Re: [bess] FW: Regarding the Alias label usage in EVPN Multihoming

[Muthu Arul Mozhi Perumal <[e-mail]>]

Thanks, Sasha.

Is my understanding for the all-active case correct?

It should be noted that in the scenario described by Chalapathi, only PE1
advertises the MAC/IP route for MAC1. PE2 and PE3 advertise only alias
labels..

Regards,
Muthu

On Thu, Mar 7, 2019 at 3:40 PM Alexander Vainshtein <
[e-mail]> wrote:

>
>
> Muthu and all,
>
> Quoting from Section 14.1.1 “Single-Active Redundancy Mode”  of RFC 7432:
>
>
>
>    If the primary PE encounters a failure, it MAY withdraw its set of
>
>    Ethernet A-D per ES routes for the affected ES prior to withdrawing
>
>    its set of MAC/IP Advertisement routes.
>
>
>
>    If there is only one backup PE for a given ES, the remote PE MAY use
>
>    the primary PE's withdrawal of its set of Ethernet A-D per ES routes
>
>    as a trigger to update its forwarding entries, for the associated MAC
>
>    addresses, to point towards the backup PE.  As the backup PE starts
>
>    learning the MAC addresses over its attached ES, it will start
>
>    sending MAC/IP Advertisement routes while the failed PE withdraws its
>
>    routes.  This mechanism minimizes the flooding of traffic during
>
>    fail-over events.
>
>
>
>    If there is more than one backup PE for a given ES, the remote PE
>
>    MUST use the primary PE's withdrawal of its set of Ethernet A-D per
>
>    ES routes as a trigger to start flooding traffic for the associated
>
>    MAC addresses (as long as flooding of unknown unicast packets is
>
>    administratively allowed), as it is not possible to select a single
>
>    backup PE.
>
>
>
> So there are actually three sub-cases in the single-active redundancy mode
> use case:
>
> 1.       The single-active multi-homed ES has been advertised by exactly
> two PEs. In this case withdrawal of the per-ES Ethernet A-D route by the
> primary PE may result in other PEs sending the unicast traffic for MAC
> addresses  learned from this ES to the secondary PE using the alias labels
> advertised for the corresponding EVI in the per-EVI Ethernet A-D routes.
>
> 2.       The  single-active multi-homed ES has been advertised by three
> or more PEs, and flooding of unknown unicast is allowed. In this case
> withdrawal of the per-ES Ethernet A-D route by the primary PE MUST result
> in flooding of the unicast traffic with unlearned MAC addresses using the
> common scheme for BUM traffic. The Aliasing labels are not relevant for
> this use case.
>
> 3.        The  single-active multi-homed ES has been advertised by three
> or more PEs, and flooding of unknown unicast is not allowed. In this case
> withdrawal of the per-ES Ethernet A-D route by the primary PE MUST in just
> local flooding of the unicast traffic with unlearned MAC addresses.
>
>
>
> Hope this helps.
>
> My 2c,
>
> Sasha
>
>
>
> Office: [phone]
>
> Cell:      [phone]
>
> Email:   [e-mail]
>
>
>
> *From:* BESS <[e-mail]> *On Behalf Of *Muthu Arul Mozhi
> Perumal
> *Sent:* Thursday, March 7, 2019 8:53 AM
> *To:* Luc Andre Burdet (lburdet) <[e-mail]>
> *Cc:* chalapathi andhe <[e-mail]>; Sean Wu <
> [e-mail]>; Jaikumar Somasundaram <
> [e-mail]>; [e-mail];
> [e-mail]
> *Subject:* Re: [bess] FW: Regarding the Alias label usage in EVPN
> Multihoming
>
>
>
> My understanding:
>
>
>
> For the single-active case in the diagram below, when PE4 receives the A-D
> per ES route withdraw it won't know whether PE2 or PE3 will become the new
> primary/DF for the <ES, VLAN>, so it will start flooding the traffic
> destined to MAC1. Then either PE2 or PE3 will become the new primary/DF for
> the <ES, VLAN> and advertise the MAC/IP route for MAC1. PE4 will then start
> sending the traffic destined to MAC1 to the new primary.
>
>
>
> For the all-active case, when PE4 receives the A-D per ES route withdraw
> it will update the nexthop list for MAC1 by removing PE1 from that list.
> PE4 will then load balance the traffic destined to MAC1 by send it to PE2
> and PE3 using alias label.
>
>
>
> Regards,
>
> Muthu
>
>
>
> On Wed, Mar 6, 2019 at 7:51 PM Luc Andre Burdet (lburdet) <
> [e-mail]> wrote:
>
> Hi Chalu,
>
>
>
> Please read 7432 s.8.4: in single-active it is not an aliasing
> label/procedure but a backup-path procedure.
>
> It will answer your questions (both, actually).
>
>
>
> There is no flooding once the MAC is learnt & distributed: cf. that’s the
> point.
>
>
>
>
>
> [image:
> http://www.cisco.com/c/dam/m/en_us/signaturetool/images/banners/standard/09_standard_graphic.png]
>
> *Luc André Burdet*
>
> [e-mail]
>
> Tel: *[phone]*
>
> Cisco Systems Canada Co. / Les Systemes Cisco Canada CIE
>
> Cisco.com <http://www.cisco.com/web/CA/>
>
>
>
>
>
> *From: *BESS <[e-mail]> on behalf of chalapathi andhe <
> [e-mail]>
> *Date: *Wednesday, March 6, 2019 at 04:15
> *To: *"[e-mail]" <[e-mail]>
> *Cc: *Sean Wu <[e-mail]>, Jaikumar Somasundaram <
> [e-mail]>, "[e-mail]" <
> [e-mail]>
> *Subject: *Re: [bess] FW: Regarding the Alias label usage in EVPN
> Multihoming
>
>
>
>
>
>
>
> Hi All,
>
>
>
> Can you please help us on the following issue.
>
> In the following diagram, PE1, PE2, PE3 are connected to the same ES [ES1]
> in Single active mode, and PE4 is a remote PE.
>
> Let’s say PE1 is advertising the MAC1 route, PE4 will install the MAC1
> with the PE1 as primary path with MAC Label,
>
> and PE2, PE3 as backup with the Alias Label. Now if the PE1 to CE1 link
> goes down, then PE1 withdraw the EAD/ES route
>
> which will be processed by PE4.
>
> Now what should the forwarding state at PE4 ?, PE4 should update the
> forwarding state of MAC1 with the PE2, PE3 Alias label
>
> and any traffic destined to MAC1 should be flooded to PE2, PE3 with the
> Alias labels ?
>
> Or packet should be flooded to PE2, PE3 with the Flood labels ? Or should
> it be some other method ?
>
>
>
> In similar if the ES is operating in all active mode, what should be the
> forwarding state at PE4 ?
>
> PE4 should update the forwarding state of MAC1 with the PE2, PE3 Alias
> label
>
> and any traffic destined to MAC1 should be sent to either PE2 or PE3 with
> the Alias labels [ not flood to both] ?
>
> Or packet should be flooded to PE2, PE3 with the Flood labels  or Alias
> Label ?
>
> Or should it be some other method ?
>
>
>
>
>
> [image: cid:1695247dcc04ce8e91]
>
>
>
>
>
> Thanks,
>
> Chalapathi.
>
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