Re: [bess] Query/comments on draft-ietf-bess-evpn-lsp-ping-05

["Dikshit, Saumya" <[e-mail]>]

Hi Parag,

Please see inline. Let me know your thoughts.

Thanks
Saumya.

From: Parag Jain (paragj) [mailto:[e-mail]]
Sent: Wednesday, September 8, 2021 11:43 PM
To: Dikshit, Saumya <[e-mail]>om>; [e-mail]; [e-mail]
Cc: [e-mail]
Subject: Re: Query/comments on draft-ietf-bess-evpn-lsp-ping-05

Hi Saumya

Pls see inline.

From: "Dikshit, Saumya" <[e-mail]<mailto:[e-mail]>>
Date: Tuesday, September 7, 2021 at 3:22 PM
To: "Parag Jain (paragj)" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Cc: "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Subject: RE: Query/comments on draft-ietf-bess-evpn-lsp-ping-05

Hi Parag,

Thanks for the response. I have few bullets on the same.
Please help clarify and if there is a need to call them out explicitly.


  1.  “Consistency checkers” feature-set does validates the CP-DP parity and can be leveraged via management interface to the box.
     *   Do you imply the consistency check between protocol RIB and the dataplane FIB, Or the consistency between Software FIB (slow path) and the LC-FIB
Paragj> CP would mean BGP/EVPN/RIB which ever CP component has the info included in the sub-TLVs.
[SD] I am little unclear, as to how running the Sub-TLV parameters through the RIB, will ensure that this RIB entry (NLRI) was CHOSEN as the FIB entry.
Essentially, the RIB entry mapping to the Sub-TLV, has to contend with other RIB entries and also with same route published by other protocols (or instances of protocol), eventually get picked as FIB entry.  Lsp ping to the sub-tlv may pan out differently in RIB and in FIB. But as I understand, that is not the purpose of this reachability check defined in this draft.
We should call out this out specifically in the document or stick to validating the datapath.
Both RIB and FIB validation (leading to successful echo response), may not indicate that right RIB and FIB are consistent with respect to sub-tlv being carried.
I suggest that we keep lsp ping to just the data plane validation. Consistency-check will require lot of compute (might need a complete path calculation of BGP-EVPN), to indicate the consistency. Good to know if there are reference implementations optimizing this already.
This is one more reason to use wild card.


  1.  Parameters such as RD, shall not make it to the DP and their presence is restricted to the NLRI (entries/tables) in the protocol RIB.
     *   In case the RIB specific parameters need validation, then on receive side processing of ping, should run it through the RIB and FIB both ?
Paragj> yes.

     *   In case it’s just the dataplane validation (which I can gather from this draft), then RIB validation is not required and RD’s  can carry “don’t care”.
  1.  If a need be, to perform “reachability-check to a tenant vrf (EVI) on remote NVE”, for which no route has been published yet ?
Paragj> only vrf-existence is not checked by lsp ping.
[SD] That’s a good solution to have. I have mentioned the use-case in below email.
I propose that we leverage the existing “EVPN IP Prefix Sub-TLV”, with appropriate values (may be wild-card/don’t care) to realize this.

Thanks
Parag

as I mentioned in #2 of below email

     *   Is it possible to achieve that with lsp-ping check with existing sub-TLVs without “wild-card/don’t-care”

Thanks
Saumya.

From: Parag Jain (paragj) [mailto:[e-mail]]
Sent: Tuesday, September 7, 2021 11:56 PM
To: Dikshit, Saumya <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>
Subject: Re: Query/comments on draft-ietf-bess-evpn-lsp-ping-05

Hi Saumya

The remote PE router processing the lsp ping packet, does consistency checks between data plane and control plane. RD, ESI fields along with other fields defined in the sub-tlvs are used for that purpose. Wildcard/don’t care values for these fields will defeat the purpose of DP-CP consistency checks.

Thanks
Parag

From: "Dikshit, Saumya" <[e-mail]<mailto:[e-mail]>>
Date: Thursday, September 2, 2021 at 1:42 PM
To: "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Cc: "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Subject: Query/comments on draft-ietf-bess-evpn-lsp-ping-05
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Resent-Date: Thursday, September 2, 2021 at 1:42 PM

[sending the queries in a different email with changed subject line]

Hello Authors of draft-ietf-bess-evpn-lsp-ping draft,

I have following queries regarding this draft:

>>>> Do we intend-to-use/call-out-usage-of “wild-card/don’t-care” values for attributes carried in the sub-TLVs ?
For example, If the admin intends  to check the reachability to host (MAC_X/IP_X) published (in route-type-2)  by remote PE.
The remote PE learnt it locally over ESI_X against Vlan X (mapped to BD_XYZ).

Is it possible, that the “EVPN MAC sub-tlv”  can carry the “Route Distinguisher” and “Ethernet Segment Identifier” as don’t care.

>>>> Another caseto handle would be test the reachability to tenant-VRF VRF_X (with EVPN mapped EVI) configured on the remote PE, PE1.
VRF_X has no active IP/IPv6 interface configured and its sole usage is to obtain the leaked (via IVRL) routes from other VRFs (non-EVPN) and PE1 published this to other peers via EVPN control plane. Till the first prefix (learnt ) route is published (Route Type 5) by PE1 for the EVI (mapped to VRF_X), the tunnels will not be provisioned on other PEs.
In order to test the reachability to VRF_X (on PE1) from another PEs, let’s say, PE2 or a centralized-controller (which can emulate/supports MPLS),

It may need to carry all/subset-of attributes with “don’t-care/wild-card” in “EVPN IP Prefix Sub-TLV”.


Please let know your thoughts on above.

Thanks
Saumya.