Re: [Lsr] New Version Notification for draft-bonica-lsr-ip-flexalgo-00.txt

Tue, 20 Oct 2020 04:05:00 -0700 

Bruno,

please see inline:



On 20/10/2020 11:43, [email protected] wrote:

Peter,


From: Peter Psenak [mailto:[email protected]]

Bruno,

On 19/10/2020 18:52, [email protected] wrote:

Ron, all,

>From a use case standpoint, I have a use case for having both SR-MPLS and

IP flexalgo in the same network.


>From a protocol standpoint, I think that the functionality could be equally

met by advertising SR-MPLS SID as per RFC 8667 but using a label 3 (implicit
null) to instruct the LER/LSR to not use a label in the forwarding plane. (while
still advertising a label in the control plane because we have to).

does not work,


I could provide more explanations, but reading your email, it seems to me that 
you understood the proposal.
So it seems to me that the opinion that you really meant is: it works but it 
would be an nasty hack.

Regarding "nasty hack" it could be interesting to have a normative definition. 
This could prove useful in some other contexts.
BTW, is "max metric" a hack (vs creating a new tlv if you don't want the link in the IGP 
SPF), is "implicit null label" a hack. And for BGP, encoding the label in the NLRI...
max-metric does not solve the problem, as you would need a prefix metric for non 0 algo anyway. 


Coming back to technical comments, note that creating yet another TLV to carry 
IP prefix also brings questions that the draft does not answer or even raise.
- What about the sub-TLVs? Are they shared with the existing registry for 
prefix TLV [1] ? Do we want to exclude some? E.g., Prefix Segment Identifier 
(we would have two algo fields, two ways to signal SIDs...)
yes, these are details that needs to be addressed, but should not be a problem. Look at locator TLV in SRv6, very similar concept here. 


- for IPv6, the content and meaning of  "ISIS MT IPv6 Flexalgo Prefix Reachability TLV" 
is essentially the same than the "SRv6 Locator TLV".
        - Only the naming and the ordering of the fields are different.
        - Why do we need two TLVs to advertise the same thing (essentially a 
Routing Algo)? Duplication means more spec, more code, more features to 
implement, more error and bugs. (and it did not took long: the draft defines 
the MTID field as 8 bits while RFC 5120 defines it a 12 bits.
well, locator is a construct that is specific to SRv6. Sure you can advertise the prefix in a locator TLV without any SRv6 specific Sub-TLVs and achieve the same thing - I have already mentioned that in one of my responses, but that is again ugly. 


        - What is the functional different between FlexAlgo for SRv6 and 
FlexAlgo for IPv6? Both use the IPv6 destination address in the packet and the 
IPv6 FIB in the router.


they are functionally the same.
I believe that having a clean encoding is preferable in a long run. One can not advertise a prefix as SRv6 locator as well as IP flex-algo prefix (that would be an error), so duplication of data is not an issues. And having a dedicated TLV for each is better from both deployment and implementation perspective. 

thanks,
Peter






Thanks,
Bruno


as it does not allow you to associate the prefix with
Flex-algo without advertising the reachability in algo 0. Making the
prefix reachability in default algo conditional based on the presence of
the Prefix SID Sub-TLV with Imnplicit Null would be a nasty hack.

Not to mention that advertising a Prefix SID in pure IP network would be
ugly.

thanks,
Peter




I feel that this would be less change in the protocol (no new tlv), a good fit

for network requiring both MPLS and IP flex algo, and would not require
implementations/network operator to duplicate the "prefix sub-TLV" [1] on
both advertisements (IP based and SR-MPLS based).


That would still requires a protocol extension/STD track RFC as RFC 8667

does not allow for this. That would still require change to implementations as
only the signalling is different while the feature/behavior is the same (i.e. no
magic).


Regards,
--Bruno

[1] aka "Sub-TLVs for TLVs 135, 235, 236, and 237 (Extended IP reachability,

MT IP. Reach, IPv6 IP. Reach, and MT IPv6 IP. Reach TLVs)"




-----Original Message-----
From: Lsr [mailto:[email protected]] On Behalf Of Ron Bonica
Sent: Tuesday, September 29, 2020 3:38 PM
To: [email protected]
Subject: [Lsr] FW: New Version Notification for draft-bonica-lsr-ip-

flexalgo-

00.txt


Please review and comment

                                         Ron



Juniper Business Use Only


-----Original Message-----
From: [email protected] <[email protected]>
Sent: Tuesday, September 29, 2020 9:36 AM
To: Parag Kaneriya <[email protected]>; Shraddha Hegde
<[email protected]>; Ron Bonica <[email protected]>; Rajesh M
<[email protected]>; William Britto A J <[email protected]>
Subject: New Version Notification for draft-bonica-lsr-ip-flexalgo-00.txt

[External Email. Be cautious of content]


A new version of I-D, draft-bonica-lsr-ip-flexalgo-00.txt
has been successfully submitted by Ron Bonica and posted to the IETF
repository.

Name:           draft-bonica-lsr-ip-flexalgo
Revision:       00
Title:          IGP Flexible Algorithms (Flexalgo) In IP Networks
Document date:  2020-09-29
Group:          Individual Submission
Pages:          14
URL:            https://urldefense.com/v3/__https://www.ietf.org/id/draft-

bonica-

lsr-ip-flexalgo-00.txt__;!!NEt6yMaO-gk!X7PVDP-
FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck80Zbjoij$
Status:
https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-

bonica-lsr-

ip-flexalgo/__;!!NEt6yMaO-gk!X7PVDP-
FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck8x7e5ZqI$
Htmlized:


https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/draft-

bonica-lsr-ip-flexalgo__;!!NEt6yMaO-gk!X7PVDP-


FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck82w_6CyU$

Htmlized:

https://urldefense.com/v3/__https://tools.ietf.org/html/draft-

bonica-lsr-ip-flexalgo-00__;!!NEt6yMaO-gk!X7PVDP-
FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck81_QrJ_p$


Abstract:
     An IGP Flexible Algorithm computes a constraint-based path and maps
     that path to an identifier.  As currently defined, Flexalgo can only
     map the paths that it computes to Segment Routing (SR) identifiers.
     Therefore, Flexalgo cannot be deployed in the absence of SR.

     This document extends Flexalgo, so that it can map the paths that it
     computes to IP addresses.  This allows Flexalgo to be deployed in any
     IP network, even in the absence of SR.




Please note that it may take a couple of minutes from the time of

submission

until the htmlized version and diff are available at tools.ietf.org.

The IETF Secretariat


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