ipv6, stateful config and non-default prefixlen
Eugene M. Zheganin
eugene at zhegan.in
Sat Mar 19 08:34:43 UTC 2011
On 18.03.2011 23:56, sthaug at nethelp.no wrote:
> Are you using IA_PD or IA_NA on your DHCPv6 server?
Since I didn't configure anything on a DHCPv6 server about PD, I assume
I'm using NA.
> rtadvd can give you the default router.
> DHCPv6 IA_NA gives you a single /128 address and no netmask.
> DHCPv6 IA_PD gives you a prefix (with the netmask of your choice), but
> I don't know whether FreeBSD can (easily) use this.
I don't see a relation between these 2 things. Prefix delegation is used
to assign prefixes to client _routers_, without knowing about the
topology. I'm configuring a _workstation_. I don't need a prefix to
assign addresses to other computers, I don't have a network behind this
workstation, I need to know about my prefix, and I have that information
in ndp cache, although it is somehow useless.
> As mentioned, DHCPv6 IA_PD gives you a prefix. And ISC dhclient can ask
> for it, see the the -P option.
"The Prefix Delegation options provide a mechanism for
automateddelegation of IPv6 prefixes using the Dynamic Host
Configuration Protocol (DHCP). This mechanism is intended for delegating
a long-lived prefix from a delegating router to a requesting router,
acrossan administrative boundary, where the delegating router does not
require knowledge about the topology of the links in the network to
which the prefixes will be assigned." And that's from RFC.
> If you use DHCPv6 IA_NA, you receive a single /128 address (it is /128
> by definition, the DHCP answer doesn't include a netmask).
That seems to be a mistake. Look what explanation I found in the ietf
"Interface addresses are completely SEPARATE from routing
information.Please do NOT confuse the two. This has been a source of
confusion formany IPv6 implementors who know IPv4.The configuration of
addresses for an interface MUST NOT be tied to the configuration of
prefix information for routing. Just because a prefix is on a link, does
not mean the interface necessarily has an address for that prefix (it
may have none, 1, or many). Just because an interface has an address,
does not mean that the system has any prefix information for a prefix
that "contains" that address. Prefix information and addresses assigned
to interfaces are completely separate."
So it's just an address. Not a /128, just an address.
> You should *not* expect to reach other computers on the link through such a /128
So, in other words, DHCPv6 is useless. No, I don't think so. I have a
bunch of windows on the same link, working with the same DHCPv6 server,
and doing just fine. And that's sad, because I used to think that
FreeBSD is always a queen of the network, far ahead of the
non-truly-networked OS bunch. I'm still hoping that this /64 prefix
issue is related to my low knowledge.
P.S. And I know that autoconfiguration won't work on a link with /120.
And of course, THAT is the reason why I'm using the DHCPv6.
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