--
Uma C.
From: spring [mailto:spring-boun...@ietf.org] On Behalf Of Les
Ginsberg (ginsberg)
Sent: Wednesday, May 04, 2016 9:38 AM
To: Uma Chunduri; bruno.decra...@orange.com; spring@ietf.org
Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
adoption call
Uma –
To restate, the problem being addressed here is to guarantee consistent use of
SIDs in the forwarding plane network-wide in the presence of conflicting
advertisements. The set of advertisements includes both SIDs advertised in
protocol prefix reachability advertisements and SRMS advertisements because
problems occur based upon inconsistencies in what is installed in the
forwarding plane of different routers. It matters not whether Router A used a
SID advertised by a protocol prefix reachability advertisement or by an SRMS
advertisement – what matter is whether the SID used is consistent with what the
neighbors of Router A use. So simply ensuring that OSPF (for example) resolves
SIDs in a consistent way does not fully address the problem space.
More inline.
From: Uma Chunduri [mailto:uma.chund...@ericsson.com]
Sent: Tuesday, May 03, 2016 3:59 PM
To: Les Ginsberg (ginsberg); bruno.decra...@orange.com;
spring@ietf.org
Subject: RE: [spring] draft-ginsberg-spring-conflict-resolution - WG
adoption call
Les,
With all due respects, cross protocol verification of prefix and SID conflicts
as an “architectural change” and it can severely impact the existing
implementations (at least the one I work on).
[Les:] It is quite correct – and I can confirm based on personal experience –
that support for conflict resolution is a significant effort.
Also I have couple of cases where current version of the draft is not clear
about resolution.
IMO, first we need clarity with in a protocol instance resolution rules before
going to resolve the same across protocols (I mentioned few cases below) .
Separation of reachability advertisements and SRMS would help “cross protocol”
verification of the ranges and SRMS is not applicable to all protocols.
In-line [Uma]:
--
Uma C.
From: Les Ginsberg (ginsberg) [mailto:ginsb...@cisco.com]
Sent: Saturday, April 30, 2016 10:11 PM
To: Uma Chunduri; bruno.decra...@orange.com; spring@ietf.org
Subject: RE: [spring] draft-ginsberg-spring-conflict-resolution - WG
adoption call
Uma –
We are indeed defining conflict resolution across all the SID
advertisements regardless of source (protocol or SRMS) –
[Uma]: While you can theoretically do anything for current implementation this
kind of cross protocol verification is a new architectural requirement.
Because it seems “a central entity” need to gather all
different protocol instances SRMS advertisements and should settle with
resolution.
- Also note SRMS is not applicable for BGP but it seems all prefix
SIDs need to be verified with IGP instances SRMS advertisements. Is this true?
While the document mostly talks about these and compares with prefix
advertisement.
[Les:] The issue is protocol agnostic.
- Algorithm proposed needs more clarity: Take Section 3.2.4
o
“ 1. Smaller range wins
2. IPv6 entry wins over IPv4 entry
…
“
What happens in case of prefix conflict or SID conflict with
only prefix advertisements (range 1). Say multiple prefixes have same SID in
one protocol instance and in different protocols.
I see 2 levels of resolution required viz., one at within the
protocol and one among the protocols. No discussion on this.
[Les:] The full set of rules specified in the draft provide deterministic
resolution in all cases. You have snipped only the first two rules. If a
preference is not obtained based on the first two rules you continue on to rule
#3, then rule #4, etc.
Similarly in case of SID conflict (range 1), it’s not
specified which protocol’s SID need to be considered. Are you assuming some
sort of Admin distance play a role in resolution?
[Les:] No – admin distance plays no role here.
I don’t see any discussion in the document and needs more clarity there too.
o Also what happens if a prefix or SID conflict happens with SRMS range 1 and
a prefix advertisement (2 cases)
a. of one protocol and
b. multiple protocols?
[Les:] The source of the SID advertisement (what protocol/protocol instance or
whether it is SRMS based) plays no role. The tie breaker rules as defined are
complete and provide a deterministic answer in all cases.
If you believe that is not true please provide a specific example where you
apply all the rules in the order specified and still do not determine the
preferred entry.
- On the below assumption: (Section 3.2.4)
“This has the nice property that a
single misconfiguratoion of an SRMS
entry with a large range will not be preferred over a large
number of
SIDs advertised in prefix reachability advertisements.”
While anything can happen in theory, I found it bit odd to see why SRMS entry
is being advertised and for the same prefix, SID is also advertised through
reachability advertisements?
This is against the spirit of SRMS advertisement, isn’t it? While this can
happen, it seems we are claiming resolution solution by focusing more on this
case in the current version of the document.
[Les:] There are two legitimate use cases for SRMS:
1)To advertise SIDs for non-SR capable nodes 2)As a global
provisioning tool
Let’s examine the first case. I have an LDP enabled network and I begin
introducing SR capable nodes. At a given moment in time Router A is NOT SR
capable and SRMS advertisements cover prefix SIDs for the addresses associated
with Router A.
I then upgrade Router A to become SR capable. Because I want to do
“make-before-break” I do not immediately remove the SRMS advertisements
covering the addresses associated with Router A. I upgrade A, add configuration
of SIDs locally on Router A, and verify that the advertisements originating
from protocols on Router A are correct. If an inconsistency is introduced when
configuring the SIDs on Router A then I will have an SRMS advertisement and a
prefix-reachability advertisement that conflict. Until the conflict is
corrected we use the conflict resolution rules to provide deterministic
forwarding behavior.
This to me is a normal and expected upgrade scenario.
This is one of the reasons of my first comment below. You got to separate the
reachability advertisements and SRMS advertisements; as in principle these are
defined for different purposes. I don’t see we need algorithm to prefer
reachability advertisement over SRMS advertisement (if we don’t compare these 2
categories).
[Les:] I disagree – hopefully my comments have helped you to understand why.
Les
as the sections you have quoted clearly state.
Why? Because we need consistent use of SIDs in the forwarding plane. From
forwarding perspective it matters not whether the SID was advertised by
protocol instance #1 or #2 or by an SRMS.
What matters is that the SID I use to determine what label I install in my
forwarding plane is the same SID that my neighbors will use. Otherwise
forwarding will be broken.
Les
From: spring [mailto:spring-boun...@ietf.org] On Behalf Of Uma
Chunduri
Sent: Wednesday, April 27, 2016 4:31 PM
To: bruno.decra...@orange.com; spring@ietf.org
Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
adoption call
Dear Authors,
Have few comments on the draft:
1.
As I indicated during meeting - I am not sure why we have to club
verification of SIDs advertised through regular protocol reachability
prefixes and the ranges advertised through 'Mapping Server'
(SRMS). I didn't see any compelling reason to do this.
SIDs advertised through reachability prefixes doesn't have
ranges unlike SRMS advertisements.
As SRMS advertisements are primarily for nodes which are not
SR capable and I feel we should not mix this with nodes which are SR capable.
This isolation helps restricting the resolution work primarily for
multiple SRMS entries advertised through one node or multiple nodes.
SRMS advertisements are indeed little bit unique in that you are
advertising "configuration" on behalf of node X from node Y
with ranges (both prefix ranges and SID ranges).
2.
Regarding the scope of conflict resolution:
Section 1
" The problem to be addressed is protocol independent i.e.,
segment
related advertisements may be originated by multiple nodes using
different protocols and yet the conflict resolution MUST be the same
on all nodes regardless of the protocol used to transport the
advertisements."
Section 3.2.8
" o In cases where multiple routing protocols are in use mapping
entries advertised by all routing protocols MUST be included."
This sounds like we are seeking to resolve conflicting entries outside
and across the protocols?
Each IGP has separate mechanism for advertising mapping entry and I this
is not clear with the current version of the draft how we can cross verify
SID/Prefix conflict across the protocol.
Can you clarify this?
--
Uma C.
-----Original Message-----
From: spring [mailto:spring-boun...@ietf.org] On Behalf Of
bruno.decra...@orange.com
Sent: Thursday, April 14, 2016 12:55 AM
To: spring@ietf.org
Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
adoption call
From: bruno.decra...@orange.com > Sent: Thursday, April 14, 2016
9:51 AM
Dear WG,
As we discussed at our meeting last week, working group adoption has
been requested for draft-ginsberg-spring-conflict-resolution.
Please reply to the list with your comments, including although not
limited to whether or not you support adoption.
We will end the call on April 29, 2016.
Thanks,
--John and Bruno
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