Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

[Michael McBride <[e-mail]>]

Hi Hooman,

Thanks for the comments. I'd recommend we follow the same path as was done with sr-p2mp-policy, ie, we continue the call for adoption in pim and see if there is support. If no wg support we drop it. If there is support, we (actually Stig since I'm on the draft) will contact the spring chairs before adoption. The spring chairs have been more than happy for pim to take on spring+mcast work. It was our AD, not spring or pim chairs, who requested we hold off and wait for the replication-segment draft before pim adoption. Like you, they may suggest that this srv6-p2mp draft should also have a base SID concept draft done in spring.

Stig should take it from here.

mike

From: pim <[e-mail]> On Behalf Of Bidgoli, Hooman (Nokia - CA/Ottawa)
Sent: Sunday, January 17, 2021 1:17 PM
To: Huaimo Chen <[e-mail]>; Jeffrey (Zhaohui) Zhang <zzhang=[e-mail]>; Stig Venaas <[e-mail]>; [e-mail]; 'Toerless Eckert' <[e-mail]>
Subject: Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

Hi Huaimo

Since you are answering my concerns as well in this email I will add my two cent.

1.            "The PIM WG has agreed with the SPRING WG to work on multicast+spring work which is why draft-ietf-pim-sr-p2mp-policy is adopted."

HB> This is not my understanding, chairs please clarify the confusion here, it is important to have a clear mandate for the WG.

This is why the chairs insisted for the adaptation of draft-ietf-spring-sr-replication-segment first before the pim working group adopted draft-ietf-pim-sr-p2mp-policy. The draft-ietf-pim-sr-p2mp-policy only talks about how a P2MP tree is built via candidate paths and the PCE etc... and it uses the replication segment, which is being worked on in the spring WG, as its building block.

I think it is very important to clarify the SID concept introduced in this draft with spring first.



Thanks

Hooman


From: Huaimo Chen <[e-mail]<mailto:[e-mail]>>
Sent: Friday, January 15, 2021 8:32 PM
To: Jeffrey (Zhaohui) Zhang <zzhang=[e-mail]<mailto:zzhang=[e-mail]>>; Bidgoli, Hooman (Nokia - CA/Ottawa) <[e-mail]<mailto:[e-mail]>>; Stig Venaas <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>; 'Toerless Eckert' <[e-mail]<mailto:[e-mail]>>
Subject: Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

Hi Jeffrey,

    My responses are inline below with prefix [HC].

Best Regards,
Huaimo on behalf of authors

________________________________
From: pim <[e-mail]<mailto:[e-mail]>> on behalf of Jeffrey (Zhaohui) Zhang <zzhang=[e-mail]<mailto:zzhang=[e-mail]>>
Sent: Tuesday, January 12, 2021 1:46 PM
To: Bidgoli, Hooman (Nokia - CA/Ottawa) <[e-mail]<mailto:[e-mail]>>; Stig Venaas <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>; 'Toerless Eckert' <[e-mail]<mailto:[e-mail]>>
Subject: Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

I object to the adoption, for the following reasons:

1. As Hooman pointed out, this should first be discussed in the SPRING WG first, and perhaps homed there.
[HC]: It seems that this should be discussed in the PIM WG first.
The reasons include:
1) The PIM WG has agreed with the SPRING WG to work on multicast+spring
work which is why draft-ietf-pim-sr-p2mp-policy is adopted.
2) This is about multicast.
3) For the document focusing on one topic (called X) and related to
another topic (called Y), it is better to discuss it in the WG for X.
For example, RFC 4203 OSPF Extensions in Support of GMPLS, focusing
on GMPLS and related to OSPF, its home WG is CCAMP, not OSPF.
Similarly, the home WG for this should be PIM, not SPRING.

2. Regardless which WG is the right home, this is not a practical solution - you won't be able to encode much of the tree in the data packet even when you use uSID. If you want to remove the per-tree state in the network and still achieve effective replication, you either do BIER or BIER-TE (https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fdraft-ietf-bier-te-arch%2F&amp;data=04%7C01%7Chuaimo.chen%40futurewei.com%7C41c897da80ec41896e9f08d8b72a5ebc%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637460739895958398%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=ga2B%2Fgo%2B7POZhifAUyNItFh52LBZqzwMH1HUXBRFHrY%3D&amp;reserved=0<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fdraft-ietf-bier-te-arch%2F&data=04%7C01%7Cmichael.mcbride%40futurewei.com%7C39d40656a24546dd773e08d8bb2d45ab%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637465150439791300%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=AioRMsWLJHy3ff2on0C%2FrYnyHFnW96VsK1aU%2FBrC%2Fmo%3D&reserved=0>). BIER-TE would scale better than this.
[HC]: This should be a practical solution.
The reasons include:
1) This provides an alternative solution for multicast using SR.
For people operating a network with SR, they do not need to deploy
BIER-TE. This may reduce their Opex to Capex.
2) The scalabilities of this (called SR-P2MP) and BIER-TE depend on different
factors such as SID compression for SR-P2MP and BitPositions encoding for
BIER-TE. Consider an explicit multicast tree traversing through N links,
there are N SIDs in SR-P2MP, and N BitPositions in BIER-TE.
Assume that the size of compressed SID is u bits, the overhead of SR-P2MP
is N*u bits.
Suppose that the size of SI and BitString are s and b bits respectively, and
the maximum number of possible BitPositions is M bits, the overhead of BIER-TE
is M bits if a maximum BitString is used,
(in this case, M may greater than N*u. For example, when M = 10k, u = 40,
M > N*u for N < 10k/40)
up to N*(s+b) if bit sets are used.
(in this case, N*(s+b) may greater than N*u. For example, when b = 64, s = 10,
u = 40, N*(s+b) > N*u )

3. If this did not involve new forwarding scheme (i.e. new hardware) one could argue that multiple solutions could be developed. But given that this does need new hardware and does not do better than alternatives (e.g. BIER-TE), why bother.
[HC]: It seems that both SR-P2MP and BIER-TE are involved with new forwarding schemes.

BTW, the encoding scheme in this solution is similar to https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-zhang-qos-ospf-01%23section-6.1.3&amp;data=04%7C01%7Chuaimo.chen%40futurewei.com%7C41c897da80ec41896e9f08d8b72a5ebc%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637460739895968353%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=9zwA%2B%2FblwWrvpWEmh5K%2Fu9nrdExX4jX%2BqavjP9T1sKk%3D&amp;reserved=0<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-zhang-qos-ospf-01%23section-6.1.3&data=04%7C01%7Cmichael.mcbride%40futurewei.com%7C39d40656a24546dd773e08d8bb2d45ab%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637465150439801296%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=YPQiLAmuED%2B27xK%2B0Ea9ECxh21yTToMkDrafBJEPR9s%3D&reserved=0>. Of course, that one is for control plane only.
[HC]: The functions of the two encodings are the same, which are
to represent a P2MP tree.
But they are different in some aspects such as contents, semantics.


Jeffrey

-----Original Message-----
From: pim <[e-mail]<mailto:[e-mail]>> On Behalf Of Bidgoli, Hooman (Nokia - CA/Ottawa)
Sent: Tuesday, January 12, 2021 10:07 AM
To: Stig Venaas <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

[External Email. Be cautious of content]


Hi Stig

And happy new year all!

Is PIM WG really the right place for this draft? After all this draft is trying to introduce a new segment type for the leaf router. I would imagine the work needs to start in the SPRING WG to understand what is a leaf segment type and understand the complications of this segment type in the bigger picture of segment routing.

Thanks
Hooman




-----Original Message-----
From: pim <[e-mail]<mailto:[e-mail]>> On Behalf Of Stig Venaas
Sent: Monday, January 11, 2021 2:54 PM
To: [e-mail]<mailto:[e-mail]>
Subject: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

Hi all

We discussed the draft draft-chen-pim-srv6-p2mp-path-01 in the last wg meeting. We did do an adoption call in the meeting, but we also would like to get input on the mailing list.

Please respond by January 25th whether you believe this document should be adopted.
The document can be found at
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense.com%2Fv3%2F__https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-chen-pim-srv6-p2mp-path-01__%3B!!NEt6yMaO-gk!VkCfh1h85mTSck3dXz4-Zl2ILoIBABk6FDbg8CYXKvteZ3OpsWdLRkneAwGrxmMp%24&amp;data=04%7C01%7Chuaimo.chen%40futurewei.com%7C41c897da80ec41896e9f08d8b72a5ebc%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637460739895968353%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=hnpkKlA9Rd3%2B9%2FGdveetHJB1ZBhEhVOhc0FCH6PDytk%3D&amp;reserved=0<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense.com%2Fv3%2F__https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-chen-pim-srv6-p2mp-path-01__%3B!!NEt6yMaO-gk!VkCfh1h85mTSck3dXz4-Zl2ILoIBABk6FDbg8CYXKvteZ3OpsWdLRkneAwGrxmMp%24&data=04%7C01%7Cmichael.mcbride%40futurewei.com%7C39d40656a24546dd773e08d8bb2d45ab%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637465150439801296%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=685QycQWUh6cfDeNPoOsUMTY%2BQHqaHBplm5PxAQELZE%3D&reserved=0>

Regards,
Stig

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Juniper Business Use Only

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