v6 & DSL / Cable modems

TJ trejrco at gmail.com
Sun Feb 8 22:24:08 UTC 2009

>> > I suppose you can individually configure every host to get itself
>> > temporary addresses from RA announcements.  This isn't usually a
>> > good default configuration, but OS implementation already seems to
>> > be inconsistent on the default configuration here.  So we're back to
>> > the IPv4 dark ages where you have to walk around to all the devices
>> > to effect changes in policy (beyond prefix field contents).
>> I'm not sure, but you seem to be implying that you need to configure
>> hosts to tell them to use RA or DHCPv6 to get addresses. My apologies
>> if this is not your intention.
>> RA messages are always going to be sent by routers and received by
>> hosts, even if DHCPv6 is being used for address assignment.
>This does not seem to be generally true:
>- For the routers I am most familiar with (Juniper M/MX), you need to
>explicitly turn on router advertisement to make the router perform this.
>I.e. it is perfectly possible to have an interface with an IPv6 address
>which does *not* send RAs.

Yes, vendors differ ... for Ciso/IOS - broadcast capable, multi-access
interfaces (a la Ethernet) will automatically send RAs ones a /64 IPv6
address is configured.  Or once you explicitly tell it to advertise one.

>- For the operating system I am most familiar with (FreeBSD), RAs are
>*not* accepted by default if the interface in question is configured with a
>static IPv6 address.

I don't believe that is the general behavior, and specifically - for Win* a
static being configured does not prevent autoconfiguration.
And this is the correct behavior - to allow for cases where multiple
prefixes are correct/expected, and only one is static.

>Both of these choices seem perfectly reasonable to me.

I slightly disagree on the latter; autoconfiguration in the presence of RAs
(including a (or several) prefix options) should be the default.

((... and now begins (continues, really) the pseudo-religious debate between
the autoconfiguration people and the DHCPv6 people ...))

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