[bess] A question pertaining to validation of LSP Ping Echo requests in draft-ietf-bess-evpn-lsp-ping-08

[Alexander Vainshtein <[e-mail]>]

Hi all,
My colleagues and I have a question about the validation rules for LSP Ping Echo Requests associated with EVPN Type 2 routes in draft-ietf-bess-evpn-lsp-ping-08<https://datatracker.ietf.org/doc/html/draft-ietf-bess-evpn-lsp-ping-08>.

The problematic text in Section 4.1 of the draft says:

   The LSP Echo Request is sent using the EVPN MPLS label(s) associated
   with the MAC/IP Advertisement route announced by a remote PE and the
   MPLS transport label(s) to reach the remote PE.  When remote PE
   processes the received LSP Echo Request packet, the remote PE
   validates the MAC state if the MAC/IP Sub-TLV contains only MAC
   address.  If the MAC/IP Sub-TLV contains both MAC and IP address, the
   PE validates the ARP/ND state.

Here are our questions:

  1.  Suppose that some MAC address:
     *   Has been learned by the intended egress PE from the Data Plane from an All-Active MH ES and advertised in a MAC-only route EVPN Type 2 route
     *   An EVPN Type 2 route for some IP→MAC pair with the same MAC address has been advertised by another PE attached to the same All-Active MH ES
     *   An LSP Ping Echo request with the IP→MAC pair in question and the label that has been advertised by the intended egress PE in the Label1 field of an EVPN Type 2 route for the MAC address in question is received
What is the expected result of the validation taking into account that the egress PE has not ever advertised an EVPN Type 2 route for the IP→MAC pair in question?

  1.  Suppose that:
     *   Some MAC address as been learned by the egress PE only via the control plane (ARP/ND) and advertised In an EVPN Type 2 route for an IP→MAC pair
     *   A MAC-only LSP Ping request for the MAC address in question with the label advertised in the Label1 field of the EVPN Type 2 route for an IP→MAC pair in question has been received
What is the expected result of the validation taking into account that the egress PE has not advertised any MAC-only routes for the MAC address in question?

  1.  Suppose that:
     *   We are dealing with a BD that is used by a Symmetric EVPN IRB
     *   Some MAC address as been learned by the egress PE only via the control plane (ARP/ND)  and has been advertised In an EVPN Type 2 route for an IP→MAC pair with Label2 field present
     *   A MAC-only LSP Ping request for the MAC address in question with the label advertised in the Label2field of the EVPN Type 2 route for an IP→MAC pair in question has been received
What is the expected result of the validation?

  1.  Same as #3 above, but the LSP Ping request is for the IP→MAC pair in question and with the label advertised in the Label2 field of the EVPN Type 2 route for an IP→MAC pair in question?

>From my POV the simplest way to answer all these questions would be to say that the information and the label in the LSP Ping Echo request should be validated vs. the set of EVPN Type 2 routes advertised by the egress PE and succeed (yielding return code 3) only in the case of an exact match. Scenarios described in #1, #2 and #3 above could be treated as partial matches and yielding some new return codes while scenario 4 would be treated as success.

Your timely feedback would be highly appreciated.

Regards, and lots of thanks in advance,
Sasha


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