Re: [bess] A question about the draft-wang-bess-sbfd-discriminator

["Wanghaibo (Rainsword)" <[e-mail]>]

Hi Greg,
       Thanks for you comments.
Yes, the resources will save at PE1 and PE2 as figure 1. This is a typical 3PE scenario.
       The service is like this:
+-----+    +-----+        +-----+
| UCE1|----| APE1|--------|SPE1 |,
+-----+    +-----+`      /+-----+ `.
                   `,  .'           `.+-----+
           ......    \/               | SCE1|
                     /\              `+-----+
                    `  `.          ,'
+-----+    +-----+,'     .+-----+ `
| uCEn|----| APEn|--------|SPE2 |`
+-----+    +-----+        +-----+
       There may be many Access PEs，used to access User CE. And they all multi-homed to a couple Servicc PE, SPE1 and SPE2.
       (shown as the PE1 and PE2 as figure 1)
        Access PE needs to detect Service PE’s reachability. Access PE creates SBFD session as an initiator, SPE as the reflector. This will save Service PEs’ resources.

Regards,
Haibo

From: Greg Mirsky [mailto:[e-mail]]
Sent: Tuesday, March 15, 2022 11:12 PM
To: Wanghaibo (Rainsword) <[e-mail]>
Cc: [e-mail]; BESS <[e-mail]>; rtg-bfd WG <[e-mail]>
Subject: Re: A question about the draft-wang-bess-sbfd-discriminator

Hi Haibo,
thank you for your expedient response. If I understand the scenario you're addressing, it is where a single PE with moderate resources is connected to a PE that acts as the edge device for the access network. To improve the quality of user experience, customer's PE is connected to a secondary PE that is used as a backup. You are concerned that maintaining two BFD sessions on the customer's PE might overload the resource-limited PE. But isn't that the PE that initiates S-BFD sessions toward two access network edge PEs in your draft? I think that the savings are on the side of these two PEs, not the subscriber's PE. Would you agree?

Regards,
Greg

On Tue, Mar 15, 2022 at 7:20 AM Wanghaibo (Rainsword) <[e-mail]<mailto:[e-mail]>> wrote:
Hi Greg,
       Thanks for your comments.
       The scenario you pointed out is a 4PE scenario, but in our solution, a large number of scenarios are based on 3PE.
In a 3PE scenario, deploying BFD wastes resources. A large number of single-homed PEs may be connected to the dual-homed PEs. The dual-homed PEs may not have enough resources to create BFD sessions.

Regards,
Haibo

From: Greg Mirsky [mailto:[e-mail]<mailto:[e-mail]>]
Sent: Tuesday, March 15, 2022 12:44 AM
To: Wanghaibo (Rainsword) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>; BESS <[e-mail]<mailto:[e-mail]>>; rtg-bfd WG <[e-mail]<mailto:[e-mail]>>
Subject: A question about the draft-wang-bess-sbfd-discriminator

Hi Haibo and the Authors,
thank you for updating the draft. I've read the new version and have a question about the use case presented in the document. There are three PEs with two of them providing redundant access to a CE. It appears that a more general case would be if both CEs use redundant connections to the EVPN. Asume, PE4 is added and connected to CE2. In that case, it seems reasonable that each PE is monitoring remote PEs, i.e., PE1 monitors PE3 and PE4, PE2 - PE3 and PE4, PE3 - PE1 and PE2, and PE4 - PE1 and PE2. So, now there are pairs of S-BFD sessions between PEs connected to CE1 and CE2 respectively. That seems like too many sessions and that number can be reduced if one uses BFD instead of S-BFD. Would you agree? To simplify operations, it might be helpful to use the technique described in draft-ietf-bfd-unsolicited<https://datatracker.ietf.org/doc/html/draft-ietf-bfd-unsolicited-09>. In the recent discussion of the draft on the BFD WG ML, the authors noted that they are working on extending the scope to include the multi-hop BFD.
Greatly appreciate your thoughts about the number of S-BFD sessions.

Regards,
Greg