Hi all,
I have some concerns regarding the Control Plane procedures for the Symmetric
EVPN IRB as described in Sections 5.1, 5.2 and 5.4 of RFC
9135<https://datatracker.ietf.org/doc/html/rfc9135>..
In the context of EVPN-MPLS these procedures say that (only relevant parts of
the spec are mentioned):
1. The egress PE that has contains a Symmetric ERVPN IRB and has locally
learned an IP-->MAC pair (e.g., via an ARP or NDP message), from an AC that
belongs to the BD used by this IRB, advertises an RT-2 for this pair as
following:
* The Label2 field in the NLRI of this RT-2 is set to the value that
identifies the local IP-VRF to which the Symmetric IRB in question belongs
* The Export Route Targets of both the MAC-VRF that contains the BD in
question and the IP-VRF that contains the IRB in question MUST be attached to
this RT-2
2. The ingress PE that supports Symmetric IRB and receives such an RT-2:
* Identifies the local IP-VRF with a matching Import Route Target
* Imports IP address in the NLRI of this RT-2 into this IP-VRF, i.e.,
installs a labeled host route in the RIB of this IP-VRF as following:
i. The
destination of this route is a /32 (for IPv4) or a /128 (for IPv6) prefix based
on the IP address in the NLRI of RT-2 in question
ii. The
next hop of this route is the next hop address of RT-2 in question
iii. The label
of this route is the value carried in the Label2 field of this RT-2
* Encapsulates locally received IP packets with this destination IP
address using this route.
The above rules do not make any exceptions for the special case of IP address
in the IP-->MAC pair in question being a link-local IPv6 address.
My guess is that import of link-local IPv6 addresses by IP-VRFs in "remote" PEs
is meaningless and potentially harmful since IPv6 packets with link-local
Source or Destination IPv6 addresses are not routable (see Section 2.5.6 of RFC
4291<https://www.rfc-editor.org/rfc/rfc4291.html#section-2.5.6>). At the same
such IPv6-->MAC pairs MUST be used, say, to update the Neighbor Cache of local
instantiations of anycast EVPN IRB in PEs that contain local instantiations of
the same BD.
One way to address this special case could be by omitting Export Route Targets
of IP-VRF that contains a Symmetric IRB when advertising RT-2 for locally
learned IPv6-->MAC pairs with link-local IPv6 addresses in the NRLI.
Your timely feedback would be highly appreciated.
Regards, and lots of thanks in advance,
Sasha
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