Adam Roach's No Objection on draft-ietf-bfd-vxlan-09: (with COMMENT)

[Adam Roach via Datatracker <[e-mail]>]

Adam Roach has entered the following ballot position for
draft-ietf-bfd-vxlan-09: No Objection

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COMMENT:
----------------------------------------------------------------------

Thanks for the work that everyone has put into this document. I have
a couple of relatively important, related comments that should be
taken into account prior to publication.

---------------------------------------------------------------------------

§3:

>  As per Section 4, the inner destination IP address SHOULD be set to
>  one of the loopback addresses (127/8 range for IPv4 and
>  0:0:0:0:0:FFFF:7F00:0/104 range for IPv6).

Please consider reformatting this IPv6 address according to the recommendations
of RFC 5952 (paying particular attention to sections 4.2.1, 4.3, and 5):

::ffff:127.0.0.0/104

It's also worth noting that, as a practical matter, modern operating systems do
not seem to bind to anything in the IPv4-mapped range assigned to IPv4 loopback:

Linux:

  ~$ ping6 ::ffff:127.0.0.1
  PING ::ffff:127.0.0.1(::ffff:127.0.0.1) 56 data bytes
  ^C
  --- ::ffff:127.0.0.1 ping statistics ---
  14 packets transmitted, 0 received, 100% packet loss, time 13316ms

MacOS:

  ~$ ping6 ::ffff:127.0.0.1
  PING6(56=40+8+8 bytes) ::ffff:127.0.0.1 --> ::ffff:127.0.0.1
  ping6: sendmsg: Invalid argument
  ping6: wrote ::ffff:127.0.0.1 16 chars, ret=-1


It is not clear to me whether this poses an issue for your intended usage.

In any case, please do not refer to ::ffff:127.0.0.0/104 as "loopback
addresses": IPv6 has only one loopback address defined (::1). The range
you cite is best described as "IPv4-mapped IPv4 loopback addresses."
Alternately -- and this is probably better -- use "::1/128" instead of
"::ffff:127.0.0.0/104" for the inner IP header destination address.

As an aside, I share Benjamin's unease around the use of loopback addresses
in this fashion. It may be worth noting that IETF protocols can reserve
addresses in the 192.0.0.0/24 and 2001::/23 blocks if necessary, and such
reserved addresses won't ever correspond to a valid destination.

(There is corresponding text in section 4 that all of the preceding pertains
to as well)

---------------------------------------------------------------------------

§9:

>  This document recommends using an address from the Internal host
>  loopback addresses (127/8 range for IPv4 and
>  0:0:0:0:0:FFFF:7F00:0/104 range for IPv6) as the destination IP
>  address in the inner IP header.  Using such address prevents the
>  forwarding of the encapsulated BFD control message by a transient
>  node in case the VXLAN tunnel is broken as according to [RFC1812]:
>
>     A router SHOULD NOT forward, except over a loopback interface, any
>     packet that has a destination address on network 127.  A router
>     MAY have a switch that allows the network manager to disable these
>     checks.  If such a switch is provided, it MUST default to
>     performing the checks.

In addition to the comments above about IPv6 address formatting, the
improper use of "loopback" terminology as it applies to IPv6, and
concerns about using localhost: it's worth noting that this text in
RFC 1812 refers to IPv4 routers -- RFC 8504 has no equivalent language,
and so the use of ::ffff:127.0.0.0/104 implies no special router handling.
::1 *probably* does, at least as a practical matter.