IPv6 RA vs DHCPv6 - The chosen one?

TJ trejrco at gmail.com
Wed Dec 28 09:28:31 CST 2011


2011/12/28 Masataka Ohta <mohta at necom830.hpcl.titech.ac.jp>

> Valdis.Kletnieks at vt.edu wrote:
>


> <SNIP>
>
> >> In this case, the following statement in RFC1883:
> >>>    If the minimum time for rebooting the node is known (often more than
> >>>    6 seconds),
> >> is the wrong assumption which made RA annoying.
> >
> > Oddly enough, a lot of us are running on networks where assuming this
> about end
> > user gear is perfectly reasonable.
>
> That is because, as I wrote already in the previous mail,
>
> >       Network configuration was mostly stationary
>
> For example, IPv6 might work well, if most of your end users
> are not moving rapidly between small mobile cells.
>
> However, assuming you change the cells every 100m in average
> and you are moving at 100km/h, you must change the cells every
> 3.6 seconds in average, which means you must be able to change
> the cells frequently, which means each cell change take a lot
> less than 3.6 seconds.
>

To me, that sounds like an argument in favor of SLAAC.  SLAAC is noticeably
faster in my experience than DHCP (v4 or v6).  Also, RAs can be sent in the
ms range - for environments that expect that type of attachment-point-churn
...

Also:
Isn't 100m an arbitrarily tight range for a cel tower?
And for cellular, isn't the real churn happening more at the Layer2 side
... no L3/IPv6/IPv4 interaction?



> > We haven't seen many consumer-grade
> > Windows, Macs, or Linux boxes that are able to reboot in much under 6
> seconds.
>
> IPv6 is wrongly architected, not because it assumes nodes are
> able to reboot in much under 6 seconds, but because it assumes
> new configurations necessary only at boot time.
>

Boot time, or anytime a change in network attachment point is detected ...
is that not sufficient?


> Yes, I know you can do it with careful tuning and throwing SSDs and other
> > hardware at it - doesn't mean it's common.
>
> Obviously, the IPv6 committee and you are assuming computers
> of immobile main frame computers or, at least, immobile
> workstations.
>
> However, in the real world, commonly available mobile phones
> are IP capable computers which wake up from dormant state
> within a second and needs handover often within a second.
>

Again, if we are arguing about simple speed of address attainment - SLAAC
wins.



>                                                 Masataka Ohta
>


/TJ


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