Re: [bess] draft-mohanty-bess-evpn-bum-opt-00 - clarification on problem description

"Ali Sajassi (sajassi)" <> Thu, 22 March 2018 05:05 UTC

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From: "Ali Sajassi (sajassi)" <>
To: "Satya Mohanty (satyamoh)" <>, Sandy Breeze <>, "" <>
Thread-Topic: [bess] draft-mohanty-bess-evpn-bum-opt-00 - clarification on problem description
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Date: Thu, 22 Mar 2018 05:05:06 +0000
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Subject: Re: [bess] draft-mohanty-bess-evpn-bum-opt-00 - clarification on problem description
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Hi Satya,

As I mentioned earlier in another thread among the co-authors, we need to have a default mode of operation and for the default mode, the ESI MUST be factored-in the hash function (e.g.;, (vlan, ESI, PE’s IP address). Also, as discussed earlier we can capture in the draft the “option” for not factoring-in the ESI  (ESI=0 in the hash algorithm) – i.e., PEs in a redundancy group MAY all be configured to set ESI=0 in the hash algorithm.

BTW, do you have certain scenarios/use-cases in mind for setting ESI=0?


From: "Satya Mohanty (satyamoh)" <>
Date: Wednesday, March 21, 2018 at 3:16 PM
To: Cisco Employee <>, Sandy Breeze <>, "" <>
Subject: Re: [bess] draft-mohanty-bess-evpn-bum-opt-00 - clarification on problem description

We will take the feedback and revise the next version with the EVPN GW case as the primary use case.
Also, we will make it informational.

I need to make a mention again of what I spoke at the mic because I think it may not have been clear to everyone.
In the DF election framework draft, the weight is now a function of  the tuple(vlan, Esid, PE’s IP).
If we set the Esid to 0, then as long as each ES has the exact same set if vlans, the carving of vlans by the algorithm is the same.


From: BESS <<>> on behalf of "Ali Sajassi (sajassi)" <<>>
Date: Wednesday, March 21, 2018 at 6:27 PM
To: Sandy Breeze <<>>, "<>" <<>>
Subject: Re: [bess] draft-mohanty-bess-evpn-bum-opt-00 - clarification on problem description

Hi Sandy,

The key point in here is that the proposal is intended for EVPN GWs (and not PEs). By talking about PEs and NVEs at BESS yesterday, lot of people got confused. Although for EVPN GWs, this proposal makes better sense, for EVPN PEs, it doesn’t much because:

  1.  Vast majority (if not all) of TORs/PEs multi-homing are dual-homing which gives us zero benefit
  2.  Even for multi-homing with >2 PEs in the redundancy group, the chances of a PE not becoming a DF across all ES's in a BD is extremely low. We need to keep in mind that number of ES's are much larger than number of PEs !! And HRW algorithm in our df-framework draft takes into account the ES-id in its hash algorithm which means for the same BD, different PEs can become DF for different ES's !!
3) As soon as there is a stub node (e.g., a single-home CE) connected to any PE, then all bets are off and that PE needs to send IMET route and receive mcast traffic
4) As soon as there is a link/ES failure, then we will end-up with (3) above for dual-homing scenario and the PE with active link needs to send IMET route and receive mcast traffic
5) For mcast flow (*,G) or (S,G), the solution described in igmp-proxy draft  is the most optimal

So, I would suggest to do the following:

  1.  In the problem statement of the draft, capture the below use case clearly.
  2.  Change the name of the draft to “bum optimization for EVPN gateways”
  3.  Capture briefly why the proposal is not intended for EVPN PEs/NVEs because of the above reasons.


From: BESS <<>> on behalf of Sandy Breeze <<>>
Date: Wednesday, March 21, 2018 at 8:58 AM
To: "<>" <<>>
Subject: [bess] draft-mohanty-bess-evpn-bum-opt-00 - clarification on problem description

After some discussion, we acknowledge the problem description needs further clarification for this not to become too specific a use case.  Consider the following example of our existing live deployments;


The main points to articulate here are;

  *   PE[1..4] are at the boundary of an EVPN/MPLS domain (core side) and an EVPN/VXLAN domain (datacentre fabric side)
  *   They are responsible for L2VNI VTEP from ToR and MPLS L2VPN in core.
  *   From their point of view, 1 BD = 1 L2VNI (=1 ES).
  *   For any given DF type (modulo/HRW/etc) they distribute DF’s per-ES between them.
  *   Therefore, all nDF PE’s attract BUM for ES’s they’re not allowed to forward on and hence the waste of bandwidth in the EVPN core and cycles.

In our case, the solution we propose works very well.  We also showed this does no harm for the more typical EVPN-multihoming at the PE use case yesterday, which held up to technical scrutiny.