Re: [bess] Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with DISCUSS and COMMENT)

[Andrew - IETF]

+1

This is something I was a little confused about since its been referenced in 
these emails time and again, and I was wondering if I had missed something, 
but, I’ve checked to be 100%  certain, RFC8950 which is what this document 
refers to explicitly states that the NLRI encoding  of the destination must not 
change – and since the IPv4 NLRI leaves no provision for labels – and  makes it 
clear that SAFI 4 is used for MPLS – MPLS doesn’t fall into SAFI 1.
In fact, what is described in 5.3 only results from the nature of SRv6, it 
states:

   SRv6 Service SID is encoded as part of the SRv6 L3 Service TLV.  The
   SRv6 Endpoint behavior of the SRv6 SID is entirely up to the

   originator of the advertisement.  In practice, the SRv6 Endpoint

   behavior is End.DX4 or End.DT4.

Since 5.3 can operate in SAFI 1 (it explicitly refers to Global IPv4 over SRv6 
core – which by correlation to 8950 is SAFI 1) and based on the wording of the 
above, this actually puts MPLS type functionality into SAFI 1 where it never 
was before, by using the SID as a normal address which is then dealt with as a 
SID inside the domain.  But no – this is not providing equal functionality for 
MPLS – this is extending MPLS style functionality into SAFI 1, which, if my 
reading of Warren’s discuss is accurate, is pretty much the essence of the 
problem.

Thanks

Andrew

From: Robert Raszuk 
Sent: Sunday, February 13, 2022 3:48 PM
To: Gyan Mishra 
Cc: Andrew - IETF ; BESS ; Bocci, 
Matthew (Nokia - GB) ; The IESG ; 
Warren Kumari ; bess-cha...@ietf.org; 
draft-ietf-bess-srv6-servi...@ietf.org
Subject: Re: [bess] Warren Kumari's Discuss on 
draft-ietf-bess-srv6-services-10: (with DISCUSS and COMMENT)

Gyan,

MPLS is never sent in SAFI 1.

Thx,
R.

On Sun, Feb 13, 2022 at 5:47 AM Gyan Mishra 
mailto:hayabusa...@gmail.com>> wrote:
Hi Robert

On Sat, Feb 12, 2022 at 4:23 PM Robert Raszuk 
mailto:rob...@raszuk.net>> wrote:
Gyan,

Section 5.3 and 5.4 cover GRT option and 5.3 using RFC 5549 next hop encoding.  
In this case using GRT transport underlay layer now carry’s the customer routes 
and that is what Warren and Andrew concern is as far as BGP leaks.

I would have the same concern so would VPN customers. No one is selling L2 or 
L3 VPN service to them distributing their reachability in the global routing 
table. They can do that all by themselves and there is lot's of really solid 
tools or products to do that already without being locked to a single telco.

Gyan> MPLS provides the capability for GRT native routing  SAFI 1 as well as 
SAFI 128, so in my opinion both should be supported by SRV6 as operators look 
to use SRv6 for a variety of use cases. That’s my point as there should be 
complete feature parity between MPLS and SRv6 as to AFI / SAFI support.  Global 
Internet routing would not be the best use case for SAFI 1 GRT due to the 
attack vector - agreed, but enterprise networks with internal customers where 
there is a trust level is a huge use case.

So when GRT is used the same edge filtering protection mechanisms used today 
for MPLS and SR-MPLS would apply to SRv6 for GRT use case.

Not possible. It is not about filtering ... it is all about using globally 
routable SAFI vs private SAFIs to distribute customer's reachability, IMO that 
should still be OTT only.

Gyan> As SRv6 source node is requirement to encapsulation with IPv6 outer 
header and decapsulation at egress PE for SRv6-BE and SRv6-TE path steering the 
security issue brought up related to 5.3 and 5.4 is not an issue requiring 
filtering per RFC 8402.  So routable and private SAFI scenario would be the 
same now due to encapsulation overlay for both.  Do you agree ?

I don’t think we are saying 5.3 or 5.4 should not be allowed but just to 
tighten up verbiage as far securing the domain.

BGP filtering or policy is in hands of many people. As has been proven you can 
not tighten them strong enough not to leak. The only natural way to tighten 
them is to use different plane to distribute private information what in this 
context means at least different BGP SAFI.

So no - I do not agree with your observations.

   Gyan> I am not promoting use of SAFI 1 however I SRv6 should provide 
complete parity with MPLS to support both SAFI 1 and 128. There  are plenty of 
use cases for SAFI 1 and it should be supported with SRv6.

However I am for providing overlay reachability over global IPv6 Internet to 
interconnect customer sites. But routing within those sites should not be 
traversing Internet routers and using SAFI 1.

Rgs,
Robert.

--

[Image removed by sender.]<http://www.verizon.com>

Gyan Mishra

Network Solutions Architect

Email gyan.s.mis...@verizon.com<mailto:gyan.s.mis...@verizon.com>

M 301 502-1347

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Re: [bess] Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with DISCUSS and COMMENT)

[Andrew - IETF]

Hi Gyan,

A few clarifications on your clarifications – see responses inline:
RFC8402 Section 8.2 explicitly prohibits sending SRv6 traffic beyond the 
borders of a domain and over the general internet.  Making use of traffic 
destined for an address within the SRGB of another network isn’t permitted as 
per:
 Gyan> The purpose of the domain boundary filters is to protect the SRv6 nodes 
within the “underlay” by filtering external traffic at the boundary edges any 
traffic destined to any IPv6 destination address within the SRGB or SRLB which 
would be underlay node connected interfaces IGP routable not in BGP. This is 
done for any internet or intranet MPLS domain today to secure the domain trust 
boundary.
Andrew> Can I presume when referring to the SRGB/SRLB here you are referring to 
the function part of the address or function+argument portion of the SID’s? I 
point out that the difference between SRv6 and MPLS/SR-MPLS is that you cannot 
“Route” towards a label – you can route towards an IPv6 address.
If my assumptions are correct on the above – there seems to be an assumption 
here that there is differentiation between the locator and the 
function+argument parts of the SID – and these things are advertised separately 
and then some how assembled.  Except – I know of no draft text that says that, 
nor have I ever seen that behavior in the wild.  If my assumptions are accurate 
and that is what you are saying, can you point me to the text that defines this 
reassembly.
As regards the BGP – it goes further still:


 Gyan> This is not a BGP related just IGP underlay related.  BGP prefix sid 
attribute is used to encode SRv6 L3 service TLVs within the SR domain basically 
mapping the VPN and GRT BGP AFI/SAFI into the Function field of SRv6 SID 
equivalent to MPLS VPN service label bottom of stack.  However this is only 
within the SRv6 domain and once the packet leaves the SRv6 domain it’s native 
BGP AFI/SAFI encoding and not in SRv6 SID.  So even though SRv6 SID contains 
the BGP service label encoding it is not BGP overlay encoding that needs to be 
secured providing transitivity.
Andrew> Again, I’m pretty unsure that I’m fully understanding what you are 
saying here.  You seem to be saying that once a SID – including its 
function/locator leave the domain – they cease to be SID’s and are just normal 
addresses – and only become SID’s by dint of the fact that they are inside the 
domain.  This would imply that a destination on the internet – suddenly 
transmutes to something else when it crosses the domain boundary. I would this 
is an unclear argument that seems to assume behavior not stated in this 
document, or other SRv6 documents that I have read – and I’m not sure that I 
agree with this assertion (if I am interpreting you correctly).  I am drawing 
my interpretations here from the fact that you are bringing up the IGP – and 
seem to be implying that a locator is announced and some how combined with IGP 
information, and there is some kinda split / reassembly of the destination.
Gyan> SR provides a means of stateless traffic steering in the underlay 
framework using IGP extension to provide the SID distribution  for both SR-MPLS 
and SRv6.  The SID distribution is done via the IGP extensions as part of the 
underlay.  The underlay is not routable reachable from outside the domain and 
even in MPLS TTL propagation is disabled to hide the visibility.  One big 
difference between MPLS and SRv6 is that the SR source node encapsulates the 
PE-CE AC payload in IPv6 outer header for both VPN overlay and GRT traffic so 
they are both treated the same where MPLS with GRT the customer traffic is 
natively routed and no overlay encapsulation.  However in both cases of course 
we have a BGP overlay RIB which carry the internet or intranet table and that 
is transitory traffic and is not filtered at the trust boundary.
So the trust boundary filtering is primary goal is to protect the underlay 
nodes and not interfere with the transitory BGP routing reachability.

Andrew> However, if all assumptions I have made in the above are correct, and 
we are back to border filtering, that still leaves the question of the fact 
that the SID’s are exposed (albeit as addresses) – which still leads to the 
problem of the fact that this seems to rely on perfect bgp filtering in 
combination with perfect border filtering, and a failure in either that could 
have catastrophic consequences.
Thanks

Andrew

From: Gyan Mishra mailto:hayabusa...@gmail.com>>
Sent: Saturday, February 12, 2022 10:18 PM
To: Robert Raszuk mailto:rob...@raszuk.net>>
Cc: Andrew - IETF mailto:andrew-i...@liquid.tech>>; 
BESS mailto:bess@ietf.org>>; Bocci, Matthew (Nokia - GB) 
mailto:matthew.bo...@nokia.com>>; The IESG 
mailto:i...@ietf.org>>; Warren Kumari 
mailto:war...@kumari.net>>; 
bess-cha...@ietf.org<mailto:bess-cha...@ietf.org>; 
draft-ietf-bess-srv6-servi...@ietf.org<mail

Re: [bess] Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with DISCUSS and COMMENT)

[Andrew - IETF]

Gyan,

However what you say then raises additional concerns.

RFC8402 Section 8.2 explicitly prohibits sending SRv6 traffic beyond the 
borders of a domain and over the general internet.  Making use of traffic 
destined for an address within the SRGB of another network isn’t permitted as 
per:

   SR domain boundary routers MUST filter any external traffic destined
   to an address within the SRGB of the trusted domain or the SRLB of
   the specific boundary router.  External traffic is any traffic
   received from an interface connected to a node outside the domain of
   trust.

As regards the BGP – it goes further still:

   From a network-protection standpoint, there is an assumed trust model
   such that any node adding an SRH to the packet is assumed to be
   allowed to do so.  Therefore, by default, the explicit routing
   information MUST NOT be leaked through the boundaries of the
   administered domain.

Now, I may be misunderstanding here – but – if at any point the announcements 
lead to traffic flowing towards a SID from outside the administered domain – 
that violates 8402.  If the SID’s are in BGP prefix’s that are transitive and 
find their way onto the general internet – that also violates 8402.

Now, this could be a misunderstanding on my part – so I’d welcome clarification 
if I am incorrect in what I am seeing here – which may also lead to text which 
is clearer (as a note, I ran this past several operators who had very similar 
readings to what I had – so – if it’s a matter of misunderstanding, we really 
do need to find a way to clarify it, if its not a misunderstanding, then we 
need to find a way to rectify it for security purposes and to bring it in-line 
with RFC8402.

Thanks

Andrew


From: Gyan Mishra 
Sent: Saturday, February 12, 2022 10:18 PM
To: Robert Raszuk 
Cc: Andrew - IETF ; BESS ; Bocci, 
Matthew (Nokia - GB) ; The IESG ; 
Warren Kumari ; bess-cha...@ietf.org; 
draft-ietf-bess-srv6-servi...@ietf.org
Subject: Re: [bess] Warren Kumari's Discuss on 
draft-ietf-bess-srv6-services-10: (with DISCUSS and COMMENT)


Hi Robert / All

For service providers and enterprises using GRT or VRF to carry the internet or 
intra internet  routing table using MPLS today or SR-MPLS that would like to 
use SRv6 to provide the same service.

Section.  5.1 and 5.2 cover the VPN case in which the customer traffic is in 
VRF overlay and the SRv6 transport layer is a closed domain.

Section 5.3 and 5.4 cover GRT option and 5.3 using RFC 5549 next hop encoding.  
In this case using GRT transport underlay layer now carry’s the customer routes 
and that is what Warren and Andrew concern is as far as BGP leaks.

So when GRT is used the same edge filtering protection mechanisms used today 
for MPLS and SR-MPLS would apply to SRv6 for GRT use case.

I don’t think we are saying 5.3 or 5.4 should not be allowed but just to 
tighten up verbiage as far securing the domain.

As far as the SRv6 domain is concerned even with GRT the domain is still closed 
at the PE ingress and egress points which is where the concern is for BGP 
leaks.  The BGP Prefix SID encoding the SRv6 L3 service TLVs would, the 
encoding would only be present in the SRv6 SID Function field within the closed 
domain, and once you exit the SRv6 domain at the ingress or egress endpoints 
the SRv6 L3 service TLVs would now be carried natively in BGP and not in the 
SRv6 BGP prefix SID encoding.


   When an egress PE is enabled for BGP Services over SRv6 data-plane,

   it signals one or more SRv6 Service SIDs enclosed in SRv6 Service

   TLV(s) within the BGP Prefix-SID Attribute attached to MP-BGP NLRIs

   defined in [RFC4760<https://datatracker.ietf.org/doc/html/rfc4760>] 
[RFC4659<https://datatracker.ietf.org/doc/html/rfc4659>] 
[RFC8950<https://datatracker.ietf.org/doc/html/rfc8950>] 
[RFC7432<https://datatracker.ietf.org/doc/html/rfc7432>] 
[RFC4364<https://datatracker.ietf.org/doc/html/rfc4364>]

   [RFC9136<https://datatracker.ietf.org/doc/html/rfc9136>] where applicable as 
described in Section 
5<https://datatracker.ietf.org/doc/html/draft-ietf-bess-srv6-services#section-5>
 and Section 
6<https://datatracker.ietf.org/doc/html/draft-ietf-bess-srv6-services#section-6>.

So as far as SRv6 SID leaking there would not be any leaking outside the SRv6 
domain.

However as the GRT carry internet or intranet BGP RIB the SP AS is of course 
transitive so entire table is propagated.  That’s not a leak.

I think we just need to maybe tighten up the verbiage on securing the PE edges 
of the SRv6 domain.

Kind Regards

Gyan


On Sat, Feb 12, 2022 at 1:37 PM Robert Raszuk 
mailto:rob...@raszuk.net>> wrote:
Hi Andrew,

When I read Warren's note Iooked at this text from section 2 which says:

- - -

   The SRv6 Service TLVs are defined as two new TLVs of the BGP Prefix-
   SID Attribute to achieve signaling of SRv6 SIDs for L3 and L2
   services.

   o  SRv6 L3 Service TLV: This TLV e

Re: [bess] Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with DISCUSS and COMMENT)

[Andrew - IETF]

Hi Robert,

5.3 Also opens the door to SAFI 1 – since you can v6 over v4 using AFI  1  / 
SAFI 1 using what is defined in RFC8950, in fact, it is explicit.

Section 5.3 is titled Global IPv4 over SRv6 core – this correlates with the 
example in section 6.1 of RFC8950 – which states:



   The extensions defined in this document may be used as discussed in

   [RFC5565<https://datatracker.ietf.org/doc/html/rfc5565>] for the 
interconnection of IPv4 islands over an IPv6

   backbone.  In this application, Address Family Border Routers (AFBRs;

   as defined in [RFC4925<https://datatracker.ietf.org/doc/html/rfc4925>]) 
advertise IPv4 NLRI in the MP_REACH_NLRI

   along with an IPv6 next hop.



   The MP_REACH_NLRI is encoded with:



   *  AFI = 1



   *  SAFI = 1



   *  Length of Next Hop Address field = 16 (or 32)



   *  Next Hop Address = IPv6 address of the next hop



   *  NLRI = IPv4 routes



   During BGP Capability Advertisement, the PE routers would include the

   following fields in the Capabilities Optional Parameter:



   *  Capability Code set to "Extended Next Hop Encoding"



   *  Capability Value containing 

As I say, if you were to remove the references to global and 5.3/5.4 which 
explicitly reference it and bring SAFI 1 into play – there would be far less 
concern from my side, I can’t speak for anyone else, but that would be my 
feeling

Thanks

Andrew



From: Robert Raszuk 
Sent: Saturday, February 12, 2022 9:37 PM
To: Andrew - IETF 
Cc: Warren Kumari ; Bocci, Matthew (Nokia - GB) 
; draft-ietf-bess-srv6-servi...@ietf.org; 
bess-cha...@ietf.org; The IESG ; BESS 
Subject: Re: Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with 
DISCUSS and COMMENT)

Hi Andrew,

When I read Warren's note Iooked at this text from section 2 which says:

- - -

   The SRv6 Service TLVs are defined as two new TLVs of the BGP Prefix-
   SID Attribute to achieve signaling of SRv6 SIDs for L3 and L2
   services.

   o  SRv6 L3 Service TLV: This TLV encodes Service SID information for
  SRv6 based L3 services.  It corresponds to the equivalent
  functionality provided by an MPLS Label when received with a Layer
  3 service route as defined in [RFC4364] [RFC4659] [RFC8950]
  [RFC9136].  Some SRv6 Endpoint behaviors which MAY be encoded, but
  not limited to, are End.DX4, End.DT4, End.DX6, End.DT6, etc.

   o  SRv6 L2 Service TLV: This TLV encodes Service SID information for
  SRv6 based L2 services.  It corresponds to the equivalent
  functionality provided by an MPLS Label1 for Ethernet VPN (EVPN)
  Route-Types as defined in [RFC7432].  Some SRv6 Endpoint behaviors
  which MAY be encoded, but not limited to, are End.DX2, End.DX2V,
  End.DT2U, End.DT2M etc.

   When an egress PE is enabled for BGP Services over SRv6 data-plane,
   it signals one or more SRv6 Service SIDs enclosed in SRv6 Service
   TLV(s) within the BGP Prefix-SID Attribute attached to MP-BGP NLRIs
   defined in [RFC4760] [RFC4659] [RFC8950] [RFC7432] [RFC4364]
   [RFC9136] where applicable as described in Section 5 and Section 6.

   The support for BGP Multicast VPN (MVPN) Services [RFC6513] with SRv6
   is outside the scope of this document.

- - -

This limits the overlay signalling to non global SAFIs mainly SAFI 128 and SAFI 
70.

To your note SAFI 4 is private and never exchanged in the wild. Also SAFI 2 is 
multicast which is out of scope of this draft.

The only thing which we need to sync on is indeed section 5.4 and use of global 
IPv6 AFI 2 & SAFI 1

Many thx,
R.




On Sat, Feb 12, 2022 at 7:11 PM Andrew - IETF 
mailto:andrew-i...@liquid.tech>> wrote:
Robert,

I have to say that I have very similar readings on parts of the draft.

Let’s look at it –

5.1 uses the IPv4-VPN NLRI – That would seem to indicate AFI 1 / SAFI 4
5.2 – Uses AFI 2 / SAFI 4 from my reading
5.3 – According to RFC8950 – allows advertisement over SAFI 1, 2 or 4
5.4 – To my reading – very much refers to AFI 2 / SAFI 1.

I would agree if this document limited itself to 5.1 and 5.2 – it doesn’t – and 
therefore I have to agree with the thoughts expressed in Warrens Discuss.  If I 
am wrong about 5.3 and 5.4, let’s chat and help me understand this better, and 
then lets potentially see if we can work up some wording that would clarify 
this if that is what is required.

Thanks

Andrew


From: iesg mailto:iesg-boun...@ietf.org>> On Behalf Of 
Robert Raszuk
Sent: Saturday, February 12, 2022 8:26 PM
To: Warren Kumari mailto:war...@kumari.net>>
Cc: Bocci, Matthew (Nokia - GB) 
mailto:matthew.bo...@nokia.com>>; 
draft-ietf-bess-srv6-servi...@ietf.org<mailto:draft-ietf-bess-srv6-servi...@ietf.org>;
 bess-cha...@ietf.org<mailto:bess-cha...@ietf.org>; The IESG 
mailto:i...@ietf.org>>; BESS 
mailto:bess@ietf.org>>
Subject: Re: Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with 
DISCUSS and COMMENT)

Hi Warren,

Than

Re: [bess] Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with DISCUSS and COMMENT)

[Andrew - IETF]

Robert,

I have to say that I have very similar readings on parts of the draft.

Let’s look at it –

5.1 uses the IPv4-VPN NLRI – That would seem to indicate AFI 1 / SAFI 4
5.2 – Uses AFI 2 / SAFI 4 from my reading
5.3 – According to RFC8950 – allows advertisement over SAFI 1, 2 or 4
5.4 – To my reading – very much refers to AFI 2 / SAFI 1.

I would agree if this document limited itself to 5.1 and 5.2 – it doesn’t – and 
therefore I have to agree with the thoughts expressed in Warrens Discuss.  If I 
am wrong about 5.3 and 5.4, let’s chat and help me understand this better, and 
then lets potentially see if we can work up some wording that would clarify 
this if that is what is required.

Thanks

Andrew


From: iesg  On Behalf Of Robert Raszuk
Sent: Saturday, February 12, 2022 8:26 PM
To: Warren Kumari 
Cc: Bocci, Matthew (Nokia - GB) ; 
draft-ietf-bess-srv6-servi...@ietf.org; bess-cha...@ietf.org; The IESG 
; BESS 
Subject: Re: Warren Kumari's Discuss on draft-ietf-bess-srv6-services-10: (with 
DISCUSS and COMMENT)

Hi Warren,

Thank you for your Discuss. But before we start discussing it perhaps it would 
be good to align on what this document really defines as I am sensing from your 
description there can be some disconnect (modulo some text may be indeed 
misleading in the draft).

You said:

> However, we all know that BGP leaks happen -- and when they do, the SID’s
> contained in the leak will be logged by various systems and hence available to
> the public into perpetuity.

I think the term BGP is used here a bit too broadly.

Leaks do happen but only within global AFI/SAFIs. This draft defines extensions 
for L3VPN and L2VPNs SAFIs which are not used to peer outside of a domain, 
collection of domains under same administration + of course inter-as also could 
happen.

With that being said I do not see risk that due to leaking there could be a 
situation where customer networks are exposed in any way externally - leaving 
alone that to even get at the transport level to the customer facing PE is also 
filtered and never allowed from outside. But this is out of scope of this 
document as here the focus is not on underlay but overlay.

Now when I re-read this I see why there is a little piece perhaps misleading. 
The draft makes a claim that it is applicable to RFC8950 which defines use of 
NHv6 with both unicast and VPN AFs. That needs to be made clear that it is 
applicable to the latter only. If other co-authors believe this is applicable 
to the former your DISCUSS section would indeed be valid.

Many thx,
R.




On Sat, Feb 12, 2022 at 12:05 AM Warren Kumari via Datatracker 
mailto:nore...@ietf.org>> wrote:
Warren Kumari has entered the following ballot position for
draft-ietf-bess-srv6-services-10: Discuss

When responding, please keep the subject line intact and reply to all
email addresses included in the To and CC lines. (Feel free to cut this
introductory paragraph, however.)


Please refer to 
https://www.ietf.org/blog/handling-iesg-ballot-positions/
for more information about how to handle DISCUSS and COMMENT positions.


The document, along with other ballot positions, can be found here:
https://datatracker.ietf.org/doc/draft-ietf-bess-srv6-services/



--
DISCUSS:
--

The Security Considerations section says: "The service flows between PE routers
using SRv6 SIDs advertised via BGP are expected to be limited within the
trusted SR domain (e.g., within a single AS or between multiple ASes within a
single provider network).  Precaution should be taken to ensure that the BGP
service information (including associated SRv6 SID) advertised via BGP sessions
are limited to peers within this trusted SR domain." This is related to (from
RFC8402): "Therefore, by default, the explicit routing information MUST NOT be
leaked through the boundaries of the administered domain."

However, we all know that BGP leaks happen -- and when they do, the SID’s
contained in the leak will be logged by various systems and hence available to
the public into perpetuity.

While the document states that border filtering should protect against traffic
injection, this does not cover the case of internal compromise. Sure, there is
the argument that once there is an internally compromised system, all bets are
off -- but with this, an attacker that knows the SIDs in e.g inject traffic
into a VPN. This seems to me to significantly expand the attack surface to
include the customer's networks too.

Not only does an operator have to ensure that BGP leaks never occur, they have
to then ensure that at no point can there be any filter lapses at any border
node, and be able to guarantee the security of every device, server and machine
within the domain in order for a secure