Dear authors of
draft-wang-bess-evpn-control-word<https://tools.ietf.org/html/draft-wang-bess-evpn-control-word-00>,
I have doubts regarding at least one of the approaches for negotiating the CW
usage in the EVPN encapsulation between egress and ingress PE that is defined
in the draft.
In the case when the egress PE can receive EVPN-encapsulated packets both with
and without CW, the draft seems to propose (as one of the possibilities)
advertisement of two EVPN routes for each ES or MAC/IP pair:
- One of these routes would use the CW Capability to indicate that it
refers to the EVPN encapsulation that uses the CW, and would carry the
appropriate label in its NLRI
- The other route would not use the CW Capability to indicate that it
refers to the EVPN encapsulation that does not use the CW, and carry a
different label in its NLRI
The ingress PE that accepts these routes would then use one of them based on
its own ability to use the CW (or lack thereof), and use the corresponding
label it its EVPN encapsulation, while the DP in the egress PW would infer
presence or absence of the CW from the received EVPN application label.
Unfortunately, I do not think that this can work because, as per RFC
7432<https://tools.ietf.org/html/rfc7432>, labels in the labeled NLRI of EVPN
routes are not part of the route key for the purpose of the BGP route key
processing, while the label is treated just as the BGP attribute. This means
that, unless some form of BGP multi-path is enabled in the ingress PE (and in
all RRs on the way between the egress PE and ingress PE) for the L2VPN/EVPN
AFI/SAFI, only one of these routes will be selected by the BGP selection
process.
Did I miss something substantial here?
Regards, and lots of thanks in advance,
Sasha
Office: +972-39266302
Cell: +972-549266302
Email: [email protected]
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