Re: [bess] Handshaking among PEs in an EVPN ES based on Paxos algorithm

[thomas.morin]

Hi,

Let me attempt at clarifying the exchange between the few of you.
My understanding is that:
- RFC7432 already does a good job of avoiding forwarding loops thanks to 
the split-horizon procedure that does not depend on DF election and has 
no transient state
- RFC7432 may have transient periods where the DF election state is not 
yet synchronized between the two peers:
  * the transient period correspond to BGP route propagation times  
(not to the DF election delay, although the wording in RFC 7432 could be 
made clearer)
  * during this period, if PEs do not block BUM traffic, some traffic 
may be lost
  * during this period, if PEs do not block BUM traffic, some traffic 
may be duplicated, but this is not considered very harmful and hence 
preferred to packet loss

The opinion, as I understand, that has been expressed by some is that 
the reduction of the transient period where duplicates may arise, is not 
worth the cost of an handshaking approach.

HTH,

-Thomas


26/03/2015 20:05, John E Drake :

Weiguo,

I guess I wasn’t clear.  I think you draft, for the reasons I have 
detailed, is a non-solution to a non-problem with tremendous control 
plane cost.

Yours Irrespectively,

John

*From:*Haoweiguo [mailto:haowei...@huawei.com]
*Sent:* Thursday, March 26, 2015 6:17 PM
*To:* John E Drake; Patrice Brissette (pbrisset)
*Cc:* Ali Sajassi (sajassi); bess@ietf.org
*Subject:* RE: [bess] Handshaking among PEs in an EVPN ES based on 
Paxos algorithm

Pls see below.

Thanks,

weiguo

------------------------------------------------------------------------

*From:*John E Drake [jdr...@juniper.net]
*Sent:* Friday, March 27, 2015 6:00
*To:* Haoweiguo; Patrice Brissette (pbrisset)
*Cc:* Ali Sajassi (sajassi); bess@ietf.org <mailto:bess@ietf.org>
*Subject:* RE: [bess] Handshaking among PEs in an EVPN ES based on 
Paxos algorithm

To recap,

We have established that your proposal is untenable because of its 
control plane load.

We have established that your proposal is based upon a flawed 
understanding of the DF election in RFC 7432.

[weiguo]: In ethernet world, traffic loop is serious than short timer 
traffic disruption. If you want to implement  transiet traffic loop 
process, i will modify my draft to solve your issue.

If i am the developer, i will prefer short timer traffic disruption 
based on current EVPN protocol.

What you are now arguing is that your draft prevents two or more PEs 
from being DF simultaneously. This is clearly nonsense.

[weiguo]: I will modify the draft problem statements, and use the same 
handshaking solution to solve it.

Furthermore, we have established that having two or more DFs for what 
even you admit is a brief transient leads to duplicate traffic, which 
is acceptable, but not loops, your assertion to the contrary.

[weiguo]: It is transient loop and traffic duplication issue.

Yours Irrespectively,

John

*From:*Haoweiguo [mailto:haowei...@huawei.com]
*Sent:* Thursday, March 26, 2015 5:37 PM
*To:* John E Drake; Patrice Brissette (pbrisset)
*Cc:* Ali Sajassi (sajassi); bess@ietf.org <mailto:bess@ietf.org>
*Subject:* RE: [bess] Handshaking among PEs in an EVPN ES based on 
Paxos algorithm

John,

As your understanding of the EVPN draft, the DF election mechanism has 
more serious side effect, it will have short time traffic loop,i.e., 
dual DF PEs will exist for a short time. I think dual DF PEs is 
absolutely not tolerated, because native ethernet header has no TTL, 
up to several hundred ms traffic loop normally not tolerated in 
commertial networks.

As your understanding, the PEs should do as following:

1. Accurate timer sync. NTP accuracy is bad, 1588v2 is good but have 
rarely deployment.

Assuming PE1,PE2 and PE3 have consistent timer clock, when PE3 joins 
ESI and trigger DF re-election. When reception timer expires:

PE1 upgrades to DF PE.

After reception timer+ ES route transmission timer:

PE2 downloads to non-DF PE.

So in timer clock sync case, dual DF PEs will exist at least 
transmission timer.

If NTP is used for timer sync, because it has bad accuracy, dual DF 
PEs will exist more longer timer.

So as your understanding for DF election, the drawback is more clear.

Thanks,

weiguo

------------------------------------------------------------------------

*From:*John E Drake [jdr...@juniper.net]
*Sent:* Friday, March 27, 2015 4:41
*To:* Haoweiguo; Patrice Brissette (pbrisset)
*Cc:* Ali Sajassi (sajassi); bess@ietf.org <mailto:bess@ietf.org>
*Subject:* RE: [bess] Handshaking among PEs in an EVPN ES based on 
Paxos algorithm

Weiguo,

We have already established that your proposal is untenable because of 
its control plane load.

What we are now discussing is that your proposal is based upon a 
misunderstanding of the algorithm in RFC 7432.  You are assuming that 
PE1 will advertise an ES route and then wait for the configured 
interval before performing the DF election while PE2 and PE3 will 
perform the DF election as soon as they receive the ES route from PE1. 
This is not what RFC 7432 says.

Rather, what is says is that the advertisement of the ES route by PE1 
and its receipt by PE2 and PE3 causes all three PEs to start the 
configured interval timer  - “3. When the timer expires, each PE 
builds an ordered list of the IP addresses of all the PE nodes 
connected to the Ethernet segment (including itself), in increasing 
numeric value.”

Yours Irrespectively,

John

*From:*Haoweiguo [mailto:haowei...@huawei.com]
*Sent:* Thursday, March 26, 2015 3:26 PM
*To:* John E Drake; Patrice Brissette (pbrisset)
*Cc:* Ali Sajassi (sajassi); bess@ietf.org <mailto:bess@ietf.org>
*Subject:* RE: [bess] Handshaking among PEs in an EVPN ES based on 
Paxos algorithm

Pls read my detail replies to Satya. If you still can't catch it, pls 
read my draft and EVPN base protocol,  thanks

weiguo

------------------------------------------------------------------------

*From:*John E Drake [jdr...@juniper.net]
*Sent:* Friday, March 27, 2015 1:28
*To:* Patrice Brissette (pbrisset)
*Cc:* Haoweiguo; Ali Sajassi (sajassi); bess@ietf.org 
<mailto:bess@ietf.org>
*Subject:* Re: [bess] Handshaking among PEs in an EVPN ES based on 
Paxos algorithm

I think Patrice is correct.  Your proposal doesn't solve the problem 
and it does so at huge cost.

Sent from my iPhone


On Mar 26, 2015, at 10:34 AM, Patrice Brissette (pbrisset) 
<pbris...@cisco.com <mailto:pbris...@cisco.com>> wrote:

    Weiguo,

    I’m not sure I’m following here.

    Don’t you have the same issue with your handshaking mechanism?

    If you don’t know your peer, how can you handshake?

    Regards,

    Patrice

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    pbris...@cisco.com <mailto:pbris...@cisco.com>
    Phone: *+1 613 254 3336*

        

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    *From: *Haoweiguo <haowei...@huawei.com <mailto:haowei...@huawei.com>>
    *Date: *Thursday, March 26, 2015 at 10:24 AM
    *To: *Patrice Brissette <pbris...@cisco.com
    <mailto:pbris...@cisco.com>>, John E Drake <jdr...@juniper.net
    <mailto:jdr...@juniper.net>>, Ali Sajassi <saja...@cisco.com
    <mailto:saja...@cisco.com>>, "bess@ietf.org
    <mailto:bess@ietf.org>" <bess@ietf.org <mailto:bess@ietf.org>>
    *Subject: *RE: [bess] Handshaking among PEs in an EVPN ES based on
    Paxos algorithm

        Hi Patrice,

        Up to reception timer traffic disruption in transient phase is
        one of the issues.

        Thanks,

        weiguo

        ------------------------------------------------------------------------

        *From:*Patrice Brissette (pbrisset) [pbris...@cisco.com
        <mailto:pbris...@cisco.com>]
        *Sent:* Thursday, March 26, 2015 20:54
        *To:* Haoweiguo; John E Drake; Ali Sajassi (sajassi);
        bess@ietf.org <mailto:bess@ietf.org>
        *Subject:* Re: [bess] Handshaking among PEs in an EVPN ES
        based on Paxos algorithm

        Weiguo,

        You mention "But if your draft have not solved all issues”,

        Can you explain what Satya’s draft is not solving?

        Regards,

        Patrice

        Image removed by sender.

        *Patrice Brissette*
        TECHNICAL LEADER.ENGINEERING

        pbris...@cisco.com <mailto:pbris...@cisco.com>
        Phone: *+1 613 254 3336*

                

        *Cisco Systems Canada Co. / Les Systemes Cisco Canada CIE*
        Canada
        Cisco.com <http://www.cisco.com/global/CA/>

                

        Image removed by sender.Think before you print.

        This email may contain confidential and privileged material
        for the sole use of the intended recipient. Any review, use,
        distribution or disclosure by others is strictly prohibited.
        If you are not the intended recipient (or authorized to
        receive for the recipient), please contact the sender by reply
        email and delete all copies of this message.

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        *From: *Haoweiguo <haowei...@huawei.com
        <mailto:haowei...@huawei.com>>
        *Date: *Wednesday, March 25, 2015 at 10:38 PM
        *To: *John E Drake <jdr...@juniper.net
        <mailto:jdr...@juniper.net>>, Ali Sajassi <saja...@cisco.com
        <mailto:saja...@cisco.com>>, "bess@ietf.org
        <mailto:bess@ietf.org>" <bess@ietf.org <mailto:bess@ietf.org>>
        *Subject: *Re: [bess] Handshaking among PEs in an EVPN ES
        based on Paxos algorithm

            Hi John,

             Firstly i think EVPN community should reach consensus on
            the issues of current DF election mechanism. All these
            issues should be resolved in a single new DF election
            draft,rather than in multiple separate drafts. If your
            draft can solve all these issues and stable, i have no
            question for its progressing. But if your draft have not
            solved all issues, i think it had better combine with
            other drafts to provide a comprehensive solution. I think
            the issues listed in draft-rabadan-bess-evpn-ac-df-01 and
            draft-hao-bess-evpn-df-handshaking-00 is valid, it should
            be resolved. So i think although your new Hash algorithm
            for DF election is good, it only includes partial
            enhancements, maybe it still needs some time for consensus.

            Thanks,

            weiguo

            
------------------------------------------------------------------------

            *From:*John E Drake [jdr...@juniper.net
            <mailto:jdr...@juniper.net>]
            *Sent:* Thursday, March 26, 2015 7:16
            *To:* Haoweiguo; Ali Sajassi (sajassi); bess@ietf.org
            <mailto:bess@ietf.org>
            *Subject:* RE: [bess] Handshaking among PEs in an EVPN ES
            based on Paxos algorithm

            Weiguo,

            Your proposal introduces a control plane processing load
            that is O(#EVIs * PEs) per DF election and given that
            there can be 4K EVIs per ES, this looks like a
            **substantial** load. Furthermore,

            you can’t  use the ES route to co-ordinate DF election
            because you would need to carry your new extended
            community for each EVI and they would not all fit.  You
            also can’t use the Per EVI Ethernet AD route because that
            is processed by all PEs in the EVI.

            I think that from a practical perspective the new DF
            election proposed in Satya’s draft is sufficiently stable
            that it renders your draft moot, even if it could be made
            to work.

            Yours Irrespectively,

            John

            *From:*BESS [mailto:bess-boun...@ietf.org] *On Behalf Of
            *Haoweiguo
            *Sent:* Wednesday, March 25, 2015 5:34 PM
            *To:* Ali Sajassi (sajassi); bess@ietf.org
            <mailto:bess@ietf.org>
            *Subject:* Re: [bess] Handshaking among PEs in an EVPN ES
            based on Paxos algorithm

            Hi Ali,

            Thanks for your information. I scanned through this draft,
            it really introduces inter-chassis message for DF election
            handshaking, the requirements in this draft is to
            eliminate transiet Loop and traffic duplication. Current
            EVPN DF election mechanism already eliminated loop and
            traffic duplication by configuring long reception timer on
            each multi-homed PE, but up to reception timer traffic
            disruption issue still exist. EVPN for DCI is an important
            use case for EVPN, up to reception timer traffic
            disruption can't be tolerated for service providers, it
            should be improved.

            Also for accuracy, i think handshaking state machine on
            each multi-homed PE is also needed. From solution
            perspective, in my draft, no inter-chassis message is
            introduced, only one new extended community is introduced,
            i think the process is comparatively simple than your
            following draft.

            Current EVPN DF election has some drawbacks, so there are
            three new drafts about DF election emerged. I think BESS
            WG can consider these three drafts in global view, a
            single,comprehensive new DF election draft is hoped.

            thanks.

            Thanks,

            weiguo

            
------------------------------------------------------------------------

            *From:*BESS [bess-boun...@ietf.org
            <mailto:bess-boun...@ietf.org>] on behalf of Ali Sajassi
            (sajassi) [saja...@cisco.com <mailto:saja...@cisco.com>]
            *Sent:* Thursday, March 26, 2015 0:21
            *To:* bess@ietf.org <mailto:bess@ietf.org>
            *Subject:* [bess] Handshaking among PEs in an EVPN ES
            based on Paxos algorithm

            FYI- First published July 4, 2011

            
https://datatracker.ietf.org/doc/draft-sajassi-l2vpn-evpn-segment-route/

            -Ali



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