Subject: Suggestion for Subnet-Router anycast address section of draft-ietf-6man-rfc4291bis

From: Erik Auerswald <[email-masked]>
Date: Thu, 20 Jul 2017 18:45:57 +0200

Hi,

I have recently tried to implement 127-bit prefixes on inter-router
point-to-point links [RFC6164]. The vendor gear used supposedly supported
the RFC, but it created the Subnet-Router anycast address for that link
in contradiction to RFC 6164. As a result one router answered to both
addresses, that is the odd (LSB==1) address configured on the interface
as well as the even (LSB==0) Subnet-Router anycast address for the link.

Reading just RFC 4291 section 2.6.1 respectively the current version of
draft-ietf-6man-rfc4291bis section 2.5.1, it is not clear from the section
"Required Anycast Address" that the Subnet-Router anycast address MUST
be disabled for /127 prefixes as per RFC 6164, section 6.

Thus I suggest the following text to be added to draft-ietf-6man-rfc4291bis
section 2.5.1. to the second-to-last paragraph:

    , except for inter-router point-to-point links using 127-bit
    prefixes [RFC6164]

The paragraph would be changed to the following text:

    Packets sent to the Subnet-Router anycast address will be delivered
    to one router on the subnet. All routers are required to support the
    Subnet-Router anycast addresses for the subnets to which they have
    interfaces, except for inter-router point-to-point links using 
    127-bit prefixes [RFC6164].

It would be great if you could add some text to section 2.5.1. of
draft-ietf-6man-rfc4291bis to clarify this issue. Feel free to use the
text suggested by me, or any other wording you may prefer. That change
might make it simpler for implementers to consider the corner case of
127-bit prefixes.

Thanks,
Erik
-- 
Dipl.-Inform. Erik Auerswald         http://www.fg-networking.de/
[email-masked] T:+49-631-4149988-0 M:+49-176-64228513

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