[dns-operations] 答复: L-Root IPv6 Address renumbering

Terry Manderson terry.manderson at icann.org
Tue Mar 15 00:51:22 UTC 2016

On 15/03/2016, 1:39 AM, "Robert Edmonds" <edmonds at mycre.ws> wrote:

>Hi, Terry:
>I don't think anyone asked this in the thread, but can you talk about
>what the underlying reason is for the re-numbering? Given all the
>operational burdens mentioned above, it sounds like something that
>wouldn't be considered lightly.

Hi Rob,

Great question.

It wasn't considered lightly, there has been considerable time thinking
through this as to what real benefit we (and by "we" I then include all of
the consumers of L-Root) get from it.

The rationale behind the renumbering is that the current IPv6 prefix,
2001:500:3::/48, comes as a direct minimum assignment. We were unable to
expand that allocation to a /47. What we (and I'm sure others) have
noticed is that ISPs and transit providers filter on allocation
boundaries, and constrain RIBs to the minimum allocation size. So our
reach for doing traffic engineering with a /48 is quite limited, noting
the first step in the BGP route selection state machine is generally the
prefix length.

The new address (2001:500:9f::42) sits in the prefix 2001:500:9E::/47,
which then allows us to get 'reach' of the more specific 2001:500:9F::/48
for traffic engineering purposes when we need it across the L-Root
constellation on IPv6.

We do this already on IPv4 using and

Hope this helps.

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