Bruno -
As the thread below documents, I stated that I did not understand your
representation and asked for clarification - suggesting that you use the format
defined in the draft.
You stated that you could not do that and we were at a point where no progress
could be made.
To illustrate my confusion, one of your examples is:
For R2, the algo evaluates a conflict between the following advertisments:
R2 - SID2 - R2 (MS, MS)
R2 - SID12 - R12 (prefix SID, MS)
R2 - SID12 - R2 (prefix SID, prefix SID)
Now, what does "R2 - SID2 - R2 (MS, MS)" mean?
Does it mean "On R2, SID2 is assigned to prefix R2 from two different mapping
server entries?" I really have no idea.
And you conclude the example by saying
Best one is R2 - SID12 - R2 (smaller range (prefix SID),smaller range (prefix
SID))
==> SID12 is selected for R2.
But since there is no representation of "range" in your examples I really have
no idea how you came to this conclusion .
??
As regards "per FEC/Prefix", I believe this is what "ignore overlap only" does.
Les
From: bruno.decra...@orange.com [mailto:bruno.decra...@orange.com]
Sent: Wednesday, June 29, 2016 7:22 AM
To: Les Ginsberg (ginsberg)
Cc: spring@ietf.org
Subject: RE: draft-ietf-spring-conflict-resolution - Policy
Les,
Thanks for the updated draft.
IINM, you have not answered my below email/proposal. I had waited for the new
version of the draft but it also does not touch this subject.
So, could you please consider and answer my comment?
In short, in an implementation-independent sentence:
> I'm wondering if we could address the conflict on a per FEC/Prefix basis
> rather than on a per IGP advertisement (range) basis.
> If so, this may avoid the discussion between the Quarantine vs ignore policy.
Thanks
Bruno
From: spring [mailto:spring-boun...@ietf.org] On Behalf Of
bruno.decra...@orange.com<mailto:bruno.decra...@orange.com>
Sent: Wednesday, May 18, 2016 1:57 PM
To: Les Ginsberg (ginsberg); spring@ietf.org<mailto:spring@ietf.org>
Subject: Re: [spring] draft-ietf-spring-conflict-resolution - Policy
Les,
Please see inline [Bruno]
From: Les Ginsberg (ginsberg) [mailto:ginsb...@cisco.com]
Sent: Sunday, May 15, 2016 12:41 AM
To: DECRAENE Bruno IMT/OLN; spring@ietf.org<mailto:spring@ietf.org>
Subject: RE: draft-ietf-spring-conflict-resolution - Policy
Bruno -
I am having difficulty parsing the examples you provide below as they seem to
incorporate advertisement source into the description whereas the draft
deliberately omits source.
[Bruno] My text does not incorporate the source, but the type of source IOW the
type of sub-TLV.
So it does not matter if R2 sends an advertisement or R12 sends advertisement
or both of them do (which could happen when an advertisement is leaked) - what
matters is what unique entries are in the database independent of source.
[Bruno] It may not matter for your algorithm (pending another thread), but it
does for the one I proposed.
It would be good if you could present your examples using the format defined in
the draft i.e.:
[Bruno] My examples are described in plain text. Then the examples giving
intermediate steps of my algo uses the data that are needed i.e. the type of
advertisement (Prefix-SID vs MS).
Then finally, my algo runs on a per FEC/IP Prefix basis, and not on a per IGP
advertisement basis which your format describe.
So I'm sorry but I don't see how to indulge your request.
Pi - Initial prefix
Pe - End prefix
L - Prefix length
Lx - Maximum prefix length (32 for IPv4, 128 for IPv6)
Si - Initial SID value
Se - End SID value
R - Range value
T - Topology
A - Algorithm
A Mapping Entry is then the tuple: (Pi/L, Si, R, T, A)
Pe = (Pi + ((R-1) << (Lx-L))
Se = Si + (R-1)
Example: (192.0.2.120/32, 200, 1, 0, 0)
As regards your proposal
- Find all SIDi advertised for the prefix P1
// identification of Prefix conflicts
- For each SIDi find all the prefix Pij associated with SIDi
// identification of SID conflicts
Get the best as per the preference algorithm.
If best Pij == P1
then use SIDij for P1
else return no SID
this to me specifies an implementation - which isn't necessary.
[Bruno] Well, _you_ are the one talking about implementation, and more
specifically implementation complexity.
Assuming the above algo works, it looks relatively simple to implement, in
which case, I would not buy the argument about implementation complexity which
is the only argument in favor or the "ignore" or "quarantine" policy.
Bottom line, I would welcome your feedback and comments on this proposed
algo/policy.
Thanks,
Regards,
-- Bruno
However, there is one important point which has not been specified in the draft
which reading your post has brought to my attention - that is the order in
which checks are made.
The draft states:
"Prefix conflicts are specific to mapping entries sharing the same topology
and algorithm."
"SID conflicts are independent of address-family, independent of prefix len,
independent of topology, and independent of algorithm."
If we consider an example where a network supports two VPNs, the significance
of ordering in the evaluation of conflicts will be highlighted:
VPN1:
(192.0.2.1/32, 100, 1, 1, 0)
(192.0.2.1/32, 200, 1, 1, 0)
VPN2:
(192.0.2.100/32, 200, 1, 2, 0)
If we evaluate prefix conflicts first, then the following entries are "active":
(192.0.2.1/32, 100, 1, 1, 0) !VPN1
(192.0.2.100/32, 200, 1, 2, 0) !VPN2
If we evaluate SID conflicts first, then the following entries are "active":
(192.0.2.1/32, 100, 1, 1, 0) !VPN1
The latter choice is suboptimal because it prevents use of the VPN2 entry
unnecessarily.
This point needs to be made explicit in the draft.
Les
From: spring [mailto:spring-boun...@ietf.org] On Behalf Of
bruno.decra...@orange.com<mailto:bruno.decra...@orange.com>
Sent: Thursday, May 12, 2016 8:23 AM
To: spring@ietf.org<mailto:spring@ietf.org>
Subject: [spring] draft-ietf-spring-conflict-resolution - Policy
Hi authors, all
As an individual contributor, please find below some feedback on the policy.
I'm wondering if we could address the conflict on a per FEC/Prefix basis rather
than on a per IGP advertisement basis.
If so, this may avoid the discussion between the Quarantine vs ignore policy.
The problem that we need to solve, is to find the SID for a prefix (P1).
The algo could be:
- Find all SIDi advertised for the prefix P1
// identification of Prefix conflicts
- For each SIDi find all the prefix Pij associated with SIDi
// identification of SID conflicts
// as a result, we get a list of SIDi - Pij for P1
Get the best as per the preference algorithm.
If best Pij == P1
then use SIDij for P1
else return no SID / no SID available
for this prefix P1
Note that it would probably be better for the preference algo to put the SID
tie-brake before the prefix tie-break as with the prefix tie-break, we suffer
from the conflict twice (Prefix - SID mapping, then SID- prefix mapping) which
increase the diversity and hence the chance of not finding a valid entry. But
for the below examples, I used the preference algo from draft-ietf-*-00
Below are examples, running this policy on typical configuration error cases.
Examples
3.4.4. Network operation
Consider the following simple network example:
1. 100 nodes: R1 to R100;
2. IP Loopbacks are from 192.0.2.1 to 192.0.2.100:
3. SID are from 1 to 100;
4. R1 to R50 are SR capable and advertised their own SID using
Prefix-SID sub-TLV;
5. R51 to R100 are SR non-capable, running LDP and their SID are
advertised by two redundant Mapping Server MS1 and MS2;
6. As the number of nodes which are SR capable are expected to
increase and as in real deployment their Loopback addresses would
no the contiguous, the Mapping servers advertisement covers all
Loopbacks: (192.0.2.1/32, 1, 100);
Subsequent sections evaluate the consequences of a single
configuration error, for all conflict resolution options.
3.4.4.1. Example 1: SID configured on 1 node conflict with SID
configured on another node
Following a typo during configuration, R2 is configured with a SID of
12. That SID conflicts with the Prefix-SID advertised by R12 and the
Mapping Server Advertisement for R12.
Note: both MS advertisement are the same, so we only consider one in the
below analysis.
All prefix but R2 and R12, a single SID is advertised and hence selected.
For R2, the algo evaluates a conflict between the following advertisments:
R2 - SID2 - R2 (MS, MS)
R2 - SID12 - R12 (prefix SID, MS)
R2 - SID12 - R2 (prefix SID, prefix SID)
Best one is R2 - SID12 - R2 (smaller range (prefix SID),smaller range
(prefix SID))
==> SID12 is selected for R2.
For R12, the algo evaluates a conflict between the following advertisments:
R12 - SID12 - R12 (prefix SID, prefix SID)
R12 - SID12 - R2 (prefix SID, prefix SID)
R12 - SID12 - R12 (prefix SID, MS)
R12 - SID12 - R2 (MS, prefix SID)
R12 - SID12 - R12 (MS, MS)
Best one is R12 - SID12 - R2 (smaller range (prefix SID),smaller range
(prefix SID), smaller starting adresse (R2))
R12 <> R2 ==> R12 has no SID.
3.4.4.2. Example 2: SID configured on 1 node conflict with SID
configured on the Mapping Server
Following a typo during configuration, R2 is configured with a SID of
52. That SID conflicts with the Mapping Server advertisements of MS1
and MS2 for the loopback of R52.
Note: both MS advertisement are the same, so we only consider one in the
below analysis.
All prefix but R2 and R52, a single SID is advertised and hence selected.
For R2, the algo evaluates a conflict between the following advertisments:
R2 - SID52 - R2 (prefix SID, prefix SID)
R2 - SID52 - R52 (prefix SID, MS)
R2 - SID2 - R2 (MS, MS)
Best one is R2 - SID52 - R2 (smaller range (prefix SID),smaller range
(prefix SID))
==> SID52 is selected for R2.
For R52, the algo evaluates a conflict between the following advertisments:
R52 - SID52 - R52 (MS, MS)
R52 - SID52 - R2 (MS, prefix SID)
Best one is R52 - SID52 - R2 (smaller range (prefix SID))
R52 <> R2 ==> R52 has no SID.
3.4.4.3. Example 3: wrong configuration of a MS
Following a typo during configuration, MS1 is configured
(192.0.2.0/32, 1, 100). (i.e. 192.0.2.0 instead of 192.0.2.1). That
advertisement conflicts with the Mapping Server advertisements of MS2
and the Prefix-SID advertised by R1...R50.
We have a conflict for all routers except R100.
For LDP only routers R51 to R99 we have a conflict between both MS
advertisement.
For R52, the algo evaluates a conflict between the following advertisments:
R52 - SID52 - R52 (MS2, MS2)
R52 - SID52 - R51 (MS2, MS1)
R52 - SID53 - R52 (MS1, MS1)
R52 - SID53 - R53 (MS1, MS2)
Best one is R52 - SID52 - R51 (smaller starting address)
R52 <> R51 ==> R52 has no SID.
For SR routers, R1 to 50, we have a conflict between both MS advertisement
and Prefix SID advertisements.
For R2, the algo evaluates a conflict between the following advertisments:
R2 - SID 2 - R2 (Prefix SID, Prefix SID)
R2 - SID 2 - R2 (Prefix SID, MS2)
R2 - SID 2 - R1 (Prefix SID, MS1)
R2 - SID 2 - R2 (MS2, MS2)
R2 - SID 2 - R2 (MS2, Prefix SID)
R2 - SID 2 - R1 (MS2, MS1)
R2 - SID 3 - R2 (MS1, MS1)
R2 - SID 3 - R3 (MS1, MS2)
R2 - SID 3 - R3 (MS1, Prefix SID)
Best one is R2 - SID 2 - R2 (Prefix SID, Prefix SID)
R2 == R2 hence R2 use SID2.
Regards,
Bruno
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