Using an *external* DHCPv6 server for prefix-delegation in conjunction with PPPoE

[Ole Troan]

Per,

> After playing a bit more, I can answer my questions my self.
> 
>>> If you create a loopback interface with an PD address and use that as
>>> unnumbered addresson the WAN interface, does that work?
>> 
>> Yes, at least on a 1841 running 15.1(3)T [0].
> 
> It's even better: You can directly assign a PD address on the WAN interface:
> 
> interface FastEthernet0/1.1600
> encapsulation dot1Q 1600
> ipv6 address PREFIX ::/64 eui-64
> ipv6 enable
> ipv6 nd autoconfig default-route
> ipv6 dhcp client pd PREFIX rapid-commit
> end

it would be cleaner and more in the spirit of RFC3633 and "http://tools.ietf.org/html/draft-ietf-v6ops-ipv6-cpe-router-09" if you assigned the address to a loopback interface.

e.g:
interface FastEthernet0/1.1600
 # CPE interface with "Basic CPE behaviour"
 encapsulation dot1Q 1600
 ipv6 address autoconfig default   ! will "fail" in your case, but does router discovery (sends RS)
 ipv6 address dhcp                 ! fails in your case
 ipv6 dhcp client pd PREFIX rapid-commit
 ipv6 nd suppress-ra               ! don't send RA messages from the CPE on the WAN interface
!
interface Loopback0
 ipv6 address PREFIX 0:0:0:FFFF::1/64  ! use the last prefix for the internal loopback
!
interface FastEthernet0/0
 ipv6 address PREFIX ::/64 eui-64  ! use the first prefix for the customer LAN
!

in this example the WAN interface tries both SLAAC and DHCP to acquire an address. this works fine in your case with link-local only also. just make sure you send an empty RA on the WAN link.

cheers,
Ole