Misconceptions, was: IPv6 RA vs DHCPv6 - The chosen one?

Steven Bellovin smb at cs.columbia.edu
Thu Dec 29 23:37:20 UTC 2011

On Dec 29, 2011, at 5:30 16PM, Masataka Ohta wrote:

> Valdis.Kletnieks at vt.edu wrote:
>>> IGP snooping is not necessary if the host have only one next
>>> hop router.
>> You don't need an IGP either at that point, no matter what some paper from
>> years ago tries to assert. :)
> IGP is the way for routers advertise their existence,
> though, in this simplest case, an incomplete proxy of
> relying on a default router works correctly.
> Beyond that, if there are multiple routers, having a default
> router and relying on the default router for forwarding to
> other routers and/or supplying ICMP redirects stops working
> when the default router, the single point of failure, goes
> down, which is the incompleteness and/or incorrectness
> predicted by the paper of the end to end argument.
> Considering that the reason to have multiple routers
> should be for redundancy, there is no point to use
> one of them as the default router.

VRRP?  The Router Discovery Protocol (RFC 1256).  But given
how much more reliable routers are today than in 1984, I'm
not convinced it's that necessary these days.
> Developing more complicated IGP proxy makes the
> incompleteness and the incorrectness not disappear but
> more complicated.
> 					Masataka Ohta
> PS
> Note that the paper was written in 1984, where as RFC791
> was written in 1981.
There was a lot less understanding of the difference between hosts
and routers in 1984 than there is today -- if nothing else, note
how 4.2BSD and 4.3BSD considered all multihomed machines to be

		--Steve Bellovin, https://www.cs.columbia.edu/~smb

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