Mark Smith a écrit :
On Wed, 18 Feb 2009 21:03:54 +0100 Alexandru Petrescu
<alexandru.petre...@gmail.com> wrote:
Dunn, Jeffrey H. a écrit :
Alex,
While I believe that Suresh is correct in the case of RFC 2464, I
am very interested in the Ethernet implementation that supports
non-64 bit IID. Do you have a reference for this implementation?
Further, are you interested in supporting non-64 bit network
prefixes? If so, let me know offline and we can discuss.
Hi Jeff, this (non-rfc2464 IIDs) is possible for other reasons, but
hasn't been implemented. I'm happy interest is expressed.
In the previous mail I meant to say typical 64bit Ethernet IIDs but
shorter prefix (shorter than 64bit, for example 56bit). This
implementation is what I meant I know exists.
Why is this useful? BEcause it is easier to send RAs with a prefix
length that reflects the prefix length really assigned to that
router.
Isn't a /64 big enough for all conceivable and practical subnets ?
Well yes. I think /64 is big enough, maybe more than necessary.
But if I'm allocated a /48 and do a few subnetting I arrive to around
/56 or /60 to my edge networks. Thus I don't understand why forcing
them to be /64.
Some people want to make that longer because they consider it to be
way too much!
Well yes, I have even crazier ideas - non-contiguous prefixes (reuse the
wasted fffe space in the middle of the IID), but here I'm not
complaining about that. It'll never fly at IETF anyways.
Actually I'm very surprised to learn people seem to agree all
Ethernet links should have precisely 64bit prefixes in the RAs.
It's all links, not just Ethernet, because it's simpler to work with.
If every subnet is a constant /64, then you never need to specify
it, and nobody can ever make configuration errors.
>
Variable length node addresses in IPv4 make sense because IPv4's
address space is small and tight. With 128 bit IPv6 addresses, there
isn't that issue, so operational simplicity becomes more important.
Well operational simplicity may be apparent, sometimes not :-)
A typical dialogue goes like this:
"how much IPv6 space do you need for your network?"
"what's IPv6?"
"ok, here you go a RA /64 is large enough for you, and Ethernet SLAAC
can't do otherwise anyways"
"thanks!"
ten days later
"but how could I ever subnet that?"
Were it to say SLAAC Ethernet could be a /56 then people could further
subnet between /56 and /64.
This is just one effect, and there are more like that.
Alex
--------------------------------------------------------------------
IETF IPv6 working group mailing list
ipv6@ietf.org
Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
--------------------------------------------------------------------
