Re: Last Call: <draft-ietf-opsec-ipv6-eh-filtering-06.txt> (Recommendations on the Filtering of IPv6 Packets Containing IPv6 Extension Headers) to Informational RFC

["C. M. Heard" <heard@xxxxxxxxx>]

Greetings,

IMHO, this document is NOT READY for publication in its current form.  In

the introduction it says:

The filtering policy typically depends on where in the network such policy is enforced: when the policy is enforced in a transit network, the policy typically follows a "black-list" approach, where only packets with clear negative implications are dropped. On the other hand, when the policy is enforced closer to the destination systems, the policy typically follows a "white-list" approach, where only traffic that is expected to be received is allowed. The advice in this document is aimed only at transit routers that may need to enforce a filtering policy based on the EHs and IPv6 options a packet may contain, following a "black-list" approach, and hence is likely to be much more permissive that a filtering policy to be employed e.g. at the edge of an enterprise network. The advice in this document is meant to improve the current situation of the dropping of packets with IPv6 EHs in the Internet [RFC7872].

while promoting a **default deny** policy with respect to unknown

extension headers, experimental extension headers, and experimental
options.  If every transit router followed that advice, it would be
impossible to transmit packets containing these things across the open
Internet.  It is especially egregious to dispense that advice for
unknown extension headers, since that would severely impede deployment
of any new extension headers OR any new transport protocols in the open
Internet (as the document itself notes, unknown extension headers are
indistinguishable from unknown upper-layer protocol headers).  This part
of the document's advice does nothing to improve the situation reported
in RFC 7872; if anything, it makes the situation worse.  It certainly
will not make the Internet work better.

While I would prefer to advise operators of transit routers just to be
transparent to everything other than the Hop-by-Hop extensions header,

as discussed in the trailing message thread, adapting the more nuanced
advice in Section 4.4.5 regarding the handling of unknown options to
the cases of unknown EHs and experimental EHs and options would be an

acceptable alternative.  Specific text to that effect follows below.

OLD: 

3.5.3.  Specific Security Implications

   For obvious reasons, it is impossible to determine specific security
   implications of unknown IPv6 EHs.  However, from security standpoint,
   a device should discard IPv6 extension headers for which the security
   implications cannot be determined.  We note that this policy is
   allowed by [RFC7045].

3.5.4.  Operational and Interoperability Impact if Blocked

   As noted in [RFC7045], discarding unknown IPv6 EHs may slow down the
   deployment of new IPv6 EHs and transport protocols.  The
   corresponding IANA registry ([IANA-PROTOCOLS]) should be monitored
   such that filtering rules are updated as new IPv6 EHs are
   standardized.

   We note that since IPv6 EHs and upper-layer protocols share the same
   numbering space, discarding unknown IPv6 EHs may result in packets
   encapsulating unknown upper-layer protocols being discarded.

3.5.5.  Advice

   Intermediate systems should discard packets containing unknown IPv6
   EHs.

NEW:

3.5.3.  Specific Security Implications

   For obvious reasons, it is impossible to determine specific security
   implications of unknown IPv6 EHs.

3.5.4.  Operational and Interoperability Impact if Blocked

   As noted in [RFC7045], discarding unknown IPv6 EHs may slow down the
   deployment of new IPv6 EHs and transport protocols.  The
   corresponding IANA registry ([IANA-PROTOCOLS]) should be monitored
   such that filtering rules are updated as new IPv6 EHs are
   standardized.

   We note that since IPv6 EHs and upper-layer protocols share the same
   numbering space, discarding unknown IPv6 EHs may result in packets
   encapsulating unknown upper-layer protocols being discarded.

3.5.5.  Advice

   Enterprise intermediate systems should discard packets that contain
   unknown IPv6 EHs. Other intermediate systems should permit packets

   that contain unknown IPv6 EHs.  We note that this policy is allowed

   by [RFC7045]. 

OLD:

3.4.10.5.  Advice

   Intermediate systems should discard packets containing these EHs.
   Only in specific scenarios in which RFC3692-Style experiments are to
   be performed should these EHs be permitted.

NEW:

3.4.10.5.  Advice

   Enterprise intermediate systems should discard packets that contain
   these EHs except in specific environments in which RFC3692-Style
   are meant to be performed.  Other intermediate systems should permit

   permit packets with these EHs.

OLD:

4.3.18.5.  Advice

   Intermediate systems should discard packets that contain these
   options.  Only in specific environments where RFC3692-style
   experiments are meant to be performed should these options be
   permitted.

NEW:

4.3.18.5.  Advice

   Enterprise intermediate systems should discard packets that contain
   these options except in specific enviromments in which RFC3692-Style
   are meant to be performed.  Other intermediate systems should permit
   permit packets with these options.

NITS: in some places the abbreviations RHT0 and RHT1 are used, while

in other places RTH0 and RTH1 are used.  The usage should be consistent.

IMHO the former abbreviations seem to be more correct.

Thanks and regards,

Mike Heard

---------- Forwarded message ---------
From: C. M. Heard <heard@xxxxxxxxx>
Date: Thu, Oct 5, 2017 at 9:01 PM
Subject: Re: [OPSEC] WGLC for draft-ietf-opsec-ipv6-eh-filtering-03
To: Ron Bonica <rbonica@xxxxxxxxxxx>
Cc: OPSEC <opsec@xxxxxxxx>, Joe Touch <touch@xxxxxxxxxxxxxx>, Bob Hinden <bob.hinden@xxxxxxxxx>, Brian E Carpenter <brian.e.carpenter@xxxxxxxxx>

Hello Ron,

I think that the direction you propose will make this a much better document. Modulo details it would certainly address my concerns.

I do however have come comments to make about router self-protection. RFC 6192 is all about a router filtering traffic addressed to itself, i.e., what it should process in its role as a host. A very restrictive "white list" policy ( as outlined in RC 6192) is quite in order there. If there is no need or use for extension headers for traffic destined to the control plane, a very restrictive policy of dropping all packets addressed to the control place hat have extension headers may indeed be in order.

It's a very different story, I think, for what a router does to protect itself in its role as forwarding device.  There, if it complies with RFC 8200, the Hop-by-Hop Options header is the only one that can hurt it, if it is able to forward at line rate at all. The choice boils down to whether to process all, some, or no packets with Hop-by-Hop options. I think that we need to loudly broadcast that ignoring all HbH Options headers is a legitimate policy for this purpose, but dropping all packets with HbH Options is not. If we can sell this to the world, it may be possible to actually use the HbH options header, and get rid of abominations such as the CONEX Destination Option.

The way you characterize the proposed second section sounds right on the money to me.

I support your proposed way forward. Thank you.

Mike Heard

On Thu, Oct 5, 2017 at 11:04 AM, Ron Bonica <rbonica@xxxxxxxxxxx> wrote:

Mike,

 

I think that you just struck the note that Fernando and I missed. Transit routers filter extension headers for one of the following reasons:

 

-          To protect themselves (as in RFC 6192)

-          To protect downstream devices

 

Therefore, the document should contain two clearly marked sections, one regarding EH filtering policies that protect the transit router and one regarding EH filtering policies that protect downstream devices.

 

The first section can:

 

-          Be very short (2 pages max)

-          Be guided largely by RFC 8200

-          Speak with some degree of authority (while still INFORMATIONAL)

 

The second section should begin with a discussion of the relationship between the transit router and the downstream devices. Let’s assume that the transit router belongs to an ISP, while downstream devices fall into the following three classes:

 

1)      Belong to the ISP

2)      Belong to parties who want to be protected by the ISP (e.g., its customers)

3)      Belong to other parties

 

Therefore, the transit router MAY discard packets that pose a threat to the first two classes of downstream device, but MUST NOT discard packets that are required by the third class of downstream device.

 

From this point, we formulate a policy that *might* satisfy the above mentioned requirement. We mark this policy with the following caveats:

 

-          It is a best guess

-          If the policy is too permissive, downstream devices belonging to the ISP and those who it protects will not receive all of the protection possible

-          If the policy is too restrictive, downstream devices belonging to other parties will experience collateral damage

-          One size doesn’t fit all

 

If we were to rework the document into this shape, would it address your concerns.

 

                                                               Ron

 

 

 

From: OPSEC [mailto:opsec-bounces@xxxxxxxx] On Behalf Of C. M. Heard
Sent: Wednesday, October 4, 2017 11:08 PM
To: OPSEC <opsec@xxxxxxxx>
Subject: Re: [OPSEC] WGLC for draft-ietf-opsec-ipv6-eh-filtering-03

 

On Thu, 5 Oct 2017 11:10:06 +1300, Brian E Carpenter wrote:

> On 05/10/2017 02:12, Joe Touch wrote:

> 

>> On 9/29/2017 1:12 AM, Van De Velde, Gunter (Nokia - BE/Antwerp) wrote:

>>> 

>>> This is to open a two week WGLC

>>> for https://tools.ietf.org/html/draft-ietf-opsec-ipv6-eh-filtering-03.

>>> 

>> 

>> I do not agree with the claims of this document. It "informationally"

>> advises against support for key IPv6 capabilities and undermines the

>> extensibility of IPv6 by making recommendations about discarding

>> currently unassigned codepoints.

> 

> Here's the problem, Joe. It's a fact of life that many firewalls

> discard a lot of stuff that they shouldn't - that's why we wrote

> RFC 7045 - but in the real world, operators blunder around based

> on folklore and vendors' defaults. We can't change any of that, but

> we can try to issue sensible advice that, overall, will limit the

> resulting breakage. IMHO this document, positioned correctly as

> Informational, will do that: on balance, it makes the world a better

> place.

 

I am afraid that I do not agree that the document, in its present form,

will do that. It says:

 

   The filtering policy typically depends on where in the network such

   policy is enforced: when the policy is enforced in a transit network,

   the policy typically follows a "black-list" approach, where only

   packets with clear negative implications are dropped.  On the other

   hand, when the policy is enforced closer to the destination systems,

   the policy typically follows a "white-list" approach, where only

   traffic that is expected to be received is allowed.  The advice in

   this document is aimed only at transit routers that may need to

   enforce a filtering policy based on the EHs and IPv6 options a packet

   may contain, following a "black-list" approach, and hence is likely

   to be much more permissive that a filtering policy to be employed

   e.g. at the edge of an enterprise network.  The advice in this

   document is meant to improve the current situation of the dropping of

   packets with IPv6 EHs in the Internet [RFC7872].

while at the same time promoting a **default deny** policy with

respect to unrecognized options and unrecognized extension headers.

That is antithetical to the mission of a **transit router**, which

is to get packets transparently from point A to point B. It is

especially egregious to dispense this advice for unrecognized

extension headers, since they are indistinguishable from unrecognized

transport protocols. If these things are blocked by **transit routers**

it becomes  impossible to deploy any new options or transport protocols.

But we already know that, don't we?

If we want to give constructive advice that really will make the

world a better place, we should:

1.) Advise operators of **transit routers** to be transparent to

everything other than the Hop-by-Hop extensions header, and provide

detailed advice on what to do (based on the updates in RFC 8200)

about Hop-by-Hop options. The default should be IGNORE unless there

is an option you need to process.

2.) Reserve all the detailed filtering advicee for operators of

firewalls, enterprise routers, and other systems whose mission it

is to protect the end systems behind them (or to prevent misbehavior

by said end systems). A default deny for unrecognized stuff is not

unreasonable for such systems.

3.) Remind implementors of the following requirement from RFC 7045:

   Forwarding nodes MUST be configurable to allow packets containing

   unrecognised extension headers, but the default configuration MAY

   drop such packets.

and add similar advice for options.

Thanks and regards,

Mike Heard