

The cost of the tunnel overhead is offset by some benefits. In some
cases the benefits can be realized and are greater than the costs, so it
makes sense to use tunnels. In other cases the benefits either can't be
realized or are not sufficiently greater than the costs to justify the
use of tunnels, so ya don'y use tunnels.

You didn't really expect to get something nothing, now did you? :-)

Jim

Melinda Shore <[email-masked]> on 08/07/2002 07:50:42 AM

Sent by:  Melinda Shore <[email-masked]>

To:   James Renkel/MW/US/3Com
cc:   midcom <[email-masked]>
Subject:  Re: [midcom] Protocol eval: 2.1.2 RSIP - proposal to change score
      and text

> From: [email-masked]

> As I see it, the situation here is no diffrerent for RSIP than for any
> of the other protocols.

The difference may be in magnitude rather than in kind, but
it's certainly there.  With a typical client-server
implementation you're selecting based on a file descriptor
(socket) that has application state associated with it.
With RSIP, as I understand your proposal, you've got the
additional overhead of a "virtual" network interface for the
borrowed address, which pushes more state into the OS or
driver as well as the routing tables.

Melinda

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