IPv6 RA vs DHCPv6 - The chosen one?

TJ trejrco at gmail.com
Wed Dec 28 15:28:31 UTC 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

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

>                                                 Masataka Ohta


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