Subject: [bess] Questions on draft-sajassi-bess-evpn-l3vpn-multihoming

From: "Jeffrey (Zhaohui) Zhang" <[email-masked]>
Date: Wed, 4 Nov 2015 22:19:38 +0000

Hi,

I have a few questions:

   On the S-PEs, the pseudowires from the Access PEs are terminated onto
   VRFs, such that all pseudowires within a given redundancy set
   terminate on a single IP endpoint on the S-PEs. To achieve this, the
   S-PEs in a given Redundancy Group are configured with the same
   Anycast IP and MAC addresses on the virtual (sub)interface
   corresponding to the VRF termination point.

Is the virtual interface (like) an IRB interface?

   Since the S-PEs are running in EVPN single-active redundancy mode,
   the S-PEs would advertise an Ethernet AD route per vES with the
   single-active flag set per [RFC7432]. Since only the DF S-PE has its
   access pseudowire in Active state, only that device would establish
   an eBGP session with the CE and receive control and data traffic.

Will the IRB/virtual interface on a non-DF PE be up? I assume it is - even though the PW is not active. Would the non-DF PE keeps trying to establish the eBGP session with the CE? Would that cause issue to the session between CE and the DF PE?

   The
   DF S-PE advertises host prefixes that it receives, from the CE over
   the eBGP session, to other PEs in the EVI using EVPN route type-5,
   with the proper ESI set. Remote PEs learn the host prefixes and
   associate them with the ESI, using the advertising PE as the next-hop
   for forwarding.

Would he DF S-PE advertise other prefixes received on the eBGP session? I assume so but the text only says host prefixes.

   Other S-PEs in the same Redundancy Group as the advertising PE will
   receive the same EVPN route type-5 advertisement, and will recognize
   the associated ESI as a locally attached vES.

What is the RT that limits the routes to be imported only the PEs in the same redundancy group? Is it that all PEs in the same EVPN instance will import the routes? Or is it that different redundancy groups will have different EVPN instances? I assume it's latter (since we need one IRB interface for each redundancy group?).

   The withdrawal of the Ethernet
   Segment route serves as an indication to the backup S-PE to go active
   (i.e. act as a backup DF), and activate its pseudowires to the Access
   PE. The withdrawal of the Ethernet A-D route triggers a "mass
   withdraw" on the remote PEs: these PEs adjust their next-hop
   associated with the prefixes that were originally advertised by the
   failed PE to point to the "backup path" per [RFC7432].

Can you elaborate the procedure for the PEs to adjust their next-hop?

I don't see reference to draft-ietf-bess-evpn-vpws. Is that used at all?

Thanks.
Jeffrey

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From: "Ali Sajassi (sajassi)" <[email-masked]>
Date: Thu, 5 Nov 2015 02:16:16 +0000

Hi Jeffrey,

>Is the virtual interface (like) an IRB interface?

No IRB interface in this case. This is the virtual interface/sub-interface
address.

>Will the IRB/virtual interface on a non-DF PE be up? I assume it is -
>even though the PW is not active. Would the non-DF PE keeps trying to
>establish the eBGP session with the CE? Would that cause issue to the
>session between CE and the DF PE?

The backup PW will be in stand-by mode (not up) and thus there won¹t be a
eBGP session established between non-DF and the CE. Only when the non-DF
becomes DF, then eBGP session gets established.

>Would he DF S-PE advertise other prefixes received on the eBGP session? I
>assume so but the text only says host prefixes.

That¹s Correct. There will be other prefixes. We¹ll take care of it in the
next rev.

>What is the RT that limits the routes to be imported only the PEs in the
>same redundancy group? Is it that all PEs in the same EVPN instance will
>import the routes? Or is it that different redundancy groups will have
>different EVPN instances? I assume it's latter (since we need one IRB
>interface for each redundancy group?).

The RT will be the RT associated with the vES/ES.

>Can you elaborate the procedure for the PEs to adjust their next-hop?

Please refer to sections 8.4 and 14.1.1.

>I don't see reference to draft-ietf-bess-evpn-vpws. Is that used at all?

Evpn-vpws is not used but it can be used to reduce the PW provisioning to
only single-side.

Cheers,
Ali

---

From: "Jeffrey (Zhaohui) Zhang" <[email-masked]>
Date: Thu, 5 Nov 2015 02:31:58 +0000

Hi Ali,

> -----Original Message-----
> From: Ali Sajassi (sajassi) [mailto:[email-masked]]
> Sent: Thursday, November 05, 2015 11:16 AM
> To: Jeffrey (Zhaohui) Zhang <[email-masked]>; Samer Salam (ssalam)
> <[email-masked]>; Dennis Cai (dcai) <[email-masked]>
> Cc: [email-masked]
> Subject: Re: Questions on draft-sajassi-bess-evpn-l3vpn-multihoming
> 
> 
> Hi Jeffrey,
> 
> 

Whether it is an IRB interface or not, is the interface considered up (at layer 3) when the PW is in the stand-by mode?
I understand that the EBGP session won't be established, but will the standby PE try to establish it? Would that attempt cause trouble to the established session (assuming the CE will get messages from the standby PE via the primary PE)?

> The RT will be the RT associated with the vES/ES.

Will the vES/ES belong to a single EVPN instance only?

> Please refer to sections 8.4 and 14.1.1.

Part of my confusion came from the (wrong impression) that EVPN procedure is also used between the APE and SPE (for vpws). Now that it is not the case, would the same concept in this draft apply even if the CE is connected via regular ACs?

Thanks.
Jeffrey