Silviu,
A
router can receive an RA on the router's upstream and use this RA to
autoconfigure the ipv6 address on interface(s) of the router. Such a router
interface configuration is no different from how a host interface
statelessly autoconfigures as per ND RFC 4861 and 4862.
I agree and I also thought that this should be possible.
However, ND RFC's do not
mandate what does a router implementation do for sending RA, configuring network
prefixes in the router downstream direction - these are conceptual variables
that a router vendor is left to do what they want to do.
Noticed that too :)
As to answering your question which was:
"Why wouldn't a router be authorized
to send Router Sollicitation messages?"
My question was related to sending Router Sollicitations on the upstream interface.
here is my reply.
As far as the interface on the router
has no RA configured, and the interface is configuring an IPv6 address using
stateless autoconfiguration or even manual configuration, this interface is OK
to send an RS in the router downstream.
As I understand, a router could configure its "downstream" interfaces by RAs received from other routers in the "downstream". Is it correct?
This way, the notion of up/downstream would loose its sense.
However, soon
as any RA configuration for router downstream is configured on the network
interface, then ND prohibits a router to send any RS.
But if the downstream interface would have already been configured as discussed previously, where is the interest of having a prefix delegated for this downstream interface to advertise?
Furthermore, I totally agree with Remi on his reply to this question of
yours:
"The same question for
autoconfiguring the prefix it advertises on its
subnets."
You cannot mix router upstream and downstream operations in random
fashion. IPv6 stateless autoconfiguration does not support prefix and router
configuration of an upstream router. One should be careful discussing
router downstream vs. router upstream directions for address configuration,
routing configuration, and IPv6 ND RA configuration.
Sorry for my English, probably not the best these days.
I try not to mess things up. The reason I wrote here is that I have seen a solution (
ICMPv6 Based Prefix Delegation, expired) for delegating prefixes with (modified) NDP. In one of the reactions at this draft, it was mentioned that routers do not send RS messages but it wasn't mentioned why wouldn't they.
I think that the approach is interesting. I don't know if you already have an opinion on it.
Thanks.
--
Silviu
Hello,
I have been trying to figure out a response for the
following questions, but I have only suppositions and I haven't found (yet) a
document that accurately talks about. So I am asking here.
Why wouldn't a
router be authorized to send Router Sollicitation messages?
Moreover, why
couldn't a router autoconfigure its egress interface based on Router
Advertisements received on this interface? The same question for autoconfiguring
the prefix it advertises on its subnets.
The only answer that comes in my
mind is because an attack over these messages could render not only a host
unreachable, but maybe a whole subnet. But apart this, is there really any other
reason for not allowing this?
Thank you in advance for the
answers.
Best regards,
--
Silviu
