Re: Universal/Local Bit

Hi Ravi,

  Great ...Thanks for clarifying with reference.

Regards
Anantha Subramanian Natarajan

On Tue, Jun 23, 2009 at 9:02 AM, Ravi Singh <way2ccie_at_googlemail.com> wrote:

> Hi Anantha,
>
> That is a nice question IMO, Below is an excerpt from the RFC 4291 for IPv6
> addressing architecture
>
> "*The motivation for inverting the "u" bit when forming an interface*
> * identifier is to make it easy for system administrators to hand*
> * configure non-global identifiers when hardware tokens are not*
> * available. This is expected to be the case for serial links and*
> * tunnel end-points, for example. The alternative would have been for*
> * these to be of the form 0200:0:0:1, 0200:0:0:2, etc., instead of the*
> * much simpler 0:0:0:1, 0:0:0:2, etc.*
> * *
> * IPv6 nodes are not required to validate that interface identifiers*
> * created with modified EUI-64 tokens with the "u" bit set to universal*
> * are unique.*
> * *
> * The use of the universal/local bit in the Modified EUI-64 format*
> * identifier is to allow development of future technology that can take*
> * advantage of interface identifiers with universal scope.* "
>
> As I have understood it, there is not much significance of the U/L bit as
> of now and it's just a way of providing network administrators a method of
> manually deriving endpoint IP addresses .
>
> HTH,
> Ravi
>
> On Tue, Jun 23, 2009 at 1:48 PM, Scott Morris<swm_at_emanon.com> wrote:
> > heheheheh.... There is no need. :)
> >
> > It's an academic one! If you modify your MAC you're supposed to change
> > that. IMHO, if you can't figure out there was something modified in
> > order to go from 48 bits to 64 bits, you need therapy. But it's part
> > of the spec. Go figure.
> >
> >
> >
> >
> > *Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider) #4713,
> >
> > JNCIE-M #153, JNCIS-ER, CISSP, et al.
> >
> > CCSI #21903, JNCI-M, JNCI-ER
> >
> > swm_at_emanon.com
> >
> >
> > Knowledge is power.
> >
> > Power corrupts.
> >
> > Study hard and be Eeeeviiiil......
> >
> >
> >
> > Anantha Subramanian Natarajan wrote:
> >> Hi All,
> >>
> >> I am trying to understand the need for inverting the U/L bit(7th MSB
> bit)
> >> to get the modfied EUI-64 address for IPV6.My understanding is,FFFE is
> >> inserted in middle to increase the size from 48 bit mac address to 64 so
> >> that we could be able to accomdate ipv6 /64 host spacing and couldn't
> >> understand why we invert U/L bit.Thanks for the assistance.
> >>
> >> Regards
> >> Anantha Subramanian Natarajan
> >>
> >>
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Received on Tue Jun 23 2009 - 09:21:13 ART