Re: [bess] EVPN MH: Backup node behavior in Primary Path Failure

[Jaikumar Somasundaram <[e-mail]>]

Thanks Mrinmoy.
Response in-lined.

From: Mrinmoy Ghosh (mrghosh) <[e-mail]>
Sent: Thursday, October 4, 2018 11:40 PM
To: Jaikumar Somasundaram <[e-mail]>; Rabadan, Jorge (Nokia - US/Mountain View) <[e-mail]>; [e-mail]
Cc: Jiang He <[e-mail]>; P Muthu Arul Mozhi <[e-mail]>
Subject: RE: [bess] EVPN MH: Backup node behavior in Primary Path Failure

Hi Jaikumar,

Backup failure can happen in multiple forms, Node down, Interface down etc.
There is no DF election timer on ES withdrawal, it should be carved immediately in Peering PEs.
[Jai] RFC 7432 does not mention anything about this.
<snip of section 8.5 of RFC 7432>
…
      In the case of link or port failure, the affected PE withdraws its
      Ethernet Segment route.  This will re-trigger the service carving
      procedures on all the PEs in the redundancy group.  For PE node
      failure, or upon PE commissioning or decommissioning, the PEs
      re-trigger the service carving.
<snip end>
DF election timer is manly when the ES is coming up (Node up, Interface up etc) to specify some.

Thanks,
Mrinmoy

From: BESS <[e-mail]<mailto:[e-mail]>> On Behalf Of Jaikumar Somasundaram
Sent: Thursday, October 4, 2018 8:39 AM
To: Rabadan, Jorge (Nokia - US/Mountain View) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: Jiang He <[e-mail]<mailto:[e-mail]>>; P Muthu Arul Mozhi <[e-mail]<mailto:[e-mail]>>
Subject: Re: [bess] EVPN MH: Backup node behavior in Primary Path Failure

Hi Jorge,

Yes, new DF will be identified after the new election.
Election process will need to wait for DF election timer period, say 3s or the configured timer period.
Until this DF election timer expiry and new DF is identified, the traffic towards CE coming to the node this PE
will get dropped. Please let me know if my understanding is right?

Thanks & Regards
Jaikumar S
From: Rabadan, Jorge (Nokia - US/Mountain View) <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, October 4, 2018 8:06 PM
To: Jaikumar Somasundaram <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: Jiang He <[e-mail]<mailto:[e-mail]>>; P Muthu Arul Mozhi <[e-mail]<mailto:[e-mail]>>
Subject: Re: [bess] EVPN MH: Backup node behavior in Primary Path Failure

Jai,

The new DF becomes DF because it re-runs DF election.
Thx
Jorge

From: Jaikumar Somasundaram <[e-mail]<mailto:[e-mail]>>
Date: Thursday, October 4, 2018 at 12:23 PM
To: "Rabadan, Jorge (Nokia - US/Mountain View)" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Cc: Jiang He <[e-mail]<mailto:[e-mail]>>, P Muthu Arul Mozhi <[e-mail]<mailto:[e-mail]>>
Subject: RE: [bess] EVPN MH: Backup node behavior in Primary Path Failure

In-line.

From: Rabadan, Jorge (Nokia - US/Mountain View) <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, October 4, 2018 3:33 PM
To: Jaikumar Somasundaram <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: Jiang He <[e-mail]<mailto:[e-mail]>>; P Muthu Arul Mozhi <[e-mail]<mailto:[e-mail]>>
Subject: Re: [bess] EVPN MH: Backup node behavior in Primary Path Failure

In-line.

Thx
Jorge

From: Jaikumar Somasundaram <[e-mail]<mailto:[e-mail]>>
Date: Thursday, October 4, 2018 at 11:28 AM
To: "Rabadan, Jorge (Nokia - US/Mountain View)" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Cc: Jiang He <[e-mail]<mailto:[e-mail]>>, P Muthu Arul Mozhi <[e-mail]<mailto:[e-mail]>>
Subject: RE: [bess] EVPN MH: Backup node behavior in Primary Path Failure

Thanks Jorge for the quick reply.
Please find further question below.

From: Rabadan, Jorge (Nokia - US/Mountain View) <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, October 4, 2018 1:52 PM
To: Jaikumar Somasundaram <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: Jiang He <[e-mail]<mailto:[e-mail]>>; P Muthu Arul Mozhi <[e-mail]<mailto:[e-mail]>>
Subject: Re: [bess] EVPN MH: Backup node behavior in Primary Path Failure

Hi,


Questions:
1.      Will the node in backup mode forward the packet to CE?

[JORGE] as soon as it becomes DF it can forward packets to the CE. The backup node will have to run DF election upon the ES route withdrawal from the primary. If AC-DF is enabled, it can also react to the withdrawal of AD routes from the primary PE.

[Jai] Does that mean if any packet comes to a node that is still in the backup mode will get dropped, before the new DF election is complete? Why cant this be used as FRR? Or what is the use case of having backup node(s)?

[JORGE2] when the primary node fails, ES and AD routes are withdrawn. The AD route withdrawal is an indication for remote nodes that they have to send traffic to the backup (for a given MAC) or to flush the MACs if there are more than 2 PEs in the ES. Around the same time or maybe earlier, the ES route withdrawal will make the backup PE take over as DF

[Jai] will it become DF without DF election? What if there is more than one PE in backup mode?

. So the overall convergence time will depend on how/when those two things happen in time. Only the DF PE can forward traffic. A non-DF can never forward traffic or there will be risk of duplicate packets.




2.      Will all the nodes in backup mode forward the packet before DF election?

[JORGE] Only the new DF can forward.



3. If they forward, how is duplicate packets handled, in this case?
[JORGE] see above.

My two cents..

Thanks.
Jorge



From: BESS <[e-mail]<mailto:[e-mail]>> on behalf of Jaikumar Somasundaram <[e-mail]<mailto:[e-mail]>>
Date: Thursday, October 4, 2018 at 10:03 AM
To: "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Cc: Jiang He <[e-mail]<mailto:[e-mail]>>, P Muthu Arul Mozhi <[e-mail]<mailto:[e-mail]>>
Subject: [bess] EVPN MH: Backup node behavior in Primary Path Failure


Hello Everyone,

Sorry if it is a duplicate. I repost this query as I did not receive any response yet.
(I was wondering if this mail already reached the group or not)


I have a question on Primary PE encountering a failure in EVPN multihoming

in single active mode.



RFC7432, section 14.1.1:

<snip>

   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.

</snip>



Questions:

1. Will the node in backup mode forward the packet to CE?

2. Will all the nodes in backup mode forward the packet before DF election?

3. If they forward, how is duplicate packets handled, in this case?



Please help me anwere these questions.



Thanks & Regards

Jaikumar S