Subject: LL4 text

From: Bernard Aboba <[email-masked]>
Date: Fri, 11 Apr 2003 07:09:44 -0700 (PDT)

Before coming up with text for this, I think that we need to have
agreement on the characteristics of applications that will cause them to
fail when used with LLv4 addresses.

I do not believe that just because an application uses LLv4 addresses
that it will fail. The problem is not use by itself -- it is use of
linklocal addresses IPv4 addresses in the wrong context.

If an application uses its LLv4 address in communicating with a host
off the link, it will break. However, if it uses that address in
communicating with a host on-link then that should not happen.

In looking at this, I believe the problem is "leakage". Including an LLv4
address in an off-link application exchange is an example of leakage --
and I believe that this MUST NOT be done at any layer.

Similarly, I do not believe that including domain names in an application
is by itself a problem -- unless it involves leakage. Examples of
leakage include using LLv4 addresses in DNS. Including a name in an
application where DNS is not configured among the conversants is not a
problem -- assuming LLMNR is available to resolve the name.

If the above makes sense, then I do not think it is necessarily
appropriate to come up with "lists of applications" that will
automatically fail. Rather we should focus on what applications need to do
in order to be successful. Here is some proposed text:

"Use of linklocal IPv4 addresses in off-link communication is likely to
cause application failures. This can occur within any application that
includes embedded addresses, if an LLv4 addresses is embedded when
communicating with a host that is not on the link. Examples of
applications that include embedded addresses are found in [RFC3027]. This
includes IPsec, Kerberos 4/5, X-Windows/Xterm/Telnet, FTP, RSVP, SMTP,
SIP, Real Audio, H.323, and SNMP.

In order to prevent use of LLv4 addresses in off-link communication, the
following cautionary measures are advised:

a. Routable addresses should be used within applications whenever they are
available.
b. Names that are globally resolvable to routable addresses should be
used within applications whenever they are available. Names that are
resolvable only on the local link (such as through use of protocols such
as LLMNR) MUST NOT be used in off-link communication. This can be
prevented by using LLv4 addresses or names resolvable on the
local link when an LLv4 address is used as the source address in the
packet.
c. LLv4 addresses MUST NOT be configured in the DNS."

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From: "Philip Nye" <[email-masked]>
Date: Sun, 20 Apr 2003 21:25:38 -0000

> From: "Bernard Aboba" <[email-masked]>
...
> SIP, Real Audio, H.323, and SNMP.

I would add any application which passes URLs, where there is any chance
that those URLs will contain an IP address rather than a name - this
includes HTML, SLP, SSDP and a whole lot more applications.

Philip

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From: Bernard Aboba <[email-masked]>
Date: Sun, 20 Apr 2003 14:40:59 -0700 (PDT)

Sure.