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

[Erik Auerswald]

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