Subject: Re: WG Last Call on IPv4/1394

From: Peter Johansson <[email-masked]>
Date: Thu, 25 Mar 1999 10:33:36 EST

In a message dated 99-03-24 02:57:07 EST, [email-masked] writes:

<<If brige-unaware node accepts an ARP response from a brige-aware node on the
remote bus, it will initiate Async Write transactions to the remote bus. It
may cause some problems.>>

A bridge-unaware node CAN'T initiate transaction requests addressed to a
remote bus---it will be quarantined by its adjacent bridge portal because it
has not identified itself to the bridge. This is why I left "...and responses"
out of the restrictions.

Whatever other details remain under discussion in P1394.1, the working group
is united in its conviction that bridge-unaware nodes cannot be permitted to
originate remote transaction requests.

There is some discussion that might result in a small exception to this
rule---if it can be determined that it is truly safe---but even this proposed
exception (wherein a bridge-aware proxy tells the bridge its OK) would not be
applicable to IP/1394 devices.

Regards,

Peter Johansson

Congruent Software, Inc.
98 Colorado Avenue
Berkeley, CA  94707

(510) 527-3926
(510) 527-3856 FAX

[email-masked]

---

From: Joseph Joy <[email-masked]>
Date: Sat, 27 Mar 1999 18:24:12 -0800

Note that information about the sender ip_address -> hw_address mapping in
BOTH
requests and responses are typically used to populate an ARP s/w modules
ARP cache. Thus one needs to consider both requests and responses when
considering reachability across a bridge.

If we can assume (as Peter indicates) that a bridge-unaware node CAN'T
initiate a
transaction request addressed to a remote bus (in a way applicable to
IP/1394),
can we perhaps remove the paragraph  with the restriction about ignoring
ARP requests/responses ("The recipient of an ARP request SHALL ignore ...")?
The attempt by the "bridge unaware" device to initiate a transaction request
to the remote bus would fail and that failure could be treated as a send
failure. Note that this would not be a common occurrence -- it would almost
certainly be due to a network configuration problem.

But perhaps it is simply unacceptable to allow the possibility for
"bridge unaware" nodes to attempt to initiate a transaction request
addressed
to a remote bus, and this would be the primary reason for retaining the
paragraph
with the restriction.

If the paragraph with the restriction (with "..and responses" included) IS
retained
as is, what is the expected course of events that would lead to successful
IP/1394
implementations that work across bridges -- should we expect an addendum to
the
RFC stating in effect "If the recipient is bridge aware (defined as AAA),
then
the recipient need not ignore the request/response"? (AAA would be defined
at
the time this addendum is made.) That would be a pretty tiny addendum, and
seems
like it would be better avoided.

Instead, how about this modification of the restriction (basically this is a
rewording of what Kenji suggested, with a more specific definition of
"bridge aware"):

        If the recipient of an ARP request or response can not guarantee its
ability to
        initiate transaction requests addressed to a remote bus,
        the recipient SHALL ignore the request or response unless the most
        significant ten bits of the source_ID field in the GASP header are
equal
        to either 0x3FF or the most significant ten bits of the recipient's
        NODE_IDS register. (Probably needs to be rephrased for clarity).

If the above modified restriction is used, current implementations of this
RFC
over current implementations of hw and bus s/w can not meet the above
guarantee and
so WILL ignore ARP requests and responses from another bus. However, when it
DOES
become clear how to meet the guarantee, implementations that can do so can
get
IP connectivity across bridges WITHOUT requiring an addendum to the IP/1394
RFC.

Regards,

Joseph.

-----Original Message-----
From: Peter Johansson [mailto:[email-masked]]
Sent: Thursday, March 25, 1999 7:34 AM
To: [email-masked]
Subject: Re: WG Last Call on IPv4/1394

<<If brige-unaware node accepts an ARP response from a brige-aware node on
the
remote bus, it will initiate Async Write transactions to the remote bus. It
may cause some problems.>>

A bridge-unaware node CAN'T initiate transaction requests addressed to a
remote bus---it will be quarantined by its adjacent bridge portal because it
has not identified itself to the bridge. This is why I left "...and
responses"
out of the restrictions.

There is some discussion that might result in a small exception to this
rule---if it can be determined that it is truly safe---but even this
proposed
exception (wherein a bridge-aware proxy tells the bridge its OK) would not
be
applicable to IP/1394 devices.

Regards,

Peter Johansson

Congruent Software, Inc.
98 Colorado Avenue
Berkeley, CA  94707

(510) 527-3926
(510) 527-3856 FAX

[email-masked]

---

From: "Hattig, Myron" <[email-masked]>
Date: Mon, 29 Mar 1999 11:04:13 -0800

Joseph,

> ARP requests/responses ("The recipient of an ARP request
....
> to a remote bus, and this would be the primary reason for

Any change to the draft should be to add "and responses". It is probably
valid to rely on bridges for proper interoperability, but it is better
to rely on explicit text in the IP/1394 Spec.

> rewording of what Kenji suggested, with a more specific definition of

Defining "bridge aware" is the job of the p1394.1 WG. Their past and
future discussions will allow them to do a much better job of defining
"bridge aware" than the IP/1394 WG. The IP/1394 WG will likely provide
input to the p1394.1's "bridge aware" definition when we define IP/1394
with bridges.

-myron