Re: rfc4941bis: trying to keep focus

Gyan Mishra <> Sat, 01 February 2020 22:20 UTC

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From: Gyan Mishra <>
Date: Sat, 1 Feb 2020 17:20:03 -0500
Message-ID: <>
Subject: Re: rfc4941bis: trying to keep focus
To: Lorenzo Colitti <>
Cc: "" <>, Fernando Gont <>
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I agree as well with Lorenzo that we should be able to come to consensus on
moving forward with RFC 4941bis.

I understand that in the post Snowden era that privacy and pervasive
monitoring is an IETF objective per RFC 7258 that we have to be cognizant
of across the board.

>From a personal privacy perspective use case connected to the internet on
your home broadband connection or anywhere, you want to limit or eliminate
 ease of pervasive monitoring ; given that sophisticated pervasive
monitoring or attacks will require an IPv6 TOR capability or a anonymity
provider NAT bridge discussed in some of the threads, of course that is out
of scope for this document but valid concerns.

>From an enterprise IT security perspective, with regard to long lived
connections, we would still have the option to disable the temporary
address even with RFC 4941bis if you want a “stable” random address.  That
option could be used if desired,  if the host endpoints are “owned” by the
corporation and are in fact not mobile and remains permanently in the
office .  If the employee owned or private mobile endpoint is used at the
office and taken home or also shared use for “personal” use as well ; the
recommendation would be to not disable the temporary address.  For all the
use cases described above, from an operations perspective, limiting the
valid lifetime down from 7 days to 2 days - drastically reduces the maximum
number of depreciated addresses from 7 down to 2. That is a huge
operational gain that will help enterprises as far as troubleshooting and
availability and MTTR ( mean time to recovery).

Another point as far as “stable” address from an enterprise operations and
MTTR perspective, even though you could a maximum of 7 temporary addresses
for outgoing connections, 1 stable for incoming connections, link local for
ND/RA communications ; total of 9 addresses per RA slaac address-  For
“client host” only the one (preferred) is used.  There maybe home or
enterprise use cases where you are sharing your local drive for
peer-to-peer communications - moreso with home versus enterprise use case.

As a happy medium for the enterprise versus home user connected directly to
the internet the following:

1. Temporary address enabled by Default

2.  Valid lifetime change form 7 to 2

3.  Allow the ability to disable the temporary address if desired.


On Fri, Jan 31, 2020 at 3:44 AM Lorenzo Colitti <lorenzo=> wrote:

> Fernando,
> I agree with all your points. I don't think it's a good idea to pause or
> derail this update because of more general concerns that some participants
> have with temporary addresses in general or with SLAAC in general.
> Temporary addresses have been extremely widely deployed for many years, and
> it seems unlikely that we would degrade them to historic, or that
> implementers would stop implementing them. If there are bugs in RFC 4941
> that impact user privacy, and we can fix them, then we should absolutely do
> so, and do so sooner rather than later.
> Cheers,
> Lorenzo
> On Fri, Jan 31, 2020 at 5:51 AM Fernando Gont <>
> wrote:
>> Folks,
>> I'm trying to summarize what I've seen as part of the recent discussion
>> about (or at least triggered by) rfc4941bis.
>> First, let me give the (obvious) context:
>> rfc4941bis is meant, for the most part, to address flaws in RFC4941 --
>> RFC4941 is a Standards Track document, already. rfc4941bis is not
>> proposing or introducing temporary addresses, but simply addressing
>> flows in the scheme *we already have* (which is widely deployed).
>> Now, let's move to the main topics of this discussion:
>> 1) "temporary addresses results in too many addresses"
>> This is not a problem araising from RFC4941, but a problem with SLAAC.
>> In SLAAC, routers offer network configuration information, and hosts
>> do... what they virtually please.
>> Routers could also advertise many different prefixes on the same link,
>> leading to many addresses. Hosts could also manually configure lots of
>> addresses.  An OS might also provide a proprietary interface for
>> proprietary apps to request "one address per flow".
>> Given a sufficient number of prefixes and hosts, this may get to a point
>> where implementation limits such as the maximum number of NCE may be hit.
>> If folks are concerned about the maximum number of addresses that may be
>> employed in a network (a valid concern), then I guess energy should be
>> spent on how to address this general issue of SLAAC, *in SLAAC*, as
>> opposed to simply bother about one of the many possible ways in which a
>> host may configure addresses.
>> I'd note that we have a BCP (RFC7934) about the topic of "number of
>> addresses". In the typical/default case, RFC4941 will lead to a maximum
>> of 7 addresses per host. In the context of RFC7934, I guess being able
>> to handle 7 addresses per host is the least one could expect. I do
>> understand that some systems can't handle them (given a sufficient
>> number of hosts). Maybe we need to send a signal to router vendors.
>> Maybe a few thousand entries in the NC is way too IPv4ish? All these
>> issues are worth discussing... but they are issues with SLAAC or ipv6
>> network configuration, and not with RFC4941.
>> That said, and given recent feedback, it seems sensible to reduce the
>> preferred lifetime and valid lifetime of temporary addresses to 1 day
>> and 2 days, respectively. This would result in one preferred and one
>> deprecated temporary addresses (as opposed to 1 preferred and 6
>> deprecated addresses resulting from RFC4941).
>> 2) The value of temporary addresses
>> As noted above, one would assume that since RFC4941 has not been
>> deprecated, there is consensus that RFC4941 provides value in the area
>> of privacy.
>> Everytime you reuse an identifier, it leaks information. Temporary
>> addresses reduce the address lifetime, and hence limit the amount of
>> time you reuse an identifier. That's an improvement. And it is a
>> middleground between not using temporary addresses (and hence resuse the
>> same identifier forever) or doing "one address per flow" which, while
>> interesting, would take the number of addresses employed in any network
>> to another dimension. As such (a middle-ground), it can't be expected to
>> be perfect.
>> Temporary addresses are meant employed for outgoing connections. Maybe
>> RFC4941 should provide stronger hints or even recommendations that this
>> use mode is enforced. For connection-oriented transport protocols, the
>> concept is straightforward. For stateless protocols, not so much.
>> But even if this mode is enforced for connection-oriented transport
>> protocols, this would make temporary addresses reduce host exposure
>> quite a lot. This is another area where temporary addresses have value.
>> That said, I'm not sure to what extent it makes sense to argue about the
>> value of temporary addresses in the context of *this* document. If we
>> take the to extreme possible outcomes:
>> * we don't publish rfc4941bis, and we keep a flawed RFC4941
>> * we publish rfc4941bis, and have an improved version of rfc4941
>> Only one of these options will improve RFC4941, and none of them will
>> obsolete rfc4941.
>> 3) Should temporary addresses be enabled by default?
>> One would assume that since RFC4941 has not been deprecated, there is
>> consensus that RFC4941 provides value in the area of privacy.
>> In that sense, and in the context of RFC7258, I believe it would be a
>> hard case to make to have temporary addresses disabled by default.
>> I do believe some network might want to disable them. That would require
>> the network to be able to convey this policy to hosts. This was tried
>> (draft-gont-6man-managing-slaac-policy) and rejected ten years ago.
>> I believe that, at least in the absence of policy, and in the context of
>> RFC7258, it is sensible for the default to be "on".
>> Besides, in a post-Snowden era, I believe we'd nevertheless have a hard
>> time recommending OS vendors to disable them by default.
>> Thanks!
>> Cheers,
>> --
>> Fernando Gont
>> SI6 Networks
>> e-mail:
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Gyan  Mishra

Network Engineering & Technology


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