Re: [bess] All-Active Multi-homing and Virtual Ethernet Segments: A Question

"Luc Andre Burdet (lburdet)" <> Tue, 25 September 2018 14:46 UTC

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From: "Luc Andre Burdet (lburdet)" <>
To: Alexander Vainshtein <>, "" <>
CC: Michael Gorokhovsky <>, Alexander Ferdman <>, Shell Nakash <>, "" <>
Thread-Topic: [bess] All-Active Multi-homing and Virtual Ethernet Segments: A Question
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Date: Tue, 25 Sep 2018 14:46:00 +0000
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Subject: Re: [bess] All-Active Multi-homing and Virtual Ethernet Segments: A Question
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Hi Sasha,

I agree the vES draft does not go in great detail about A/A PWs.

For A/A PWs terminating at peering PEs, the concept is similar to LAG, using static label at peering PEs:

  *   The CE sets up a single PW to remote endpoint to anycast IP1, Label1.
  *   PE1, PE2 set up a PW each to CE, using local static label Label1.
  *   PE1,PE2 adv IP1 as anycast IP towards CE-side
There will not be excessive MAC-moves since the CE sees only one pseudowire to a single remote—very similar to what is done for LAG on “real” links.

We can update the draft to be more descriptive—that draft needs a re-read anyways, the header on each page still reads “PBB-EVPN” ☺

Luc André


Luc André Burdet<>
Tel: +1 613 254 4814

Cisco Systems Canada Co. / Les Systemes Cisco Canada CIE<>

From: BESS <> on behalf of Alexander Vainshtein <>
Date: Tuesday, September 25, 2018 at 06:25
To: "" <>
Cc: Michael Gorokhovsky <>, Alexander Ferdman <>, Shell Nakash <>, "" <>
Subject: [bess] All-Active Multi-homing and Virtual Ethernet Segments: A Question

Dear authors of the EVPN Virtual Ethernet Segment<> draft,
My colleagues and I have a question pertaining to support of All-Active redundancy mode in EVPN that uses virtual Ethernet Segments.

Section 8.5 of RFC 7432<> says:

   If a bridged network is multihomed to more than one PE in an EVPN
   network via switches, then the support of All-Active redundancy mode
   requires the bridged network to be connected to two or more PEs using
   a LAG.

   If a bridged network does not connect to the PEs using a LAG, then
   only one of the links between the bridged network and the PEs must be
   the active link for a given <ES, VLAN> or <ES, VLAN bundle>.  In this
   case, the set of Ethernet A-D per ES routes advertised by each PE
   MUST have the "Single-Active" bit in the flags of the ESI Label
   extended community set to 1.

This restriction is easy to understand, since, with the All-Active multi-homing mode of an Ethernet Segment, a CE attached to such a segment potentially would receive traffic from all the PEs attached to this  segment. Since A CE that is part of a bridged network must learn MAC addresses of the received traffic, it would potentially experience continuous MAC Move events – with undesirable consequences.

The EVPN Virtual Ethernet Segment draft replaces Ethernet links (forming a “real” ES) with Ethernet PWs, and claims support of both Single-homed and multi-homed multi-homing modes. When I compare these claims with the quoted above statement from RFC 7432, I see two possibilities:

  *   Either a CE that is connected to an All-Active vES cannot be part of a bridged network (and thus would not do any MAC learning)
  *   Or  an extension of LAG that deals with Ethernet PWs instead of Ethernet links is required.

Could you please clarify which of these two options is correct?

Note: The draft includes Informative references to the two drafts that have been published as RFC 7432 and RFC 7623.


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