Where you configure a mask with an address is an accident of the UI.
Where you use the mask is based on the protocol design. The prefix
length is not used in any way with an address assigned to an
interface. The only reason a mask is specified with an address in
IPv4 is to convey on-link prefix information. That information is
provided through RAs in IPv6. Therefore there is no need to provide
a prefix length with an assigned IPv6 address, whether that address
is assigned through SLAAC, DHCPv6, manual assignment or divine
intervention.
- Ralph
On Aug 15, 2007, at Aug 15, 2007,9:13 AM, Iljitsch van Beijnum wrote:
On 15-aug-2007, at 12:15, Mark Smith wrote:
I disagree. For better or for worse, the notion of a subnet mask
going along with an interface address is deeply ingrained in the way
IP is implemented. Separating the two for no apparent reason is a
bad
idea.
I think you need to modify the following sentence as such:
"For better or for worse, the notion of a subnet mask
going along with an interface address is deeply ingrained in the way
**IPv4** is implemented."
No, I was very careful about what I said. The only place that I can
think of where you don't configure a mask along with an address is
in the case of HSRP. EVERYWHERE else that I know of you need to
specify it now that we have CIDR and obviously it was implied
before we had CIDR. Yes, in IPv6, too.
We can talk long and hard about the pros and cons of this
architecturally, but the simple truth is that changing this doesn't
appear to buy as anything tangible and it will require huge amounts
of work in implementations and then generate huge amounts of
confusion in operations so PLEASE let's not go down this road.
And if you have to look back before RFC 791 to provide
counterexamples that really doesn't disprove "ingrained" in my
opinion...
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